Continuous Condensed Triplet Accumulation for Irradiance‐Induced Anticounterfeit Afterglow

Abstract Afterglow room‐temperature emission that is independent of autofluorescence after ceasing excitation is a promising technology for state‐of‐the‐art bioimaging and security devices. However, the low brightness of the afterglow emission is a current limitation for using such materials in a variety of applications. Herein, the continuous formation of condensed triplet excitons for brighter afterglow room‐temperature phosphorescence is reported. (S)‐(‐)‐2,2′‐Bis(diphenylphosphino)‐1,1′‐binaphthyl ((S)‐BINAP) incorporated in a crystalline host lattice showed bright green afterglow room‐temperature phosphorescence under strong excitation. The small triplet–triplet absorption cross‐section of (S)‐BINAP in the whole range of visible wavelengths greatly suppressed the deactivation caused by Förster resonance energy transfer from excited states of (S)‐BINAP to the accumulated triplet excitons of (S)‐BINAP under strong continuous excitation. The steady–state concentration of the triplet excitons for (S)‐BINAP reached 2.3 × 10−2 M, producing a bright afterglow. Owing to the brighter afterglow, afterglow detection using individual particles with sizes approaching the diffraction limit in aqueous conditions and irradiance‐dependent anticounterfeiting can be achieved.

For the samples of the demonstration in Figure 1, polycrystalline solid B was spread out by mechanical grinding on a microscope cover glass substrate (Figure 1b (i)).The remaining procedures to complete the anticounterfeit media are explained in the main text.
For the sample of the demonstration in Figure S4, small amounts of crystalline solid B were dispersed on the powder film of solid A on a glass substrate.
For samples to determine the molar absorption coefficient from the ground state by transmittance measurements, solid A or solid B was injected between two microscope cover glass substrates with a gap of 10 µm and set on a hot plate at 240 ℃.The samples are quenched to RT to obtain two amorphous films of solid A and solid B with thicknesses (L) of 10 µm.The two amorphous films were used to determine the optical densities at 360 nm (Abs/L), as shown in Figure 2b.
Regarding the measurement of the emission quantum yield and the emission characteristics shown in Figure 2c and 2d, solid A or solid B were placed on a quartz substrate on a hot plate at 240 ℃.After solid A or solid B melted, another quartz substrate was placed onto the materials to spread out the melted materials between the two quartz substrates.The sandwiched samples were quenched to RT to obtain an amorphous state of solid A or solid B. The amorphous solid A between two quartz substrates was used for the emission quantum yield and emission characteristics of 1 wt% DFAP-doped amorphous β-estradiol in Table 1, Table 2, Figure 2c, and Figure 2d.For the amorphous solid B between two quartz substrates, one quartz substrate was peeled off and then the quartz substrate coated with an amorphous layer of solid B was placed in a DCM vapor atmosphere to crystallize solid B. The crystalline solid B on a quartz substrate was used to obtain the emission quantum yield and emission characteristics of 10 wt% (S)-BINAPdoped crystalline (S)-H8-BINAP in Table 1, Table 2, Figure 2c, and Figure 2d.
Regarding the preparation of films 1 and 2 to obtain the excitation intensity dependence of emission intensity in Figure 3a and 4a, solid A was injected between two microscope cover glass substrates on a hot plate at 240 ℃ and then quenched to RT to obtain film 1 (1 wt% DPAF-doped amorphous β-estradiol layer between two thin glass substrates).For film 2, solid B was injected between two microscope cover glass substrates on a hot plate at 240 ℃ and then quenched to RT to obtain the amorphous layer of 10 wt% (S)-BINAP-doped (S)-H8-BINAP between two thin glass substrates.The sandwiched sample was placed in DCM vapor for a long time to crystallize 10 wt% (S)-BINAP-doped (S)-H8-BINAP to prepare film 2 (10 wt% (S)-BINAP-doped crystalline (S)-H8-BINAP layer between two thin glass substrates).The absorbances at 360 nm caused by photon absorption of films 1 and 2 were 0.106 and 0.122, respectively (Figure S9).
The molecular doping in other molecular crystalline lattices has been reported for fluorescence lasing materials [S3] and persistent phosphorescence materials [S4] .We note that the RTP spectral shape, the RTP yield, and the RTP lifetime of the thin films and single crystals are comparable (Figure S3).

Optical measurements
Absorption spectra of films 1 and 2 were collected using an absorption spectrometer (V-760, Jasco, Ltd., Tokyo, Japan).The absorbances of the amorphous powder and crystalline powder of solid B were measured using an absolute luminescence quantum yield measurement system (G9920-02G, Hamamatsu Photonics, Shizuoka, Japan).The emission yield of the steady-state excitation was determined using the absolute PL measurement system (G9920-02G, Hamamatsu Photonics).The ratio of the fluorescence and afterglow RTP was determined using a photonic multichannel analyzer (C10027-01, Hamamatsu Photonics) as a photodetector and light from an excitation unit of a fluorometer (P-8300, Jasco) to determine the fluorescence (Φr shown in Figure S10a.

Microscopic optical measurements
The relationship between emission intensity and excitation intensity was measured using an inverted optical microscope (IX73, Olympus, Tokyo, Japan) with an oil immersion objective lens (UPlan FLN×100/1.3NA, oil, Olympus).A continuous-wave laser emitting at 360 nm (UV-F-360, CNI) was used as an excitation source to obtain epiemission signals.The excitation beam power was measured using a photodiode power sensor (S130VC, Thorlabs, New Jersey, USA).The excitation area used to determine the excitation power density was determined by observing the emission area from films 1 and 2. A dichroic mirror (FF470-Di01, Semrock, New York, USA) and a long-pass filter (LP02-473RU, Semrock) were used to collect emission signals from films 1 and 2.
Schematic illustration of optical setup is shown in Figure 1d.Steady-state RT emission intensity depending on excitation intensity under the 360 nm excitation was measured.
Persistent RTP intensity depending on excitation intensity was determined from emission intensity within 40 ms after completely ceasing the 360 nm excitation for Figure 3a.By substructing the persistent emission intensity from the steady-state RT emission intensity, the excitation intensity dependence of the fluorescence intensity was determined for

Quantum chemical calculation
Optimized T1 geometry was calculated using density functional theory (DFT) (Gaussian09/B3LYP/6-31G(d)).From the geometry, T-T absorption characteristics were calculated using time-dependent DFT (Gaussian09/B3LYP/6-31G(d)).Single-point calculations were performed using the Amsterdam Density Functional (ADF) 2018 software package for the optimized T1 geometries to determine the T1-S0 energy of the chromophores.For the calculation of kp in DPAF and (S)-BINAP, the spin-orbit matrix elements were treated as a perturbation based on scalar relativistic orbitals using the PBE0 functional and TZP basis sets.The scalar relativistic-time-dependent DFT calculations included 10 singlet + 10 triplet excitations, which were used as the basis for the perturbative expansions in the calculations.

S3. Additional demonstration
Some grains of solid B (crystals) are placed over solid A (amorphous) powder on a glass substrate and set under a fluorescence microscope (Figure S4a).Although afterglow RTP of the film containing solid A and solid B has been measured soon after ceasing excitation at 360 nm and 0.3 mW cm -2 , the location of solids B and A could not be distinguished well (Figure S4b (i)) because they generate comparable intensities of green afterglow emission.However, the afterglow RTP intensity of solid B increases while that of solid A remains small when the excitation intensity at 360 nm increases from 0.3 to 30 mW cm -2 .Therefore, the location of solid B with the size of a few microns could be distinguished (Figure S4b (ii)).When the excitation intensity at 360 nm increases to 300 mW cm -2 , the afterglow RTP intensity of solid B increases further while the RTP intensity of solid A hardly increases.Therefore, more contrast could be observed to distinguish solid B from solid A (Figure S4b (iii)).

S5. Derivation of Equation 1
When the concentration of the ground state (S0) is much larger than that of the lowest triplet excited state (T1) and no exciton annihilation occurs except for triplet-triplet annihilation (TTA) caused by T1 migration, the rate equation for the concentration of T1 based on the conditions ( T 1 ′ ) is expressed as: [S6,S7] where  is the molar absorption coefficient in M -1 cm -1 at 360 nm,  a is Avogadro's constant,  S 0 is the concentration of S0 in M,  t is the triplet generation yield,  p (RT) is the average lifetime of T1 in s, kTT is the rate constant of TTA, and  ex is the excitation irradiance at 360 nm in photons s -1 cm -2 .In Equation S1, the first term represents the generation rate of T1, the second term is the deactivation rate of T1 by TTA, and the third term indicates the deactivation rate of T1 from the T1-S0 transition.Because TTA deactivation was not observed in the data shown in the main manuscript, the second term is ignored to give the following rate equation: The solution of  T 1 ′ in equation S2 is expressed as: S 0 is commonly expressed using the Beer-Lambert law as: where Abs is the absorbance at 360 nm, and L is the thickness of the film in cm.
Combining Equation S3 and S4 results in the following form: Equation S5 is usable in the range of excitation irradiance when the concentration of T1 linearly increases with the elevated excitation irradiance.In real experimental results, the increase of the concentration of T1 becomes saturated under strong excitation.The concentration of T1 when it saturates at elevated excitation irradiance is defined as  T 1 which is expressed using the excitation intensity dependence of the RTP intensity [ p ( ex )] as: [S7,S8]  T 1 =  p ( ex ) where  p ′ ( ex ) is the RTP intensity based on the assumption that the saturation of the RTP intensity with elevated excitation irradiance does not occur.Equation S5 and S6 convert into Equation 1 used in the manuscript:

S6. Estimation of triplet concentration by transient absorption
Because εT-T of DFAP is large, we were able to confirm the concentration of T1 excitons with transient absorption measurements using the optical system of Figure S10a.Red plots in Figure S10b shows the relationship between ΔAbs at 650 nm and the excitation intensity at 360 nm for 1 wt% DFAP-doped amorphous β-estradiol film with a thickness of 2.0 × 10 -4 cm.The red plots in Figure S10b can be represented by the following equation according to the Lambert-Beer law: where L is the thickness of the solid film.When  T 1 at each excitation light intensity is calculated by substituting ΔAbs(650 nm) and the excitation light intensity into Equation S7, the relationship between  T 1 and the excitation intensity at 360 nm is obtained as shown in Figure S10c.Here, the value of εT-T(650 nm) measured in benzene and L = 2.0 × 10 -4 cm were used to determine  T 1 for each excitation intensity at 360 nm.The data for the excitation light intensity dependences of  T 1 are equivalent to the red data in Figure 3b.Therefore, the similarity of the data in Figure S10c and Figure 3b indicates that  T 1 can be reasonably estimated from the pRTP intensity variation and Equation 1.
Transient absorbance is difficult to measure at low excitation intensity.Therefore, determination of  T 1 using pRTP strength and Equation 1 appears to be more accurate.
Furthermore, because of the low value of εT-T of (S)-BINAP,  T 1 could not be determined from ΔAbs, and was instead determined from the pRTP intensity profile and Equation 1. Table S2.Summary of photophysical characteristics of 1.0 wt% DPAF-doped amorphous β-estradiol (film a) and 5.0 wt% DPAF-doped amorphous β-estradiol (film b).

S8. Suppression of T1 accumulation by triplet-triplet annihilation owing to triplet migration at high guest concentration
The reason for this decrease is that additional quenching by triplet-triplet annihilation (TTA) occurs.At low guest concentrations, quenching of FRETS-T or FRETT-T alone provides additional deactivation pathways when the excitation light intensity is high, because T1 of the dye is constrained when the T1 concentration of the dye is sufficiently lower than that of the host (Figure S12a).However, at high concentrations of the guest, T1 migration and quenching by TTA occur (Figure S12b).In fact, in the sample of 10 wt% DFAP-doped amorphous β-estradiol, TTA-based upconversion fluorescence was weakly observed as an afterglow at high excitation light intensity (Figure S13).The two spectra in Figure S13 show the afterglow emission spectral intensities as the excitation light intensity was varied.The spectrum consists of blue afterglow fluorescence and green pRTP.Because the T1 concentration is proportional to the pRTP intensity, the T1 concentration increased to be 1.28 times as high as the excitation intensity from Figure S13a to Figure S13b.At this time the intensity of the blue afterglow fluorescence increased to 1.76, which is approximately the square of 1.28; hence, this blue afterglow fluorescence is likely to be TTA-based upconversion.Therefore, the formation of πinteracting states is not conducive to high T1 concentrations.In 10 wt% (S)-BINAP-doped (S)-H8-BINAP crystalline materials, no TTA-based upconversion fluorescence was observed at high excitation light intensity.(S)-BINAP is well-aligned in the crystal lattice of (S)-H8-BINAP, and interactions between the two molecules are thought to be relatively small owing to the twisted structure.S9] Therefore, conditions that reduce the likelihood of quenching by TTA are also key to achieving a large T1 accumulation.

S9. Mandatory points to be checked to determine 𝑪 𝐓 𝟏 using the excitation intensity dependence of RTP
The following three points (1)-( 3) are must be considered to appropriately estimate  T 1 using the excitation intensity dependence of RTP, which has been partially reported in references S6 and S7.
(1) The absorbance value of the excitation wavelength is small (not near the magnitude of 1 or more, but closer to 0.1 and 0.2).
(2) The absorbance should be measured using films without porous structures and pore sizes that are above the diffraction limit.
(3) Because of (1), estimation using a powder sample is not allowed.
Although bright persistent RT emission is crucial for high-resolution afterglow imaging for bioimaging and anticounterfeit applications, a nanomaterial with a size of less than 1 µm often has small absorbance because of the lower sample thickness.Because the brightness of the nanomaterials is proportional to T1 concentration, the estimation of the upper limit regarding T1 concentration for materials with a small absorbance at the excitation intensity is crucial.For example, we show the common relationship between afterglow RTP intensity and excitation irradiance for two films composed of the same material but with different absorbances, achieved by changing the thickness of the films, where one film has an absorbance of 0.1 at the excitation wavelength and the other film has an absorbance of 3 at the excitation wavelength (Figure S14).For the film with Abs = 0.1, the excitation intensity hardly changes along the depth of the film (Figure S14a).
Because the profile of the T1 concentration is almost the same along the depth direction of the film, the T1 concentration homogeneously increases with excitation irradiance (blue → green → red → black in Figure S14a).Therefore, we can discuss the T1 concentration using the increase of RTP intensity depending on elevated excitation irradiance from the films, as shown in Figure S14b and Figure 3a in the main text.
However, the excitation intensity largely decreases along the depth direction for the film with Abs = 3 (Figure S14c), revealing a distribution of the T1 concentration along the thickness of the sample.Under weak excitation, no saturation of T1 concentration occurs along the depth direction (blue line in Figure S14c).With the increase in excitation power, the T1 concentration (∝ RTP intensity) in the surface region (Figure S14c (i)) becomes saturated with increasing excitation irradiance.However, the T1 concentration (∝ RTP intensity) in the deep region (Figure S14c (ii)) is not saturated compared with that in the surface region.We note the increased RTP intensity in the deep region does not include enough information to determine an upper limit of the T1 concentration.Indeed, such large differences regarding the excitation intensity dependence of RTP intensity were observed for 1 wt% DPAF-doped amorphous β-estradiol film with different absorbances at 360 nm (Figure S15).Compared with 1 wt% DPAF-doped amorphous β-estradiol film with Abs = 0.17 at 360 nm (green plots in Figure S15), 1 wt% DPAF-doped amorphous β-estradiol film with Abs = 2 at 360 nm showed greater RTP intensity under stronger excitation (blue plots in Figure S15).Therefore, we overestimate the T1 concentration when a film with large absorbance at the excitation wavelength is used because the increase of RTP intensity under strong excitation irradiance occurs based on the scheme of Figure S15c.Overestimation of the T1 concentration from the excitation intensity dependence of RTP intensity also occurs when a powder sample is used.This is because absorbance at the excitation wavelength often becomes large (approaching 1) when the excitation beam area is less than the area of the powder sample.
The overestimation of the T1 concentration occurs when the film contains many holes with sizes greater than the diffraction limit.For the porous films, the absorbance value is greatly underestimated because significant irradiated light passes through the absence of material.

S10. Measurement procedure of εT-T
In transient absorption measurements, the Δabsorbance values of the sample and reference (ΔAbs S and ΔAbs R , respectively) are expressed as: where εT-T S and εT-T R are the molar absorption coefficient of sample and reference, respectively, Φt S and Φt R are the triplet generation yield of sample and reference, respectively, Abs S and Abs R are the absorbances at the excitation wavelength of the sample and reference, respectively, α is a constant, and Iex is the excitation irradiance.For the same absorbance at the excitation wavelength, the same Iex and the same optical setup are used for the measurement, and then the following equation is obtained: )  In the experiment used to determine εT-T of DPAF, benzophenone in benzene and DPAF in benzene were used as a reference and sample, respectively.The absorbance of two samples at 355 nm was set to 1.0.ΔAbs S at 640 nm and ΔAbs R at 532 nm under 355 nm excitation were measured (Figure S16).From Figure S16, [ΔAbs S /ΔAbs R ] is obtained.Φt S of DPAF has been reported as 0.61 in benzene.Φt R of benzophenone is known as 1.
The εT-T R of benzophenone is reported as 7.6 × 10 3 M -1 cm -1 at 532 nm in benzene.
To determine εT-T of (S)-BINAP in tetrahydrofuran (THF), Φt R of Bis(2,4difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III) (FIr6) in THF was initially determined.In the experiment, benzophenone in benzene and FIr6 in THF were used as a reference and sample, respectively.The absorbance of two samples at 355 nm was set to 1.0.ΔAbs S at 440 nm and ΔAbs R at 532 nm under 355 nm excitation were measured (Figure S17).Φt R of benzophenone and Φt S of FIr6 in THF are known as 1.The εT-T R of benzophenone is reported as 7.6 × 10 3 M -1 cm -1 at 532 nm in benzene.
Next, the data of εT-T for FIr6 in THF at 440 nm was used to determine εT-T of (S)-BINAP.In the experiment, FIr6 in THF and (S)-BINAP in THF were used as a reference and sample, respectively.The absorbance of two samples at 266 nm was set to 1.0.ΔAbs S at 500 nm and ΔAbs R at 440 nm under 266 nm excitation were measured (Figure S18).
From Figure S18, [ΔAbs S /ΔAbs R ] is obtained.S10] Φt R of FIr6 is known as 1.The εT-T R of FIr6 is 4.5 × 10 3 M -1 cm -1 at 440 nm in THF.Therefore, using Equation S8, εT-T at 500 nm for (S)-BINAP in THF is determined to be 0.83 × 10 3 M -1 cm -1 .The data of εT-T at 500 nm were used for the relationship between εT-T and wavelength (Figure S18c), and Figure S18c was used in the bottom graphs of Figure 4b and 5b.
The  T−T values for DPAF dispersed in amorphous β-estradiol and (S)-BINAP dispersed in crystalline (S)-H8-BINAP were measured using the following procedures.
For the range of Iex showing the linear relationship between ΔAbs() and  ex (), the relationship between ΔAbs() is expressed using the Beer-Lambert law: The equation can be used for wavelengths where the S0 of chromophores does not exist.
From Equation S5 and S11, the following equation is obtained: For films 1 and 2, the relationships between ΔAbs() and Iex were measured (Figure S10b).The linear part of inset in Figure S10b corresponds to a value of  T−T () The  T−T (650) for DPAF doped in amorphous β-estradiol was 3.1 × 10 4 M -1 cm -1 , which was similar to results in benzene.The  T−T () for (S)-BINAP in crystalline (S)-H8-BINAP was difficult to accurately determine because of the noise level, even when strong excitation light was used (Figure S10b).At least, the  T−T for (S)-H8-BINAP in crystalline (S)-H8-BINAP (film 2) was less than that in THF for the whole range of visible wavelengths.Therefore,  T−T for (S)-H8-BINAP in THF (Figure S18c) is considered an upper limit of  T−T regarding (S)-H8-BINAP in film 2.     because internal conversion from S1 can be ignored for the chromophores in this manuscript.The fluorescence yield (Φ f ′ ) under weak excitation can be expressed as: )   where kf is the fluorescence rate constant from S1 and kisc is the rate constant of ISC from S1.However, an additional S1 quenching pathway, FRETS-T, occurs because the concentration of T1 increases under strong excitation.When we define the rate constant of FRETS-T as kFRET T-S, Φ f ′ under strong excitation (Φ f ) can be expressed as: and rapidly form S0 to depopulate T1. [S16] As proof that the PII also affects the saturation of  T 1 of film 2 under very large excitation intensity, the afterglow RTP image depleted by strong light irradiation at 445 nm, which does not contribute to S0-S1 excitation of (S)-BINAP, is irradiated (Figure S16b and S16c).If decrease of Ep/Ef with elevated excitation intensity (Figure 5a) is caused by FRETT-T, Ef of film 2 should also be saturated with increasing excitation irradiance for film 2 because RS-T and RT-T are not sufficiently different.However, such distinct saturation was selectively observed for phosphorescence in film 2 (Figure 5a).This also supports PII via T1 (Figure S16a) becoming a main triplet quenching pathway for excitation intensity greater than 30 mW cm -2 for film 2.However, the triplet saturation caused by FRETS-T and FRETT-T under strong excitation is greatly suppressed because of the significantly small εT-T, and this allows the continuous  T 1 accumulation of more than 1 wt%.Therefore, this report also quantitatively clarifies an additional point, demonstrating that the exploration of chromophores with small εT-T is necessary for brighter afterglow emission.The suppression of the PII via T1 is challenging but necessary to enhance  T 1 and achieve brighter afterglow RTP.

S18. Supporting movies
In Movie S1 and S2, an electron multiplication CCD camera (iXon Ultra/life 897, Andor Technology, United Kingdom) was used to capture the movies as tiff files.The CCD was cooled to −80 °C.In Movie S1 and S2, the setting condition regarding maximum brightness and minimum brightness of the tiff files was changed using ImageJ to appropriately compare the differences of each sample, as summarized in Table S3.In Table S3, the setting of the maximum brightness corresponds to the maximum intensity of the first two-dimensional images after excitation completely ceased.The setting of the minimum brightness corresponds to the background intensity caused by the heat-driven current.The tiff files were converted to AVI format using ImageJ without changing video parameters.

Movie S1.
A movie of afterglow images from an anticounterfeit media used in Figure 1d soon after excitation at 360 nm ceased.The intensity of the 360 nm beam is 0.1 mW cm - 2 .The size of the images is 400 µm × 400 µm.Images were used for (i) in Figure 1d.
Photonics, Meylan, France) and a 355 nm Q-switched microchip laser (PNV-M02510-1×0, Teem Photonics, Meylan, France).To measure T-T absorption of the film sample, a continuous-wave laser emitting at 360 nm (UV-F-360, CNI, Changchun, China) and UV-VIS-NIR light source (DT-MINI-2-GS, Ocean Optics, Tokyo, Japan) were used as the excitation and white probe light, respectively.A photonic multichannel analyzer (C10027-01, Hamamatsu Photonics) was used as a photodetector for the T-T absorption measurement.Optical setup of the transient absorption under contineous excitation is

Figure 4a .
Figure 4a.An objective lens (UPlanAPO ×10/0.40NA, Olympus) was used to obtain the images in the demonstration of Figure 1d.

Figure S4 .Figure S5 .
Figure S4.(a) Illustrations of a sample containing solid A and solid B on a glass substrate.(b) The irradiance-dependent appearance of high-resolution afterglow images of the sample.The images are taken in air by counting emission signals generated within 50 ms after ceasing the 360 nm excitation.

Figure S8 .
Figure S8.Relationship between the calculated T1-S0 energy (y-axis) and the peak wavelength of RTP (x-axis) for heavy-atom-free chromophores.Figure S20 in reference S5 shows data for the black plots.

Figure S10 .Figure S11 .
Figure S10.Determination of T1 concentration using transient absorption.(a) An optical setup for transient absorption.(b) Relationship between ΔAbs and excitation irradiance

Figure S12 .
Figure S12.Differences in triplet accumulation behavior between low (a) and high (b) guest concentrations.

Figure S14 .
Figure S14.Change in the depth profile of RTP intensity (T1 concentration) depending on different absorbances when excitation irradiance increases.(a) The T1 concentration profile along the depth direction of the film when absorbance of the film at the excitation wavelength is 0.1.(b) The relationship between RTP intensity and excitation irradiance when absorbance of the film at the excitation wavelength is 0.1.(c) The T1 concentration profile along the depth direction of the film when absorbance of the film at the excitation wavelength is 3.

Figure S15 .
Figure S15.Different relationships between afterglow RTP intensity and excitation intensity at 360 nm for two 1 wt% DPAF-doped amorphous β-estradiol films with different absorbance values at the excitation wavelength.

Figure S16 .
Figure S16.Transient absorption decay characteristics of (a) DPAF in degassed benzene at 640 nm and (b) benzophenone in degassed benzene at 532 nm.

Figure S17 .
Figure S17.Transient absorption decay characteristics of FIr6 in degassed THF at 440 nm and benzophenone in degassed benzene at 532 nm.

Figure S19 .
Figure S19.Analysis of small εT-T for the visible wavelengths using quantum chemical calculation.(a) Calculated oscillator strength of T-T absorption for DPAF (top) and (S)-BINAP (bottom).(b) Description of representative molecular orbitals related to the T-T transition with large oscillator strengths (f) of DPAF (left) and (S)-BINAP (right).

S12.
Potential mechanism by which FRETT-S lowers triplet generation yield Saturation behavior of fluorescence for DPAF in Figure 4a can be considered as deactivation caused by FRETS-T for the following reasons: when the excitation is weak, few T1 excitons exist near S1 states formed by excitation.In this situation, S1 excitons contribute to fluorescence and T1 generation via intersystem crossing (ISC) from S1 ) Therefore, Φ f decreases when FRETS-T occurs under strong excitation.A lower fluorescence yield was observed at saturation of the fluorescence at high excitation intensity, as shown in Figure 4a.Hence, the ratio of Φ f / Φ f ′ corresponds to  p ( ex )/ p ′ ( ex ) in Figure 4a [Φ f /Φ f ′ =  p ( ex )/ p ′ ( ex )]

Figure S20 .
Figure S20.Effect of photoinduced ionization in film 2. (a) Energy diagrams illustrating afterglow RTP depletion due to the photoinduced ionization (PII) under strong excitation irradiance.(b) Microscopic emission images of film 2 (i) under a 360 nm excitation irradiance, (ii) soon after the excitation ceased, (iii) under irradiation with a 445 nm beam,