SEARCH

SEARCH BY CITATION

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information

In this work, we have quantified for the first time the fluorescence and singlet oxygen quantum yields of a silicon(IV) phthalocyanine bound to the surface of zeolite L nanocrystals. The photophysical properties were correlated with the absorption spectra and the morphology of the nanoparticles, and most importantly, with the fraction of photoactive chromophores. By comparison with the fluorescence and singlet oxygen quantum yields of the free phthalocyaninate in dilute solution (ΦF = 0.50 and Φ = 0.50, respectively), we conclude that for the most efficient nanoparticles nearly 80% of chromophores are active as monomeric units on the surface, as indicated by the corresponding quantum yields (ΦF = 0.40 and Φ = 0.40). We further functionalized and raised the ζ-potential of the best performing nanomaterial to improve its water dispersibility. The functionalization was monitored by thermogravimetric analysis and time-of-flight secondary-ion mass spectrometry, and its influence on the photophysical properties was assessed. The resulting nanomaterials are capable of establishing stable suspensions in water while retaining the ability to form reactive oxygen species upon irradiation with red light. This provides a basis for the rational design of photoactive nanomaterials for photodynamic therapy or water decontamination.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information

In photodynamic therapy, cancer cells or bacteria can be inactivated by irradiation with harmless red or near-infrared light (λ > 650 nm) [1]. This is the region of the electromagnetic spectrum where tissues barely absorb light, leading to large penetration depths. During irradiation, cytotoxic singlet oxygen (1O2) and reactive oxygen species (ROS) are formed by energy transfer from the lowest excited triplet state of a photosensitizer (PS) to molecular oxygen (3O2) [2]. Since the introduction of phthalocyanines (PCs) [3, 4] and porphyrins [5-7] as PS of 1O2, several carriers have been proposed to enhance their solubilities and photophysical properties [8-13]. Indeed, PCs are known for their good 1O2 photoproduction rates, but are usually connected to particularly high hydrophobicities, thus limiting their application in biomedicine. To increase their water solubility, several approaches have been studied [14], for instance, the introduction of amine [15, 16], carboxylate [17] and hydroxyl [18] functions. However, even water-soluble PCs tend to form inactive aggregates due to hydrophobic interactions. This hampers their capacity to photosensitize 1O2, as the stacked molecules release the energy mainly as heat [19]. In the last years, several efforts were conducted to use organic and inorganic transporter systems for PCs, such as liposomes and surfactants to limit aggregation and to control their biodistribution [20, 21]. For instance, the tendency to form aggregates can be restricted by immobilizing the PCs onto a nanostructured surface [22, 23].

Water decontamination is a major challenge that has to be tackled to support human development, providing drinking water at affordable prices. From a huge variety of methods including mechanical filtration, ozone and hypochlorite treatment, chemical [24], electrochemical [25, 26] and photochemical [27-29] strategies have been particularly investigated as efficient and cost-effective alternatives. Photochemical methods, along with the utilization of radiant energy, constitute some of the most attractive ones due to the availability of sunlight in rural and developing areas. An ideal photoactive system is capable of destroying microorganisms upon irradiation, and can be separated from the fluid phase afterward, or eventually be employed in continuous flow processes [30-35]. This is not possible with soluble photosensitizing molecules, and considerable efforts have been made to bind them to solid substrates such as silica [36, 37] or cellulose [38, 39]. However, several organic PSs become less efficient upon adsorption to surfaces, mainly due to π-stacking, which facilitates efficient nonradiative deactivation pathways of photoexcited states, thus diminishing the 1O2 quantum yield (Φ) [40-42].

PCs are photostable, red light-absorbing PSs which can efficiently produce 1O2, provided that they are available as monomeric species [43]. In this sense, Ishii et al. have recently proposed the functionalization of silica with monomeric Si(IV) PCs by condensation of the Si–OH groups of the surfaces with those of the PS [9, 10]. Zeolites, on the other hand, are crystalline aluminosilicates which are readily available and can be easily decanted or filtered out of aqueous solutions, or, alternatively, be bound to surfaces in the form of monolayers [44]. Previous studies have elegantly demonstrated [11, 12] that carefully tailored phthalocyaninates can be anchored to the channel entrances of zeolite L crystals constituting light-harvesting stopcocks. Inspired by these pioneering works, we have recently proposed that PC derivatives can be condensed with the surface of zeolite L nanocrystals [13], which upon loading with fluorophores and functionalization with aminoalkyl silanes are able to bind, to label and to photoinactivate Gram-negative bacteria, such as Escherichia coli and Neisseria gonorrhoeae. However, no quantitative data regarding the photophysical performance of such hybrid architectures has been reported so far, particularly concerning the degree of aggregation of the photosensitizing unit and, consequently, the ΦΔ. In the present work, we address these open questions and present a structure–activity correlation which facilitates the rational design of particulate PSs. Moreover, further functionalization steps are introduced herein to enhance their dispersibility in aqueous environments, and the resulting photosensitizing performance in water is investigated. For this purpose, we carried out a comparative quantitative investigation of the 1O2 photoproduction capability of a Si(IV) phthalocyanine (SiPc) derivative in dilute solution and upon linkage to zeolite L nanoparticles of different shapes and degrees of functionalization. Understanding the correlation between structural features and spectroscopic properties such as fluorescence quantum yield (ΦF) and lifetime (ΦF), absorption spectra and, most importantly, Φ, is crucial for the rational design of particulate photosensitizing materials.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information
General

All chemicals were purchased from commercial suppliers (Aldrich for the dyes, Merck for the solvents, Fluka and Alfa Aesar for synthetic grade chemicals) and used without further purification.

Synthesis of zeolite L nanoparticles

Hydrothermal synthesis of the nano-sized crystals (C) as well as the disk-shaped zeolite L nanoparticles (D) was carried out as previously published by Zabala Ruiz et al. [45].

Functionalization

CS and DS nanoparticles: The functionalization with tetra-t-butyl SiPc (supplied by Sigma-Aldrich) was carried out for nano-sized zeolite L crystals (C) as well as for disk-shaped zeolite L nanoparticles (D) by boiling the dye (20 mg) with the colorless zeolite L material (300 mg) in 50 mL of toluene for 6 h. The large excess of dye is required to achieve reproducible loadings by ensuring the complete coverage of the particles. The resulting blue material (CS and DS) was centrifuged and washed repeatedly by sonicating and boiling in toluene, until no detectable PC absorption was measureable in the supernatant. In this process, the hydroxyl groups of the Si(IV) phthalocyaninate dihydroxide react with the surface of the aluminosilicate, resulting in a covalent linkage between the chromophore and the crystalline carrier [9, 10, 13].

CSA nanoparticles: Afterward, (3-aminopropyl)triethoxysilane (APTES) was linked to the CS particles by adding an equimolar mixture of APTES (500 μL) and triethylamine to a suspension of CS (100 mg) in toluene (25 mL) and sonicating for 1 h, yielding CSA particles. The large excess of APTES is required to achieve reproducible ζ-potentials by ensuring the complete coverage of the particles. Four washing—centrifugation cycles with ethanol removed the remaining reactants.

CSAT nanoparticles: CSA particles were additionally functionalized with tetraethylene glycol (TEG) chains by reacting the amino groups of CSA (100 mg of particles) with TEG p-tosylate (TEG-p-Tos, 182 mg [0.5 mmol], synthesized as described elsewhere [46]) in 25 mL of toluene and refluxing for 2 h. The resulting CSAT particles were washed with ethanol and centrifuged several times.

Structural characterization

Thermogravimetric analysis: The degree of functionalization after every synthetic step was determined by thermogravimetric analysis (TGA) (TGA Q5000 IR, Hi-Res by TA-instruments). The samples were dried in the TGA oven for 4 h at 80°C under flowing helium. Afterward, the organic compounds were oxidized by flowing oxygen with a heating rate of 5°C min−1 up to 1000°C.

TOF-SIMS: All TOF-SIMS measurements were performed on a TOF-SIMS V (IONTOF, Muenster, Germany) using Bi3+ as primary ion with an energy of 25 keV at a current of 0.3 pA. Spectra were acquired for 100 s in bunched mode (focus: 3–5 mm) with a mass resolution of 5000–10 000. The field of view in each experiment was 200 × 200 μm2. Cycling time of the instrument was set to 200 ms, allowing the acquisition of spectra up to a mass-to-charge ratio of 1650. With an ion dose density of 4.83 × 1011 cm−2 all measurements were performed in the static regime.

Dynamic light scattering and ζ-potential: Dynamic light scattering (DLS) and ζ-potential measurements were carried out in bidistilled water with a Malvern Instrument (Zetasizer, Nano ZS). For this purpose, the particles were sonicated for 10 s to establish the suspensions (5 mg of particles in 10 mL of bidestilled water).

Electron microscopy: For SEM images, the samples were deposited on silicon dioxide substrates via drop casting. After evaporation of the solvent, the samples were covered by a 5 nm thick silver layer. The samples were finally investigated using a Zeiss 1540 EsB dual beam focused ion beam/field emission scanning electron microscope, with a working distance of 8 mm and an electronic high tension (EHT) of 3 kV. For TEM analysis, a Zeiss Libra 200FE transmission electron microscope was used. The samples were transferred by drop casting onto the carbon-coated copper grids, followed by drying in air.

Photophysical characterization

Instrumentation for absorption and emission spectroscopy: Electronic absorption spectra were measured using a Varian Cary 5000 double-beam UV–Vis–NIR spectrometer, and are baseline and solvent corrected.

Steady-state fluorescence emission and excitation spectra were recorded using a HORIBA Jobin-Yvon IBH FL-322 Fluorolog 3 spectrometer equipped with excitation and emission double-grating monochromators (1.8 nm mm−1 dispersion, 1800 grooves per mm blazed at 500 nm in the visible spectral range; 3.9 nm mm−1 dispersion, 830 grooves per mm blazed at 1200 nm in the NIR spectral range). The steady-state phosphorescence emission and excitation spectra of 1O2 were recorded using the same spectrometer equipped with an air-cooled Hamamatsu H10330-75 (InP/InGaAs) PMT detector. Emission spectra were corrected for detector sensitivity and emission monochromator blaze angle by the software provided with the equipment; a baseline correction was also performed. Excitation spectra were corrected for source profile (450 W xenon lamp) and emission monochromator blaze angle, by collecting the reference signal with a built-in calibrated photodiode.

Fluorescence time decays were measured on an Edinburgh LifeSpec II spectrometer. An EPL laser diode (635 nm; FHWM <80 ps) with repetition rates between 10 kHz and 1 MHz was used to excite the samples. The excitation sources were mounted directly on the sample chamber at 90° to a double-grating emission monochromator (5.4 nm mm−1 dispersion; 1200 grooves per mm blazed at 500 nm) and collected by a MCP-PMT (Hamamatsu R3809U-50) single-photon counting detector. The photons collected at the detector are correlated by a time-to-amplitude converter (TAC) to the excitation pulse. Signals were collected using a TCC900 plug-in PC card for TCSPC with START and STOP CFDs, variable timing delay, TAC (full range 2.5 ns–50 μs) and Flash ADC, and memory, and data analysis was performed using the commercially available F900 software (Edinburgh Instruments). The quality of the fit was assessed by minimizing the reduced chi-squared function (χ2) and visual inspection of the weighted residuals.

Absorption, fluorescence excitation and emission spectra: All experiments were performed at room temperature. Absorption, fluorescence excitation and emission spectra in air-saturated, spectroscopic grade dichloromethane or bidistilled water, were recorded using a 10 × 10 mm quartz cuvette for fluorescence spectroscopy. The absorption spectra of CS and DS in dichloromethane were straightforwardly measured without significant light-scattering issues, due to the fact that the nanomaterials are readily dispersed in this solvent. For the aqueous samples of CS, CSA and CSAT, the absorption spectra had to be baseline corrected due to scattering of light. Emission spectra were recorded between 650 and 800 nm exciting at 610 nm (absorbances ranged from 0.01 to 0.05). Excitation spectra were acquired between 250 and 730 nm, setting the emission monochromator at 750 nm.

Fluorescence lifetimes: All experiments were performed at room temperature in a 10 × 10 mm pathlength fluorescence quartz cuvette. Solutions in air-saturated, spectroscopic grade dichloromethane or bidistilled water were investigated. Time-resolved measurements were performed in the time-correlated single-photon counting (TCSPC) mode.

Phosphorescence excitation and emission spectra: All experiments were performed at room temperature. Phosphorescence excitation and emission spectra in air-saturated deuterated dichloromethane were recorded using a 10 × 10 mm quartz cuvette for fluorescence spectroscopy. Phosphorescence spectra were recorded between 1100 and 1400 nm exciting at 680 nm (absorbances ranged from 0.1 to 0.2). Excitation spectra were acquired between 300 and 800 nm, setting the detector at 1270 nm.

Fluorescence and singlet oxygen quantum yields: Relative fluorescence quantum yields (ΦF) were determined by comparison with tetra-t-butylphthalocyaninato zinc(II) in toluene as a reference (ΦF = 0.33)[19]. The quantum yields were calculated using Eq. (1), where R and S refer to the reference and sample, respectively, I is the area under the fluorescence spectrum, A is the solution absorbance at the excitation wavelength and (nS/nR)2 is the refractive index correction.

  • display math(1)

Relative singlet oxygen quantum yields (ΦF) were determined by comparison with tetra-t-butylphthalocyaninato zinc(II) in deuterated dichloromethane as a reference (Φ = 0.67)[19]. The infrared phosphorescence spectrum of the photogenerated singlet oxygen was acquired and employed for the quantification of Φ, which was calculated with Eq. (2), where λ1 − λ2 is the irradiation wavelength interval given by the excitation slit width (28 nm, centered at 680 nm), P is the area under the near-infrared phosphorescence spectrum of the photogenerated singlet oxygen, I0(λ) is the incident spectral photon flow, A(λ) is the absorbance and the superscripts S and R stand for sample and reference, respectively.

  • display math(2)

As sample and reference have overlapping spectra and the absorbed wavelength range is narrow, the incident intensity varies smoothly with wavelength and I0 may be approximated by a constant value which may be drawn out of the integrals and canceled.

For CS and DS nanoparticles, the ΦF was measured in dichloromethane (Eq. (1)), and the ΦΔ was quantified in deuterated dichloromethane in the same way by directly measuring the phosphorescence spectrum of 1O2 in the infrared region of the electromagnetic spectrum (Eq. (2)).

For CS, CSA and CSAT particles, ΦF (Eq. (1)) and ΦΔ were measured in water to address their use in aqueous media. Due to the low signals in the infrared, 1O2 photogeneration rates were derived using 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABMADM) as a fluorescent monitor (λex = 380 nm) for photosensitized bleaching rates. Polychromatic irradiation from a projector lamp (Leica ZETT Royal II afs) passing through a cut-off filter at 610 nm was used to carry out the experiments. The ΦΔ for CS, CSA and CSAT was calculated using Eq. (3), where r is the initial slope of the monitor's bleaching over time (rate of 1O2 photogeneration), λ1 − λ2 is the irradiation wavelength interval, I0(λ) the incident spectral photon flow, A(λ)the absorbance and the subscripts R and S are the reference (methylene blue [MB], ΦΔ = 0.52 [47]) and sample (CS, CSA or CSAT), respectively.

  • display math(3)

The incident intensity can be approximated by a constant value, drawn out of the integral and canceled. In Figure S7, the bleaching of the monitor is shown by employing MB, CS, CSA and CSAT nanoparticles.

Results and Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information

Synthesis and structural characterization

Figure 1 shows the structure of tetra-tert-butyl SiPc dihydroxide, which was bound to the surface of the nanoparticles, that are also depicted in Fig. 1. By linking the SiPc onto the surface, aggregation of the chromophores is hindered.

image

Figure 1. Chemical structure of the investigated Si(IV) phthalocyaninate (SiPc); transmission electron micrograph of nano-sized zeolite L crystals (CS); scanning electron micrograph of disk-shaped zeolite L nanoparticles (DS).

Download figure to PowerPoint

In a next step, APTES was reacted with the OH groups on the particles' surface to increase the ζ-potential (vide infra) by the introduction of amino groups able to carry a positive charge by protonation in aqueous environments at pH = 7. In an attempt to further increase the water dispersibility, TEG-p-Tos was reacted with the amino groups introduced in the previous step, which indeed enhanced the stability of the suspensions due to an increased ζ-potential and reduced tendency toward aggregation of the nanocrystals (vide infra).

To confirm the identity of the functional groups attached to the surface, time-of-flight secondary-ion mass spectrometry was employed. It can be observed that DS, CS, CSA and CSAT display characteristic zeolite and phthalocyaninate signals, whereas CSA and CSAT also show APTES-related peaks. On the other hand, only CSAT nanoparticles display a characteristic peak that can be assigned to the TEG-related fragment CH2CH2OCH3+ (compare Figure S3 a–f).

TGA measurements enabled us to quantify the degree of functionalization after every synthetic step (Table 1). A weight loss of −737.97 g mol−1 of SiPc is expected for DS and CS, assuming that only the nonvolatile SiO2 remains after the oxidation process. By taking into account the weight loss due to water evaporation, the molar amount of SiPc per gram of nanomaterial can be calculated. Analogously, the amount of APTES (−59.12 g mol−1 weight loss) as well as TEG (−191.25 g mol−1 weight loss) can be quantified (see Figures S1 and S2). This procedure is possible due to the fact that the same batch of nanoparticles was subsequently functionalized, and a correction by weight loss from previous synthetic steps can be performed. Interestingly, DS particles carry 34% more SiPc than CS, which implies a denser packing of the chromophores and a higher probability of aggregation, as indeed confirmed by the photophysical parameters (vide infra). Remarkably, for every two amino groups, there is only one TEG tail available, although the TEG-p-Tos was used in large excess. This implies a sterical hindrance between the single TEG molecules due to the spatial confinement on the particles' surface.

Table 1. Thermogravimetric analysis of the chemical functionalization
Composition (wt.%)
SampleZeolite LWaterOrganic materialmmol (of added groups)/g (of material)
D94.65.400
DS94.42.23.40.047
C97.42.600
CS97.90.82.50.035
CSA90.22.18.30.998
CSAT81.90.817.80.500

As a consequence of the functionalization with amino groups and TEG-tails, the ζ-potential of the SiPc-coated zeolite L nanoparticles can be tuned from −32.5 mV (CS) to +11.3 mV (CSA) and +32.8 mV (CSAT) (Table 2).

Table 2. Dynamic light scattering and ζ-potential values for disk-shaped and nano-sized zeolites with different functionalization patterns
SampleDiameter (nm)Poly-dispersity indexζ- potential (mV)
D123.00.315−37.4
DS189.80.134−38.1
C130.90.189−59.1
CS112.40.080−32.5
CSA164.70.257+11.3
CSAT133.20.168+32.8

Highly charged particles give stable suspensions in which aggregation is electrostatically hindered (see Table 2). This is reflected by the sizes measured by DLS in water, where higher charged CS and CSAT particles display similar size distributions (112.4 and 133.2 nm in diameter, respectively, see Figure S4) and better monodispersities (polydispersity indices [PDI] of 0.080 and 0.168, respectively) than the lesser charged CSA particles (164.7 nm diameter, PDI of 0.257). Indeed, CSA nanoparticles tend to aggregate and consequently to precipitate out of aqueous suspensions after 30 min. In contrast, suspensions of CS are stable for 2 weeks and suspensions of CSAT for several days.

Photophysics

We investigated SiPc in dilute dichloromethane solutions to understand the behavior of the monomeric species, as well as dichloromethane suspensions of CS and of DS. Furthermore, the photophysical properties of CS, CSA and CSAT were examined in water. In Table 3, the relevant photophysical parameters are listed.

Table 3. Spectroscopic properties of SiPc in solution and at the surface of zeolite L nanoparticles with different functionalizations
Sampleλmax, nm (Soret-band)λmax, nm (Q-band)λmax, nm (emission)ΦF (±0.03)ΦΔ (±0.05)τfluo (aerated), ns (rel. amplitude, %)τfluo (deaerated), ns (rel. amplitude, %)
SiPc (DCM)3556806850.470.525.025.07
DS (DCM)3556806850.270.320.37 (18); 4.99 (82)0.40 (4); 5.06 (96)
CS (DCM)3556806850.390.491.38 (47); 4.61 (53)1.19 (39); 4.82 (61)
CS (aq.)3506866970.330.350.31 (31); 1.27 (42); 2.80 (27)0.30 (27); 1.20 (44); 2.71 (29)
CSA (aq.)3516897010.370.360.24 (26); 1.30 (41); 2.80 (33)0.29 (33); 1.20 (43); 2.66 (24)
CSAT (aq.)3516876980.300.300.21 (21); 1.45 (30); 3.43 (49)0.26 (26); 1.55 (32); 3.42 (42)

In dichloromethane, the nice coincidence of the excitation spectra by monitoring the red PC fluorescence and the near-infrared 1O2 phosphorescence unambiguously proves that the monomeric phthalocyaninate chromophores are exclusively responsible for the fluorescence, as well as for the 1O2 production (see Fig. 2). However, the fluorescence lifetimes clearly display differences between the individual systems, which point to the dissimilar environments sensed by the excited states on the rather irregular surfaces of the two classes of nanoparticles, and is reflected by the resulting multiexponential decays (see Figure S8).

image

Figure 2. Normalized fluorescence (upper row) and phosphorescence (lower row) excitation (dashed line) and emission (solid line) spectra of SiPc (A and D) CS (B and E) and DS (C and F) in dichloromethane.

Download figure to PowerPoint

The absorption spectra display characteristic Soret-bands (355 nm) and Q-bands (680 nm). Moreover, the Q-bands show a progressive broadening into the red that increases with the size of the particles. The smaller CS particles display an absorption spectrum that lies in between those of the SiPc monomer in solution and of DS disks, thus indicating that the higher surface-to-volume ratio of CS nanocrystals hinders the interaction between chromophores more effectively, whereas the DS disks permit a certain degree of lateral intermolecular coupling (see Fig. 3). Due to their shape, the disks possess a much larger relative base area, which probably favors a closer packing of chromophores due to their distinct reactivity, as compared to the coat area [11-13]. This would also explain the higher loading that can be achieved with the disks as compared with the nanocrystals (vide supra). This trend is confirmed by the corresponding quantum yields (vide infra). In aqueous environments, the scattering of light correlates with the stability of the suspensions and the absolute value of the ζ-potential: CS (−32.5 mV) and CSAT (+32.8 mV) are less prone to aggregation and precipitation, as opposed to CSA (+11.3 mV), which also shows the highest degree of light scattering (Figure S6).

image

Figure 3. Normalized absorption spectra of SiPc (solid line), CS (dashed line) and DS (dashed-dotted line) in dichloromethane.

Download figure to PowerPoint

The same tendency is clearly observed in the quantum yields, as the highest and lowest ones are observed for the monomeric SiPc species in homogeneous dichloromethane solution (ΦF = 0.47 ± 0.03, ΦΔ = 0.52 ± 0.05) and in suspensions of the larger DS disks (ΦF = 0.27 ± 0.03, ΦΔ = 0.32 ± 0.05), respectively, whereas the smaller CS nanocrystals (ΦF = 0.39 ± 0.03, ΦΔ = 0.49 ± 0.05) lie in between. Our results regarding the monomeric SiPc species nicely agree with the values reported previously by Oleinick et al. for similar Si(IV) phthalocyaninates in acetonitrile [14]. Assuming that the intermolecular interactions on the surfaces only weakly affect the absorption spectra (roughly saying, two coupled species absorb like a free one), and that the interacting chromophores are inactive (i.e. ΦF = 0, ΦΔ = 0), it is possible to estimate the fraction of actually photosensitizing PC units [43]. We can therefore confidently affirm that on the surfaces of CS and DS nanoparticles 80% and 60% of the chromophores are available as photoactive species, respectively.

The photophysical properties are only marginally affected by the subsequent functionalization steps. Indeed, in aqueous suspensions, the quantum yields are coincident within the experimental uncertainty for CS (ΦF = 0.33 ± 0.03, ΦΔ = 0.35 ± 0.05), CSA (ΦF 0.37 ± 0.03, ΦΔ = 0.36 ± 0.05) and CSAT (ΦF = 0.30 ± 0.03, ΦΔ = 0.30 ± 0.05) implying that on the basis of the fluorescence quantum yields 70%, 78% and 64% of the chromophores are available as active species, respectively (see Table 3, Fig. 4). These values are also in good agreement with those obtained for CS in dichloromethane (vide supra).

image

Figure 4. Normalized fluorescence excitation (dashed line) and emission (solid line) spectra of CS (A) CSA (B) and CSAT (C) in water.

Download figure to PowerPoint

It should be stressed that for DS and CS, the ΦΔ can be measured by direct monitoring of the 1O2 phosphorescence (Eq. (2)) in deuterated dichloromethane, whereas this signal could not be detected, even in deuterated water for CS, CSA and CSAT (the two latter ones cannot be adequately dispersed in dichloromethane). Thus, the photosensitized bleaching rate of a fluorescent monitor was used to quantify indirectly the photoproduction of 1O2, using 9,10-ABMADM in aqueous solution as a fluorescent monitor (λex = 380 nm). Irradiation of stirred, air-saturated solutions of a reference compound (MB, ΦΔ = 0.52 [47]) and either CS, CSA or CSAT in 10 × 10 mm quartz cuvettes lead to a drop of the ABMDMA emission intensity over time. Comparison of the fluorescence bleaching rates (Figure S7) lead to ΦΔ. We cannot exclude that the bleaching of ABMADM is either induced by direct reaction with the PS, with 1O2 or with other derived ROS. Particularly for the CSA and CSAT particles, the functional groups could act as 1O2 traps, leading to a variety of ROS that also bleach the fluorescent monitor. As the PS is surrounded by amino groups (we estimate roughly 100 amino groups attached onto the surface of the particles for every three SiPc molecules, see Table 1), such processes are actually likely to occur. The fact that the phosphorescence of 1O2 was not observable in the aqueous environments, even when deuterated water is employed as a solvent, indicates that the amino groups probably quench the phosphorescence of 1O2, thus preventing its quantitative determination in the near-infrared region of the electromagnetic spectrum (1270 nm). This issue still needs to be addressed more closely, and is presently object of further investigations.

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information

In conclusion, for the first time, we have been able to estimate the fraction of photoactive phthalocyaninates bound to zeolite L nanoparticles, showing that the linkage of the macrocyclic PS to smaller nanocrystals is more efficient to prevent the interaction between chromophores than the attachment to larger disk-shaped nanoparticles. Moreover, these results also prove that the strategy is an efficient way to handle phthalocyaninate PSs, and to retain their photophysical properties by avoiding their aggregation, which otherwise drops their performance. In addition, we were able to correlate the photophysical parameters with the amount of PS attached onto the nanoparticles. The binding of an aminosilane as well as the further functionalization with TEG did not significantly affect the performance of the PS in terms of quantum yields. These findings provide a basis for the rational design of particulate photosensitizing systems.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information

M. G. synthesized and functionalized the nanomaterials, carried out the photophysical and DLS characterization, performed the SEM and TEM characterization, analyzed the resulting data and wrote the manuscript. V. S. carried out the TGA measurements and analyzed the resulting data. B. H. and D. B. carried out the TOF-SIMS measurements and analyzed the resulting data. C. A. S. conceived the experiments, analyzed the data and wrote the manuscript. Financial support from DFG (Deutsche Forschungsgemeinschaft, grant STR1186/1-1) is gratefully acknowledged.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information
  • 1
    Dougherty, T. J., B. W. Henderson, C. J. Gomer, G. Jori, D. Kessel, M. Korbelik, J. Moan and Q. Peng (1998) Photodynamic therapy. J. Natl Cancer Inst. 90, 889905.
  • 2
    Schweitzer, C. and R. Schmidt (2003) Physical mechanisms of generation and deactivation of singlet oxygen. Chem. Rev. 103, 16851757.
  • 3
    Regehly, M., K. Greish, F. Rancan, H. Maeda, F. Böhm and B. Röder (2007) Water-soluble polymer conjugates of ZnPP for photodynamic tumor therapy. Bioconjug. Chem. 18, 494499.
  • 4
    Ishii, K. K., M. Shiine, Y. Shimizu, S. Hoshino, A. Hisaku, K. Sogawa and N. Kobayashi (2008) Control of photobleaching in photodynamic therapy using the photodecarbonylation reaction of ruthenium phthalocyanine complexes via stepwise two-photon excitation. J. Phys. Chem. B 112, 31383143.
  • 5
    Pandey, R. K., K. M. Smith and T. T. Dougherty (1990) Porphyrin dimers as photosensitizers in photodynamic therapy. J. Med. Chem. 33, 20322038.
  • 6
    Schmitt, F., P. Govindaswamy, G. Süss-Fink, W. H. Ang, P. J. Dyson, L. Juillerat-Jeanneret and B. Therrien (2008) Ruthenium porphyrin compounds for photodynamic therapy of cancer. J. Med. Chem. 51, 18111816.
  • 7
    Nishiyama, N., H. R. Stapert, G. Zhang, D. Takasu, D. Jiang, T. Nagano, T. Aida and K. Kataoka (2003) Light-harvesting ionic dendrimer porphyrins as new photosensitizers for photodynamic therapy. Bioconjug. Chem. 14, 5866.
  • 8
    Konan, Y. N., R. Gurny and E. Allemann (2002) State of the art in the delivery of photosensitizers for photodynamic therapy. J. Photochem. Photobiol. B 66, 89106.
  • 9
    Ishii, K., M. Shiine, Y. Kikukawa, N. Kobayashi, T. Shiragami, J. Matsumoto, M. Yasuda, H. Suzuki and H. Yokoi (2007) Silica gel-supported photofunctional silicon phthalocyanine complexes: Photodesorption of molecular oxygen by singlet oxygen generation. Chem. Phys. Lett. 448, 264267.
  • 10
    Ishii, K., Y. Kikukawa, M. Shiine, N. Kobayashi, T. Tsuru, Y. Sakai and A. Sakoda (2008) Synthesis and photophysical properties of silica-gel-supported photofunctional (phthalocyaninato)silicon complexes. Eur. J. Inorg. Chem. 29752981.
  • 11
    Dieu, L.-Q., A. Devaux, I. Lopez-Duarte, M. V. Martinez-Diaz, D. Brühwiler, G. Calzaferri and T. Torres (2008) Novel phthalocyanine-based stopcock for zeolite L. Chem. Commun. 11871189
  • 12
    Lopez-Duarte, I., L.-Q. Dieu, I. Dolamic, M. V. Martinez-Diaz, T. Torres, G. Calzaferri and D. Brühwiler (2011) On the significance of the anchoring group in the design of antenna materials based on phthalocyanine stopcocks and zeolite L. Chem. Eur. J. 17, 18551862.
  • 13
    Strassert, C. A., M. Otter, R. Q. Albuquerque, A. Höne, Y. Vida, B. Maier and L. De Cola (2009) Photoactive hybrid nanomaterial for targeting, labeling, and killing antibiotic-resistant bacteria. Angew. Chem. Int. Ed. 48, 79287931.
  • 14
    He, J., H. E. Larkin, Y. S. Li, D. Rihter, S. I. Zaidi, M. A. Rodgers, H. Mukhtar, M. E. Kenney and N. L. Oleinick (1997) The synthesis, photophysical and photobiological properties and in vitro structure-activity relationships of a set of silicon phthalocyanine PDT photosensitizers. Photochem. Photobiol. 65, 581586.
  • 15
    Jiang, X., S. Yeung, P. Lo, W. Fong and K. P. N. Dennis (2011) Phthalocyanine−polyamine conjugates as highly efficient photosensitizers for photodynamic therapy. J. Med. Chem. 54, 320330.
  • 16
    Li, H., T. J. Jensen, F. R. Fronczek and M. G. Vicente (2008) Syntheses and properties of a series of cationic water-soluble phthalocyanines. J. Med. Chem. 51, 502511.
  • 17
    Liu, W., T. J. Jensen, F. R. Fronczek, R. P. Hammer, K. M. Smith, M. Graca and H. Vicente (2005) Synthesis and cellular studies of nonaggregated water-soluble phthalocyanines. J. Med. Chem. 2005(48), 10331041.
  • 18
    Hu, M., N. Brasseur, S. Z. Yildiz, J. E. van Lier and C. C. Leznoff (1998) Hydroxyphthalocyanines as potential photodynamic agents for cancer therapy. J. Med. Chem. 41, 17891802.
  • 19
    Fernández, D. A., J. Awruch and L. E. Dicelio (1996) Photophysical and aggregation studies of t-butyl-substituted Zn phthalocyanines. Photochem. Photobiol. 63, 784792.
  • 20
    Rodriguez, M. E., F. Morán, A. Bonansea, M. Monetti, D. A. Fernández, C. A. Strassert, V. Rivarola, J. Awruch and L. E. Dicelio (2003) A comparative study of the photophysical and phototoxic properties of octakis(decyloxy)phthalocyaninato zinc(II), incorporated in a hydrophilic polymer, in liposomes and in non-ionic micelles. Photochem. Photobiol. Sci. 2, 988994.
  • 21
    Diz, V. E., G. A. Gauna, C. A. Strassert, J. Awruch and L. E. Dicelio (2010) Photophysical properties of microencapsulated phthalocyanines. J. Porphyr. Phthalocyanines 14, 278283.
  • 22
    Samia, A. C., X. Chem and C. Burda (2003) Semiconductor quantum dots for photodynamic therapy. J. Am. Chem. Soc. 125, 1573615737.
  • 23
    Voskuhl, J., U. Kauscher, M. Gruener, H. Frisch, B. Wibbeling, C. A. Strassert and B. J. Ravoo (2013) A soft supramolecular carrier with enhanced singlet oxygen photosensitizing properties. Soft Matter 9, 24532457.
  • 24
    Yadanaparthi, S. K., D. Graybill and R. von Wandruszka (2009) Adsorbents for the removal of arsenic, cadmium, and lead from contaminated waters. J. Hazard. Mater. 171, 115.
  • 25
    Shi, J., W. Bian and X. Yin (2009) Organic contaminants removal by the technique of pulsed high-voltage discharge in water. J. Hazard. Mater. 171, 924931.
  • 26
    Martínez-Huitle, C. A. and E. Brillas (2008) Electrochemical alternatives for drinking water disinfection. Angew. Chem. Int. Ed. 47, 19982005.
  • 27
    Neyens, E. and J. Baeyens (2003) A review of classic Fenton's peroxidation as an advanced oxidation technique. J. Hazard. Mater. 98, 3350.
  • 28
    Litter, M. I. and N. Quici (2010) Photochemical advanced oxidation processes for water and wastewater treatment. Recent Pat. Eng. 4, 217241.
  • 29
    Legrini, O. E., E. Oliveros and A. M. Braun (1993) Photochemical processes for water treatment. Chem. Rev. 93, 671698.
  • 30
    Meichtry, J. M., H. J. Lin, L. de la Fuente, I. K. Levy, E. A. Gautier, M. A. Blesa and M. I. Litter (2007) Low-cost TiO2 photocatalytic technology for water potabilization in plastic bottles for isolated regions. Photocatalyst fixation. J. Sol. Energ.-TASME 129, 119126.
  • 31
    Marugan, J.. (2010) Supported and immobilized photocatalysts for oxidation of chemical pollutants and inactivation of microorganisms. In Handbook of Photocatalysts (Edited by G. K. Castello), pp. 359384. Nova Science Publishers, Inc., New York.
  • 32
    Zhang, W., L. Zou and L. Wang (2009) Photocatalytic TiO2/adsorbent nanocomposites prepared via wet chemical impregnation for wastewater treatment: A review. Appl. Catal. 371, 19.
  • 33
    Mahendra, S., Q. Li, D. Y. Lyon, L. Brunet and P. J. J. Alvarez (2009) Nanotechnology-enabled water disinfection and microbial control: Merits and limitations. In Nanotechnology Applications for Clean Water (Edited by S. Nora, D. Mamadou, D. Jeremiah, S. Anita, and S. Richard), pp. 157166. William Andrew Publishing, Boston, MA.
  • 34
    Likodimos, V., D. Dionysiou and P. Falaras (2010) Clean water: Water detoxification using innovative photocatalysts. Rev. Environ. Sci. Biotechnol. 9, 8794.
  • 35
    Caslake, L. F., D. J. Connolly, V. Menon, C. M. Duncanson, R. Rojas and J. Tavakoli (2004) Disinfection of contaminated water by using solar irradiation. Appl. Environ. Microbiol. 70, 11451151.
  • 36
    Benabbou, A. K., C. Guillard, S. Pigeot-Rémy, C. Cantau, T. Pigot, P. Lejeune, Z. Derriche and S. Lacombe (2011) Water disinfection using photosensitizers supported on silica. J. Photochem. Photobiol. A 219, 101108.
  • 37
    Amore, S., M. G. Lagorio, L. E. Dicelio and E. San Román (2001) Photophysical properties of supported dyes. Quantum yield calculations in scattering media. Prog. React. Kinet. 26, 159177.
  • 38
    Rodríguez, H. B., A. Iriel and E. S. Román (2006) Energy transfer among dyes on particulate solids. Photochem. Photobiol. 82, 200207.
  • 39
    Zeug, A., J. Zimmermann, B. Roder, M. Gabriela Lagorio and E. San Roman (2002) Microcrystalline cellulose as a carrier for hydrophobic photosensitizers in water. Photochem. Photobiol. Sci. 1, 198203.
  • 40
    Bonnett, R., D. G. Buckley, T. Burrow, A. B. B. Galia, B. Saville and S. P. Songca (1993) Photobactericidal materials based on porphyrins and phthalocyanines. J. Mater. Chem. 3, 323324.
  • 41
    Lacombe, S. and T. Pigot (2010) New materials for sensitized photo-oxygenation. Photochemistry. 38, 307329.
  • 42
    Iriel, A., M. G. Lagorio, L. E. Dicelio and E. San Roman (2002) Photophysics of supported dyes: Phthalocyanine on silanized silica. Phys. Chem. Chem. Phys. 4, 224231.
  • 43
    Strassert, C. A., G. M. Bilmes, J. Awruch and L. E. Dicelio (2008) Comparative photophysical investigation of oxygen and sulfur as covalent linkers on octaalkylamino substituted zinc(II) phthalocyanines. Photochem. Photobiol. Sci. 7, 738747.
  • 44
    Lee, J. S., H. Lim, K. Ha, H. Cheong and K. B. Yoon (2006) Facile monolayer assembly of fluorophore-containing zeolite rods in uniform orientations for anisotropic photoluminescence. Angew. Chem. Int. Ed. 45, 52885292.
  • 45
    Zabala Ruiz, A., D. Brühwiler, T. Ban and G. Calzaferri (2005) Synthesis of zeolite L. Tuning size and morphology. Monatsh. Chem. 136, 7789.
  • 46
    Allampally, N. K., C. A. Strassert and L. De Cola (2012) Luminescent gels by self-assembling platinum complexes. Dalton Trans. 41, 13132.
  • 47
    Wilkinson, F., W. P. Helman and A. B. Ross (1993) Quantum yields for the photosensitized formation of the lowest electronically excited single state of molecular oxygen in solution. J. Phys. Chem. Ref. Data 22, 113262.

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Materials and Methods
  5. Results and Discussion
  6. Conclusion
  7. Acknowledgements
  8. References
  9. Supporting Information
FilenameFormatSizeDescription
php12141-sup-0001-FigS1.jpgimage/jpg1380KFigure S1. TGA weight loss and weight loss per time for DS (red) compared with naked disks (black).
php12141-sup-0002-FigS2.jpgimage/jpg2054KFigure S2. TGA weight loss and weight loss per time for CS (red) compared with naked crystals (black), CSA (blue) and CSAT (green).
php12141-sup-0003-FigS3a.jpgimage/jpg68KFigure S3. TOF-SIMS characterization of C (a), CS (b), CSA (c), CSAT (D), D (e) and DS (f).
php12141-sup-0004-FigS3b.jpgimage/jpg75K 
php12141-sup-0005-FigS3c.jpgimage/jpg77K 
php12141-sup-0006-FigS3d.jpgimage/jpg75K 
php12141-sup-0007-FigS3e.jpgimage/jpg73K 
php12141-sup-0008-FigS3f.jpgimage/jpg73K 
php12141-sup-0009-FigS4.jpgimage/jpg594KFigure S4. Size distribution by DLS for D, DS, C, CS in dichloromethane, and for CS, CSA and CSAT in water at pH = 7.
php12141-sup-0010-FigS5.jpgimage/jpg542KFigure S5. ζ-potential distribution for D, DS, C, CS in dichloromethane, and for CS, CSA and CSAT in water at pH = 7.
php12141-sup-0011-FigS6.jpgimage/jpg884KFigure S6. Uncorrected, normalized absorption spectra of CS (solid line), CSA (dashed line) and CSAT (dashed-dotted line) in water. The scattering increases in the following order: CS < CSAT < CSA.
php12141-sup-0012-FigS7.jpgimage/jpg1499KFigure S7. Emission spectra of ABMADM at different irradiation times with CS (A); MB (D); CSA (B); MB (E); CSAT (C); MB (F). Lower row: Bleaching of ABMADM for samples (triangles) and reference (MB, squares) over time in water: CS (G), CSA (H), CSAT (I).
php12141-sup-0013-FigS8a.jpgimage/jpg87KFigure S8. Fluorescence decay plots for SiPc (a,b), DS (c,d) and CS (e,f) (in aerated/deaerated dichloromethane), and for CS (g,h), CSA (i,j) and CSAT (k,l) (in aerated/deaerated water at pH = 7).
php12141-sup-0014-FigS8b.jpgimage/jpg94K 
php12141-sup-0015-FigS8c.jpgimage/jpg90K 
php12141-sup-0016-FigS8d.jpgimage/jpg94K 
php12141-sup-0017-FigS8e.jpgimage/jpg94K 
php12141-sup-0018-FigS8f.jpgimage/jpg93K 
php12141-sup-0019-FigS8g.jpgimage/jpg97K 
php12141-sup-0020-FigS8h.jpgimage/jpg98K 
php12141-sup-0021-FigS8i.jpgimage/jpg95K 
php12141-sup-0022-FigS8j.jpgimage/jpg97K 
php12141-sup-0023-FigS8k.jpgimage/jpg95K 
php12141-sup-0024-FigS8l.jpgimage/jpg98K 

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.