Light‐up the white light emission in microscale with a superior deep‐blue AIE fiber as wave‐guiding source

The development of high‐performance organic blue light‐emitting emitters is in urgent to act as an excitation source to contribute the white light generation. On the other hand, the investigation on optical waveguides have been received increasing attentions because they can manipulate the light propagation accurately in the microscale to boost the optoelectronic and energy conversion applications. In this work, we facilely prepared a deep‐blue aggregation‐induced emission (AIE) dye, namely TPP‐4OMe, which shows high luminescent efficiency, narrow emission band and good stability in the aggregate state. TPP‐4OMe can be fabricated as deep‐blue AIE microfibers readily with definite morphology and composition. Based on the AIE microfibers, the active waveguide to transmit deep‐blue emission signals can be achieved with a very low optical loss coefficient (α) of 6.7 × 10−3 dB μm−1. Meanwhile, the full‐visible broadband low‐loss passive waveguide can be well performed with these AIE microfibers, which has never been observed in the pure organic crystals. More interestingly, the excellent properties of AIE microfibers enable them to act as a wave‐guiding excitation source, resulting in a distinct and pure white light emission. The present work not only provides excellent blue light‐emitting materials but also bridges the waveguide to realize the efficient white light emission to accelerate the practical applications.

14] Such technology holds great merits for increasing the quality of human life around the world, and therefore was honored with the Nobel Prize in physics for 2014.17][18][19][20][21] However, it is still challenging to obtain an ideal organic blue emitter.[24] Meanwhile, the generated emission spectra are usually broad, therefore affecting the light purity.Moreover, the stability of organic emitters is expectable to be improved in comparison to the inorganic emitters, which is regarded as an indispensable factor in the practical applications. [25,26]Thus, much effort should be paid to develop the advanced blue light-emitting organic materials with high luminescent efficiency, narrow emission band and good stability in the aggregate state.
Organic optical waveguide is a type of dielectric waveguide, which is found in core material typically possessing a higher refractive index than external media (usually air or other media).[29][30] The refractive index of the core material can be controlled by the molecular species as well as their packing models in the aggregate state.This makes it possible to design desirable waveguide structures to meet the different requirements in practical applications.In 2013, Yao et al. controlled unique self-assembled nanostructures through reasonable molecular design, allowing for the confinement and guidance of photons in specific dimensions. [31]On this basis, optical waveguide supports multiple modes, such as basic mode and higher-order mode.34] Besides, organic materials typically have high nonlinear optical properties, which provides them with potential advantages in nonlinear optical applications.In 2018, Wang et al. designed a stimulated emission controlled photonic transistor on a single organic triblock nanowire, which was further amplified through stimulated emission from the donor and optical feedback in the nanowire microcavity, resulting in significant nonlinear amplification of receptor emission. [35]The property of organic optical waveguide relies on the propagation and limitation of light in the materials, which brings new possibilities for the optical and optoelectronic technologies based on conceivable material design. [36,37][68] This enables TPP-based AIE luminogens very promising to fabricate as high-efficiency blue light-emitting materials for the potential wave-guiding applications.
In this work, based on a building block of TPP, a deep-blue AIE luminogen named TPP-4OMe was obtained through a one-step synthesis.The introduction of methoxy groups onto TPP had a positive effect on its AIE behavior.The resulting intramolecular charge transfer effect induced an obvious emission quenching in the solution while such groups can provide a three-dimensional physical interaction in the aggregate state to restrict the excited-state molecular motions to enhance the emission.The high absolute quantum yield (Φ F ) of 50.9% and very narrow emission with full width at half maximum (FWHM) of 34 nm can be realized in the crystalline powders due to the low configurationally degree of freedom restricted by the strong intermolecular interactions.TPP-4OMe can be facilely fabricated as deep-blue AIE microfibers with their morphology, aggregate-state structure and structural composition well characterized by the scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED) pattern, powder X-ray diffraction (PXRD) and Raman spectroscopy, etc.The AIE microfiber exhibited as a narrow-band deep-blue emission active waveguide with a very low optical loss coefficient (α) of 6.7 × 10 −3 dB μm −1 upon 365-nm laser excitation many thanks to the dense molecular packing, less conformational change and suitable molecular orientation to the light propagation.Moreover, by optical near-field coupling with the visible lasers at different wavelengths, the broadband lowloss passive waveguide can be successfully achieved which provided more opportunities in the practical applications, like conventional telecommunication fibers. [69,70]The photostability of AIE microfibers were proved to be pretty good by comparison to the traditional organic dye.Interestingly, by taking the AIE microfiber as a deep-blue optical waveguding source, the distinct longer-wavelength emissions can be generated through the energy transfer from the AIE microfibers to the coated fluorescent dyes.Especially, the remarkable white light emission with a Commission International de L'Eclairage (CIE) coordinate of (0.33, 0.35) can be generated with the AIE microfiber by engineering the full-color mixing of green and red AIE dyes, therefore providing a powerful tool to extract the substance information and to enhance light-matter interaction in the microscale.

Molecular design and preparation
TPP-4OMe was synthesized by a one-step self-condensation of commercial anisoin in the presence of ammonium acetate, acetic anhydride and acetic acid under reflux (Figure 1A).After the reaction, the precipitates were filtered and recrystallized in the acetic acid to generate the white needlelike crystals in a satisfactory yield.The structure of the molecule was well characterized using 1 H and 13 C NMR and high-resolution mass spectrometry with a satisfactory result (Figures S1-S3).It suggested that TPP-4OMe can be obtained under a facile condition at a low cost, which is suitable for a large-scale production in the practical applications.

Photo-physical investigation
Since TPP-4OMe is a derivative of TPP with four methoxy substituents, how does this structural modification affect its property?To verify it, we studied its UV-Vis absorption and photoluminescence (PL) spectra (Figure 1B).The result indicated that TPP-4OMe possesses an absorption maximum at ∼360 nm in tetrahydrofuran (THF), which is ∼30 nm longer than that of TPP, while the similar bathochromic-shift effect was also found in their emissions.The emission of TPP-4OMe in THF was rather weak.However, after addition of water into the THF with a water ratio at 90%, the nanoaggregates were formed with an average size of ∼230 nm as monitored by dynamic light scattering (Figure S4), which can induce a dramatically enhanced emission at 412 nm (Figure S5).Moreover, the crystalline powder of TPP-4OMe gives a strong deep blue emission at 435 nm with a CIE coordinate of (0.15, 0.03) (Figure 1C), and their absolute PL quantum yield (Φ F ) is recorded as high as 50.9% by an integrating sphere (Table S1).The emissions of TPP-4OMe in the aggregate state is close to our theoretical result that an emission at 427 nm with an oscillator strength (f) = 0.31 was obtained in the molecule based on the investigation of its excited-state property (Figure 1D).Moreover, it is clear that its highest occupied molecular orbital (HOMO) occupied the whole S 1 geometry of molecule while the lowest unoccupied molecular orbital (LUMO) mainly centered at one of its diagonals, suggesting a mixed charge-transfer and local state transitions from the excited state, which may be caused by the introduction of methoxy substituents. [71,72]The transient PL spectra of TPP-4OMe revealed that its excited-state lifetimes (τ) are1.78 ns and 2.15 ns in the nanoaggregates and powder, respectively (Figure S6), which are much higher than that in the solution (0.47 ns).Then, we deduced its radiative decay rate (k r ) and nonradiative decay rate (k nr ) from the formula of k r = Φ F /τ and k nr = (1 − Φ F )/τ, respectively.Interestingly, its k nr had an evident decay from the solution to the nanoaggregates and powder, while the k r increased sharply (Table S1).The reduction in k nr is attributable to the restriction of the excited-state intramolecular motions in the aggregate state.However, due to the intramolecular charge transfer (ICT) effect, the k r have decreased obviously in the polar solvent while such effect can be suppressed by the aggregation.Both factors collectively contribute to an excellent AIE effect of TPP-4OMe.Besides, the FWHM of emission from TPP-4OMe was recognized as 34 nm (Figure 1B,E), which is much narrower than most reported conventional dyes as well as AIE molecules (Tables S2-S3), indicative of an excellent light purity.These features make TPP-4OMe very competent as a solid-state blue emitter.

Morphological and structural characterization
Then, the microfibers of TPP-4OMe were fabricated by a crystal growth in the THF/methanol mixture because such microstructure may meet the promising optical applications.Before the property investigation, their morphological and structural factors were studied.As shown in Figure 2A, the SEM image indicated that the microfiber is one-dimensional rod-like with a diameter and length of ∼10 and 400 μm, respectively.Its surface is very smooth without any optical defects.Under a 365-nm UV light excitation, the whole microfiber can give a deep blue fluorescence thanks to the AIE effect (Figure 2B), while a bright signal could be found at the crystal terminals, indicative of a potential waveguide property.Fortunately, we also obtained a nanocrystal by controlling the growth condition in the same solvent system which is suitable for the further analysis.The TEM image displayed a smooth rod-like structure close to the observation from the SEM with its size much reduced.Moreover, the strong diffraction spots can be observed in the ED pattern, suggestive of a good crystallinity of the nanorod (Figure 2C).The SEM energy dispersive spectroscopy (EDS) mapping images verified a homogeneous distribution of C, O, and N elements in the crystals (Figure 2D-F), suggesting that the molecules are well anchored into the lattice which is in accordance with analysis from the X-ray photoelectron spectroscopy (XPS) (Figure 2G).Then, the Raman spectroscopy was used to characterize the vibrational changes of chemical bonds in the molecular crystals.As shown in Figure 2H, the signal of C-O bonds appeared at ∼1034 cm −1 , which generally exhibited a weak intensity in the Raman spectrum.Besides, the typical signals at ∼1198, ∼1626, and ∼1345 cm −1 were assigned to the C-C bonds, C=C bonds and C=N bonds, respectively.All these suggested an unambiguous chemical bond signals corresponding to the molecular structure.The good crystallinity of TPP-4OMe was further conformed by the PXRD as reflect by its strong diffraction signals (Figure 2I), which agreed well with results from the above analysis.Moreover, its diffraction angles are very close to the results from the pristine powder, suggestive of a definite molecular packing models regardless of the crystallization methods.

Active optical waveguide
With the deep blue AIE microfibers in hand, their optical waveguide properties are further investigated.The optical loss coefficient (α) is a key factor to determine the performance of optical waveguide materials.To achieve such target, the characterization of active waveguide is schematically shown in Figure 3A.A uniform far-field focused UV laser (365 nm) was used to excite the AIE microfiber with a length of ∼100 μm, which was placed on a glass cover slide, at six different local positions along their length.As shown in Figure 3B, the emission intensity at the fixed end (I output ) and excitation point (I input ) were recorded, and by fitting the data points in Figure 3C, a formula of the form I output /I input = Aexp −αd was obtained.Using this formula, the active waveguide propagation loss of AIE microfibers was calculated, where d is the distance between the excitation point and the emission end, and A is the ratio of light intensity emitted from the excitation point to the light intensity propagated along the microfiber.The α value of AIE microfiber was determined to be 6.7 × 10 −3 dB μm −1 .To the best of our knowledge, it is one of the best deep-blue active waveguide organic crystals by combination of a low α, narrow emission band and high luminescent efficiency (Table S4).The low α can be attributed to the reabsorption suppression, high crystallinity and regular shape of AIE microfibers, which can reduce optical loss and light scattering.Moreover, the pump power dependent emission behavior of AIE microfibers was investigated (Figure S7).The results indicated that there was almost no change of emission wavelength with the increasing pump power, while a certain positive correlation relationship between the emission intensity and pump power can be obtained.

Passive optical waveguide
Passive optical waveguides can transmit optical signals within microfibers via total internal reflection without an additional UV excitation source.[75] We measured the passive waveguide loss coefficient through an experimental design as shown in Figure S8.As the absorption wavelength of TPP-4OMe is 365 nm, the AIE microfibers placed on the glass slide were near-field coupled with three lasers above the absorption (473 nm, 532 and 655 nm) at five different local positions along their length.When the input signal was coupled into one middle position of AIE microfiber (Figure 3D-F), the blue, green and red output signals were also observed at both ends except for the coupling point.By changing the distance between the output end and the coupling point, the optical loss during propagation was observed, and it was found that the closer distance between the output end and the coupling point, the stronger the output signal.The laser power at the fixed output end (I WG ) and the coupling point (I EX ) were recorded.The square root of five propagation distances for different wavelengths of laser (S 1/2 ) measured in the experiment was fitted linearly with the logarithm of the laser power at both ends (log10[C]) using an equation of S 1/2 = A*log10[C] + B. The resulting linear relationship is shown in Figure 3G-I, while each propagation distance and laser power showed a good linear correlation (correlation coefficient R 2 > 0.995), indicating that the AIE microfiber can be used for full-visible broadband low-loss passive waveguide.The passive waveguide losses for blue, green and red lasers are 0.166, 0.145, and 0.176 dB μm −1 , respectively.

Stability of AIE fiber
The photostability of AIE microfibers is evaluated because most of the organic dyes are easy to undergo photobleaching under the laser irradiation, resulting in the unsatisfied optical performance, poor imaging quality and serious side effect.The stability experiment was performed on a basic of a continuous irradiation of the AIE microfiber by the 365-nm laser.The results indicated that the AIE microfiber showed a bright emission with its signal decreased slightly as time elapsed.At 60 min, the AIE microfiber still emitted obviously with an emission intensity remaining 82%.Moreover, a comparative study was taken with the commercial fluorescence dye indocyanine green (ICG) as a control (Figure 3J).In a sharp contrast, the emission of ICG aggregates had a dramatic drop in 20 min, and then decayed slowly and almost reached a plateau after 40 min.At 60 min, the signal loss was recorded as 90%, which is five-fold higher than that of AIE microfiber.Figure 3K shows the fluorescence micrographs of the AIE microfibers exposed to 365-nm UV light for 60 min.
The PL spectra recorded during the irradiation have a negligible change in their profiles (Figure 3L).This suggested that the deep blue AIE microfibers possessed an excellent photostability, which is extremely desirable in the practical applications.Besides, by irradiating the AIE microfiber with 405-nm laser of different power, the confocal mapping image of its fluorescence lifetime was also collected.It was revealed that the fluorescence lifetime shows almost no change with the increase of power, further proving that the AIE microfiber had good resistance to optical power (Figure S9).

Aggregate-state information in crystal
Then, the single crystal X-ray diffraction of AIE microfiber was carried out, which may give a deeper insight into the molecular information in the aggregate state to affect its property.The results indicated that the conformation of TPP-4OMe is propeller-like (Figure 4A).The peripheral phenyl rings twisted out the central pyrazine plane with an averaged twisting angle of 39.30 • .This molecular architecture can avoid the strong π-π stacking to form the excimers to quench the fluorescence.On the other hand, the molecules are three-dimensional cross-linked by the other physical interactions.For example, there are multiple intermolecular C-H⋅⋅⋅π hydrogen bonds formed between the hydrogen atoms and phenyl rings or pyrazine rings with distances of 2.738-2.942Å along the a axis (Figure 4B).Moreover, the intermolecular C-H⋅⋅⋅N interactions with a distance of 3.536 Å can be found between hydrogen atoms in the phenyl groups and nitrogen atoms in the adjacent pyrazine rings along the c axis.However, the appended methoxy groups played an important role in the three-dimensional interactions for their multiple sites to facilitate hydrogen bond formation.It is clear that the intermolecular C-H⋅⋅⋅N interactions with distances of 2.814 and 3.009 Å can be generated between the methoxy groups in the closing the molecules, while the strong C-H⋅⋅⋅π interactions with a distance of 2.605 Å can be observed by a synergetic contribution from the methoxy groups and the nearby phenyl rings (Figure 4C).All these factors can guarantee the efficient and narrow emission by prohibiting the excited-state intramolecular motions in the aggregate state.Moreover, the transition dipole (μ) of TPP-4OMe was obtained based on the optimized S 1 geometry in the crystal (Figure 4D).The vector of μ started from the pyrazine plane and pointed diagonally upwards to one of the phenyl groups.The μ adopted an inverse parallel arrangement in the adjacent molecules.It is reported that the light propagation in the molecular crystals is close to the molecular dipoles and a strong reabsorption may occur if the electrical field is parallel to the μ, which can pose a negative effect on the optical waveguides. [74]Considering the low α of our AIE microfiber, the excited-state energy may have a minimum loss in propagation not only because of the favorable orthogonal orientation between the electrical field and μ but also due to the effective intermolecular interactions to restrict the molecular relaxation in the excited state.

Light-up the white emission in microscale
Based on the excellent luminescent efficiency, light purity, stability, and wave-guiding property of the AIE microfibers, they were utilized as a host for a long-range energy deliver to excite the emissions from the other materials by the energy transfer process (Figure 5A).Herein, two AIE dyes of AIE-Green and AIE-Red were employed because they are reported to have strong green and red emissions in the aggregate state, respectively. [75,76]Moreover, their absorption and excitation spectra had a well overlapping with the emission from the AIE microfibers, indicative of a theoretical feasibility for the energy transfer (Figure 5B,C and Figure S10).Then, we doped these dyes into the UV glue, followed by coating them onto the AIE microfiber and curing by the UV light.This processing can keep the AIE microfibers intact while enable a well dispersion of AIE dyes onto the surface.Surprisingly, the AIE microfiber coated by AIE-Green can give a green emission at one side when excited it at another head.The collected spectrum is close to that of AIE-Green by a direct light excitation and the CIE coordinate is calculated as (0.28, 0.59) (Figure 5D).This suggested that the effective energy migration can take place along the AIE microfiber due to the active optical waveguides, while the AIE dye can be pumped to give the emission.Moreover, the AIE microfiber coated with AIE-Red can show a much brighter red emission with a CIE coordinate of (0.61, 0.39) probably due to a higher luminescent efficiency of the red materials (Figure 5E).Thus, combined with energy transfer strategy, the various emissions can be lighted-up through the active wave-guiding effect with our deep-blue AIE mcirofibers.
White light plays an essential role in the illumination and display, especially for micro/nano-scale system.However, the utilization of deep-blue AIE microfibers for realizing the while light in the microscale has never been reported.[79] Since the AIE microfibers can guide a strong blue emission with high purity, their utility in generating white light is highly anticipated.To achieve such target, the above green and red AIE dyes are mixed to ensure that their emissions, together with the deep blue emission, can give a well cover in the visible light region.Our study revealed that, with an optimized ratio of AIE-Green and AIE-red (m/m = 2:1), the distinct white light emission can be observed at the end of the AIE microfiber.The collected spectrum showed a wide profile, which is contributed by the blue emission from the AIE microfiber and the green and red emissions from the AIE dyes through the waveguide excitation and energy transfer.The CIE coordinate of this white light is deduced as (0.33, 0.35) (Figure 5F).Noted that the CIE coordinate of the pure white light is (0.33, 0.33) as defined by International Commission on illumination. [80,81]hus, the obtained result was very close to the ideal value and such outstanding performance make the exploration of substance in microscale very feasible by the aid of the active wave-guiding source from the deep blue AIE microfiber.

CONCLUSION
In this contribution, we prepared a TPP-based AIE luminogen, namely TPP-4OMe through a one-step synthesis.The crystalline powder of TPP-4OMe emitted a deep-blue light at 435 nm with a CIE coordinate of (0.15, 0.03), and possessed a high Φ F of 50.9% and a narrow emission with FWHM of 34 nm due to the low configurationally degree of freedom contributed by the introduction of methoxy substituents to enhance the intermolecular interactions.TPP-4OMe can be fabricated as deep-blue AIE microfibers readily with their morphology, aggregate-state structure and structural composition confirmed by the SEM, TEM, ED pattern, PXRD, and Raman spectroscopy analysis, etc.The AIE microfiber can propagate the deep-blue emission as an active waveguide by the UV light excitation, and its α was deduced as low as 6.7 × 10 −3 dB μm −1 .Alternatively, in the absence of UV light excitation, the passive waveguide can be well performed with the AIE microfibers by near-field coupling the full-visible lights with different wavelengths of 473, 532, and 655 nm, respectively.Based on the excellent emission and active waveguide property, and good photostability of the AIE microfibers, they can be employed as an effective wave-guiding excitation source to light-up the green, red as well as the pure white light emissions in the microscale.The significance of this work is as following: (1) we presented an easy way to obtain organic deep-blue AIE materials with high luminescent efficiency, narrow emission band and good stability in the aggregate state, which is particularly desirable in the practical optoelectronic applications; (2) the AIE luminogen can be fabricated as deep-blue microfibers readily with a definite morphology and composition to exhibit an excellent active optical waveguide by the UV light excitation.Besides, the full-visible broadband low-loss passive waveguide can be realized with the microfibers while the utilization of such pure organic crystals for the passive waveguide has less been reported; (3) thanks to the excellent blue-light emitting and wave-guiding properties of AIE microfibers, it is the first demonstration to employ them as an effective wave-guiding excitation source to light-up the various emissions and even white light emissions by the energy transfer process.As more information can be obtained by light-matter interaction, realizing the white light emission in the microscale is crucial to boost the development of micro light sources, micro displays, and biomedical imaging, etc.We believe, with our deep-blue AIE microfibers, more works will be accelerated to boost the optoelectronic applications in the exploration of the microscopic world.

Materials and instrumentation
All chemicals are purchased from J&K and Energy Chemical and used directly without purification.AIE-Green and AIE-Red are synthesized in our previous literature. [75,76]

Synthesis of TPP-4OMe
Into a 250 mL round-bottom flask was added anisoin (20 g, 73.5 mmol), ammonium acetate (17 g, 220.5 mmol), acetic anhydride (11 mL, 110.3 mmol) in 100 mL acetic acid.The mixture was stirred at reflux for 4 h.After that, the mixture was cooled down to room temperature and the precipitate was filtered and washed with acetic acid.The crude product was recrystallized in hot acetic acid and the white needle-like crystals were obtained in a yield of 23.4%.

Calculation method
The optimization of the excited-state conformation of TPP-4OMe was conducted in Gaussian 09 package [82] at TD-B3LYP/6-31G(d,p).The values of coordinates of the transition dipole moment of S 1 state were output in the final result file.The ONIOM model was used for solid-state optimization in which the central molecule was treated at TD-B3LYP/6-31G(d,p) level and the surrounding molecules were treated by the universal force field.

Passive optical waveguide procedure of AIE fiber
First, the laser is connected to the single-mode fiber to couple the laser into the left end of the AIE microfiber.After stretching and grinding, the beam end angle between the tapered fiber and the laser input is 0.2 • .We know that relatively horizontal coupling end faces can effectively reduce waveguide distortion and improve signal laser transmission efficiency.The coupling end face angle with the AIE microfiber is 5 • .Under the lens of the microscope, it can be seen that the tapered optical fiber transmitting the laser is in good contact with the coupling surface of the AIE microfiber, which is conducive to the realization of evanescent wave near-field coupling; then another tapered optical fiber is coupled to the right end of the AIE optical fiber, where a power meter was connected to the tapered optical fiber.The microscope lens is also used to ensure that the tapered optical fiber is close to the level of the end face of the AIE microfiber, so as to ensure the accuracy of the collected power data.

Coating the AIE dyes on the microfibers
The AIE microfiber was placed on a three-dimensional microscope operating platform, and a certain amount of AIE dye-doped glue was adsorbed through the needle syringe.The glue was then pressed into the microinjection needle using atmospheric pressure, and the microinjection needle was subsequently installed into the digital air pressure microinjection pump (The experimental device was shown in Figure S11A).Then, by moving the microscope observation platform, the microinjection needle was aimed at the top of the AIE microfiber.Figure S11B displays the experimental picture of the AIE microfiber successfully coated with glue.

Waveguide of AIE fiber to light-up the other emissions
By adjusting the micro-stage, the 365-nm incident light was focused on one side of the AIE microfiber, and the generated blue fluorescence generated was waveguided along the microfiber.The blue signal waveguided and excited the AIE-Green coated on the other side of the AIE microfiber.Under the blue light waveguiding of AIE microfiber, the green fluorescence of the AIE-Green at the other side of the microfiber was remotely excited.Using the same method, the red fluorescence from AIE-Red can be excited.After successfully waveguiding excitation of two small molecule fluorescent materials (AIE-Green and AIE-Red), white light emission was generated through three-color recombination of blue, green and red fluorescence.
U R E 1 (A) Synthetic route to TPP-4OMe, and photographs of its powders under room light and UV light.(B) Absorption spectrum of TPP-4OMe in the THF and its photoluminescence (PL) spectrum in the powder.(C) Commission International de L'Eclairage (CIE) color coordinate diagram of TPP-4OMe in the powder.(D) Molecular orbitals based on optimized S 1 geometry of TPP-4OMe.(E) The emission wavelength and FWHM of TPP-4OMe versus other typical aggregation-induced emission (AIE) molecules.
Scanning electron microscopy (SEM) image of aggregation-induced emission (AIE) microfiber.(B) Fluorescence microscopy image of AIE microfiber under 365-nm UV light irradiation.(C) Transmission electron microscopy (TEM) image of AIE nanocrystal, inset: selected area of electron diffraction.(D-F) Element mapping images of C, O, and N elements, respectively.(G) X-ray photoelectron spectroscopy (XPS) characterization of fullspectrum.(H) Raman spectroscopy of AIE microfiber.(I) Powder X-ray diffraction (PXRD) diffractograms of pristine crystalline powder state and AIE fiber.

F I G U R E 3
(A) Graphical illustration of utilizing aggregation-induced emission (AIE) microfiber for active optical waveguide.(B) Fluorescence micrographs obtained by far-field focusing on an identical AIE microfiber at different locations with arrow indicating the direction of propagation.Scale bar: 15 μm.(C) Plot of emission intensity at the end versus the distance between the excited point and the emitted end.(D-F) Optical microscopic images of AIE microfiber near-field coupled with 473, 532, and 655 nm laser at different positions.Scale bar: 50 μm.(G-I) The decay curve of I WG /I EX versus propagation distance.I WG and I EX represent optical power of the output and the input end, respectively.(J) Photostability of AIE microfiber and indocyanine green (ICG) aggregate upon continuous laser irradiation (365 nm, 50 mW/cm 2 ) for 60 min.Time-dependent (K) fluorescence micrographs and (L) fluorescence spectra of the AIE microfibers exposed to 365-nm UV light for 60 min.Scale bar: 50 μm.F I G U R E 4 (A) Molecular conformation and dihedral angles of the peripheral phenyl rings against the central pyrazine ring in the crystal (CCDC 2261868).(B) Intermolecular C-H⋅⋅⋅O and C-H⋅⋅⋅π interactions along a axis.(C) Intermolecular C-H⋅⋅⋅N and C-H⋅⋅⋅π interactions along c axis.(D) Intermolecular C-H⋅⋅⋅O and interactions along b axis and the orientation of μ.
Graphical illustration of deep-blue aggregation-induced emission (AIE) fibers as waveguide source for lighting-up various emissions.(B) Molecular structures of AIE-Green and AIE-Red, and the energy transfer between the AIE molecules.(C) Absorption or emission spectra of TPP-4OMe, AIE-Green, and AIE-Red.(D-F) Emission spectra of waveguiding AIE fibers coated with AIE-Green, AIE-Red, and AIE-Green/AIE-Red-doped UV glue.Inset: Dark-field fluorescent micrograph, while UV light was locally focused on the left side of AIE fibers (marked in dash line) and emission spectra were collected on the right side.The concentration of AIE-Green or AIE-red ≈ 0.5 mg/mL.