Triplet Photosensitizers Research Articles

Visible Light-Induced and Singlet Oxygen-Mediated Photochemical Conversion of 4-Hydroxy-α-benzopyrones to 2-Hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides/carboxylates Using Rose Bengal as a Photosensitizer.

Development of a visible light-induced and singlet oxygen-mediated green protocol has been accomplished for the first time for the photochemical transformation of 4-hydroxy-α-benzopyrones to a new series of biorelevant 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides and 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates using rose bengal as a triplet photosensitizer at ambient temperature. Metal-free one-pot synthesis, broader substrate scope, good-to-excellent yields, use of cost-effective and eco-friendly starting materials and photosensitizer, and energy efficiency are the salient features of this newly developed method.

Visible-Light-Driven Triplet Sensitization of Polycyclic Aromatic Hydrocarbons Using Thionated Perinones.

Metal-free chromophores that efficiently generate triplet excited states represent promising alternatives with respect to transition metal-containing photosensitizers, such as those featuring metal-to-ligand charge transfer excited states. However, such molecular constructs have remained underexplored due to the unclear relationship(s) between molecular structure and efficient/rapid intersystem crossing. In this regard, we present a series of three thionated perinone chromophores serving as a newly conceived class of heavy metal-free triplet photosensitizers. We demonstrate that thionation of the lone C═O substituent in each highly fluorescent perinone imparts red-shifted absorbance bands that maintain intense extinction coefficients across the visible spectrum, as well as unusually efficient triplet excited state formation as inferred from the measured singlet O2 quantum yields at 1270 nm (ΦΔ = 0.78-1.0). Electronic structure calculations revealed the emergence of a low energy S1 (n → π*) excited state in the proximity of a slightly higher energy S2 (π → π*) excited state. The distinct character in each of the two lowest-lying singlet state manifolds resulted in the energetic inversion of the corresponding triplet excited states due to differences in electron exchange interactions. Rapid S1 → T1 intersystem crossing was thereby facilitated in this manner through spin-orbit coupling as predicted by the El Sayed rules. The lifetimes of the resultant triplet excited states persisted into the microsecond time regime, as measured by transient absorbance spectroscopy, enabling effective bimolecular triplet sensitization of some common polycyclic aromatic hydrocarbons. The synthetically facile interchange of a single O atom to an S atom in the investigated perinones resulted in marked changes to their photophysical properties, namely, conversion of dominant singlet state fluorescence in the former to long-lived triplet excited states in the latter. The combined results suggest a general strategy for accessing long-lived triplet excited states in organic chromophores featuring a lone C═O moiety residing within its structure, valuable for the design of metal-free triplet photosensitizers.

Long‐Lived Triplet Excited State Accessed with Spin–Orbit Charge Transfer Intersystem Crossing in Red Light‐Absorbing Phenoxazine‐Styryl BODIPY Electron Donor/Acceptor Dyads

Orthogonal phenoxazine‐styryl BODIPY compact electron donor/acceptor dyads were prepared as heavy atom‐free triplet photosensitizers (PSs) with strong red light absorption (ϵ=1.33×105 M−1 cm−1 at 630 nm), whereas the previously reported triplet photosensitizers based on the spin‐orbit charge transfer intersystem crossing (SOCT‐ISC) mechanism show absorption in a shorter wavelength range (<500 nm). More importantly, a long‐lived triplet state (τT=333 μs) was observed for the new dyads. In comparison, the triplet state lifetime of the same chromophore accessed with the conventional heavy atom effect (HAE) is much shorter (τT=1.8 μs). Long triplet state lifetime is beneficial to enhance electron or energy transfer, the primary photophysical processes in the application of triplet PSs. Our approach is based on SOCT‐ISC, without invoking of the HAE, which may shorten the triplet state lifetime. We used bisstyrylBodipy both as the electron acceptor and the visible light‐harvesting chromophore, which shows red‐light absorption. Femtosecond transient absorption spectra indicated the charge separation (109 ps) and SOCT‐ISC (charge recombination, CR; 2.3 ns) for BDP‐1. ISC efficiency of BDP‐1 was determined as ΦT=25 % (in toluene). The dyad BDP‐3 was used as triplet PS for triplet‐triplet annihilation upconversion (upconversion quantum yield ΦUC=1.5 %; anti‐Stokes shift is 5900 cm−1).

Bodipy-Phenylethynyl Anthracene Dyad: Spin-Orbit Charge Transfer Intersystem Crossing and Triplet Excited-State Equilibrium

Spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) is a promising method to design heavy atom-free triplet photosensitizers (PSs). Herein, a new organic triplet PS, BDP-An (Bodipy-phenylethynyl anthracene dyad) has been synthesized and studied. In polar solvents, charge transfer (CT) emission band was observed, and the singlet oxygen quantum yield (ΦΔ) is up to 95%. From femtosecond transient absorption (fs TA) spectra, SOCT-ISC mechanism was verified, the charge separation (CS) time takes1.6 ps, the lifetime of charge recombination (CR) is 3.8 ns, moreover the triplet state of phenylethynyl anthracene was also observed. In nanosecond transient absorption (ns TA) spectra, long-lived triplet states (τT =108 μs) were observed, which are delocalized on both parts of the dyad, i.e. there is a triplet excited-state equilibrium. This is the first report on the triplet excited-state equilibrium observed in an electron donor/acceptor dyad showing SOCT-ISC. With BDP-An as the triplet donor and perylene as the triplet acceptor, triplet-triplet annihilation upconversion (TTA UC) was performed, the upconversion quantum yield was up to 18.9%, and the lifetime of TTA-based delayed fluorescence was determined as 70.8 μs.

(Invited) Donor-Acceptor Systems from Triplet Photosensitizers for High Potential, Long-Lived Charge Separation

Generation of high potential, long-lived charge separated states in donor-acceptor systems are invaluable for converting light energy into either electricity or fuels. The majority of the donor-acceptor conjugates designed for this purpose are derived mainly from short-lived singlet sensitizers.1,2 In such conjugates, charge separation from the singlet excited donor or acceptor results in a short-lived charge separated state of singlet spin character. Alternatively, by utilizing high-energy triplet sensitizers one could generate long-lived charge separated states. The radical ion-pairs of triplet spin character slowly charge recombine to the ground state due to spin forbidden process. However, witnessing such a process purely from the triplet-excited state without the interference of the singlet excited state and other competing photochemical events such as excitation energy transfer has been challenging to establish.3-5 Here, we summarize our efforts to synthesize donor-acceptor conjugates bearing triplet sensitizers wherein excited state electron transfer exclusively occurs from the triplet excited state.3-6 To achieve the goal, two types of triplet sensitizers, viz., palladium and platinum porphyrins, and b-iodo functionalized BODIPYs are covalently linked to the well-known electron acceptor, fullerene, C60. Using femtosecond transient absorption studies covering wide temporal and spatial regions, and time-resolved electron paramagnetic studies, photoinduced electron transfer from 3MP* (M = Pd or Pt) to C60 in these dyads, leading to the formation of MP•+-C60 •- charge separated state of triplet spin character is demonstrated. Similarly, the role of triplet sensitizers in promoting charge separation in I2BODIPY-C60 and I2azaBODIPY-C60 dyads6 is also highlighted. 1. B. KC, F. D’Souza, Coord. Chem. Rev. 2016, 322, 104-141.2. D’Souza, and O. Ito ‘Chem. Soc. Rev. 2012, 41, 86-96.3. Obondi, G. N. Lim, F. D’Souza, J. Phys. Chem. C 2015, 119, 176-185.4. Obondi, G. N. Lim, B. Churchill, P. K. Poddutoori, A. van der Est, and F. D’Souza, Nanoscale, 2016, 8, 8333-8344.5. K. Poddutoori,Y. E. Kandrashkin, C. O. Obondi, F. D’Souza and A. van der Est, Phys. Chem. Chem. Phys. 2018, 20, 28223-28231.6. Shao, H. B. Gobeze, V. Bandi, C. Funk, B. Heine, M. J. Duffy, V. Nesterov, P. A. Karr, F. D’Souza, ChemPhotoChem, 2020, in press.

Efficient Photooxidation of Sulfides with Amidated Alloxazines as Heavy-atom-free Photosensitizers.

Photooxidation utilizing visible light, especially with naturally abundant O2 as the oxygen source, has been well-accepted as a sustainable and efficient procedure in organic synthesis. To ensure the intersystem crossing and triplet quantum yield for efficient photosensitization, we prepared amidated alloxazines (AAs) and investigated their photophysical properties and performance as heavy-atom-free triplet photosensitizers and compared with those of flavin (FL) and riboflavin tetraacetate (RFTA). Because of the difference in the framework structure of AAs and FL and the introduction of carbonyl moiety, the absorption of FL at ∼450 nm is blue-shifted to ∼380 nm and weakened (ε = 8.7 × 103 for FL to ∼6.8 × 103 M–1 cm–1), but the absorption at ∼340 nm is red-shifted to ∼350 nm and enhanced by ∼50% (from ε = 6.4 × 103 for FL to ∼9.9 × 103 M–1 cm–1) in AAs. The intersystem crossing rates from the S1 to T1 are also enhanced in these AAs derivatives, while the fluorescence quantum yield decreases from ∼30 to ∼7% for FL and AAs, respectively, making the triplet excited state lifetime and the singlet oxygen quantum yield of AAs at least comparable to those of FL and RFTA. We examined the performance of these heave-atom-free chromophores in the photooxidation of sulfides to afford sulfoxides. In accordance with the prolonged triplet excited state lifetime and enhanced triplet quantum yield, 2–5-fold performance enhancements were observed for AAs in the photooxidation of sulfides with respect to FL. We proposed that the key reactive oxygen species of AA-sensitized photooxidation are singlet oxygen and superoxide radical anion based on mechanistic investigations. The research highlights the superior performance of AAs in photocatalysis and would be helpful to rationalize the design of efficient heavy-atom-free organic photocatalysts.

Multifunctional Photosensitizing and Biotinylated Polystyrene Nanofiber Membranes/Composites for Binding of Biologically Active Compounds

A three-step postprocessing functionalization of pristine electrospun polystyrene nanofiber membranes was used for the preparation of nanostructured biotinylated materials with an externally bonded porphyrin photosensitizer. Subsequently, the material was able to strongly bind biologically active streptavidin derivatives while keeping its photosensitizing and antibacterial properties due to the generation of singlet oxygen under the exclusive control of visible light. The resulting multifunctional materials functionalized by a streptavidin-horseradish peroxidase conjugate as a model bioactive compound preserved its enzymatic activity even in the presence of a porphyrin photosensitizer with some quenching effect on the activity of the photosensitizer. Prolonged kinetics of both singlet oxygen luminescence and singlet oxygen-sensitized delayed fluorescence (SODF) were found after irradiation by visible light. The above results reflected less effective quenching of the porphyrin photosensitizer triplet state by ground state oxygen and indicated hindered oxygen transport (diffusion) due to surface functionalization. We found that SODF could be used as a valuable tool for optimizing photosensitizing efficiency as well as a tool for confirming surface functionalization. Full photosensitizing and enzyme activity could be achieved by a space separation of photosensitizers and enzyme/biomolecules in the nanofiber composites consisting of two layers. The upper layer contained a photosensitizer that generated antibacterial singlet oxygen upon irradiation by light, and the bottom layer retained enzymatic activity for biochemical reactions.

Electronic coupling and spin-orbit charge transfer intersystem crossing (SOCT-ISC) in compact BDP-carbazole dyads with different mutual orientations of the electron donor and acceptor.

In order to study the spin-orbit charge transfer induced intersystem crossing (SOCT-ISC), Bodipy (BDP)-carbazole (Cz) compact electron donor/acceptor dyads were prepared. Charge transfer (CT) emission bands were observed for dyads showing strong electronic coupling between the donor and the acceptor (coupling matrix elements VDA, 0.06 eV-0.18 eV). Depending on the coupling magnitude, the CT state of the dyads can be either dark or emissive. Equilibrium between the 1LE (locally excited) state and the 1CT state was confirmed by temperature-dependent fluorescence studies. Efficient ISC was observed for the dyads with Cz connected at the meso-position of the BDP. Interestingly, the dyad with non-orthogonal geometry shows the highest ISC efficiency (ΦΔ = 58%), which is different from the previous conclusion. The photo-induced charge separation (CS, time constant: 0.7 ps) and charge recombination (CR, ∼3.9 ns) were studied by femtosecond transient absorption spectroscopy. Nanosecond transient absorption spectroscopy indicated that the BDP-localized triplet state was exceptionally long-lived (602 µs). Using pulsed laser excited time-resolved electron paramagnetic resonance spectroscopy, the SOCT-ISC mechanism was confirmed, and we show that the electron spin polarization of the triplet state is highly dependent on the mutual orientation of the donor and acceptor. The dyads were used as triplet photosensitizers for triplet-triplet-annihilation (TTA) upconversion, and the quantum yield is up to 6.7%. TTA-based delayed fluorescence was observed for the dyads (τDF = 41.5 µs). The dyads were also used as potent photodynamic therapy reagents (light toxicity of IC50 = 0.1 µM and dark toxicity of IC50 = 70.8 µM).

Nanoscale Metal-Organic Frameworks and Metal-Organic Layers with Two-Photon-Excited Fluorescence.

Metal-organic frameworks (MOFs) based on 9,10-diphenylanthracene-derived ligands had been reported to exhibit upconverted fluorescence through triplet-triplet annihilation. We found that zirconium MOFs based on 9,10-diphenylanthracene can also give upconverted fluorescence via two-photon absorption without adding a triplet photosensitizer when a femtosecond pulsed laser is used as the excitation source. By tuning the synthetic condition, we obtained nanoscale MOFs of UiO structure in both octahedral and hexagonal nanoplate shapes, as well as a hexagonal nanoplate of MOFs of hcp-UiO structure and two-dimensional metal-organic layers. All of them, as well as a homogeneous solution of the 9,10-diphenylanthracene ligand, exhibit upconverted fluorescence upon excitation using a laser pulse of 60 fs with a pulse energy of ∼1.1 × 106 nJ/cm2 (unfocused). Moreover, we observed different emission spectra by two-photon excitation compared to those by one-photon excitation, which indicates access to a unique initial excited state via two-photon excitation. This phenomenon is not observed for a homogeneous solution of the ligand. These nanoscale MOFs may find application in two-photon fluorescence imaging.

Near‐IR‐Absorbing BODIPY‐5,10‐Dihydrophenazine Compact Electron Donor/Acceptor Dyads and Triads: Spin‐Orbit Charge Transfer Intersystem Crossing and Charge‐Transfer State

Abstract5,10‐dihydro‐5,10‐dimethylphenazine (PZ) and boron dipyrromethene (Bodipy) were linked to prepare compact electron donor/acceptor dyads and triads. The effect of the molecular geometry on the UV‐Vis absorption, fluorescence and the spin‐orbit charge transfer intersystem crossing (SOCT‐ISC) efficiency were studied. Interestingly, a broad near‐IR charge transfer (CT) absorption band (centred at 670 nm) was observed for the dyad/triad showing more coplanar geometry. Triplet state formation was observed in low polar solvents for the triad with orthogonal geometry (triplet state quantum yield is 30 % and lifetime is τT=210 μs). Femtosecond transient absorption spectra indicated fast charge separation (CS, 2 ps) and slow charge recombination (CR, &gt;1.5 ns). The low‐lying 3CT state of the dyads/triads in polar solvent (1.23 eV vs. the 1.65∼1.69 eV of the 3LE state) was confirmed by intermolecular triplet photosensitizing experiments and the spin density surface analysis. These results are useful for design of new broadband, near‐IR absorbing heavy atom‐free triplet photosensitizers.

Simultaneously High Upconversion Efficiency and Large Anti‐Stokes Shift by Using Os(II) Complex Dyad as Triplet Photosensitizer

AbstractTo extend the triplet lifetime of photosensitizer, two new osmium complex dyads, with Os(phen)3 as triplet energy donor and 9,10‐diphenylanthracene (DPA) as energy acceptor, namely Os(phen)3‐DPA and Os(phen)3‐BDPA, are synthesized and characterized. The triplet lifetime of Os(phen)3‐DPA dyad is significantly extended to 1.1 μs by introducing triplet energy acceptor DPA to activate the intramolecular triplet energy transfer from the Os(phen)3 to DPA units. By developing the triplet–triplet annihilation upconversion piars of Os(phen)3‐DPA and 9‐phenyl‐10‐(p‐tolyl)anthracene, the deep‐red light (at 663 nm) is upconverted to the blue‐violet emission (at 415 nm) in 1,2‐dichloroethane solution, and the highest upconversion quantum yield of 9.7% is achieved with a large anti‐Stokes shift of 1.12 eV.

Color-Tunable Delayed Fluorescence and Efficient Spin–Orbit Charge Transfer Intersystem Crossing in Compact Carbazole-Anthracene-Bodipy Triads Employing the Sequential Electron Transfer Approach

Spin–orbit charge transfer intersystem crossing (SOCT-ISC) is a promising approach to develop heavy-atom-free triplet photosensitizers. However, designing a strong visible-light harvesting heavy-atom-free triplet photosensitizer with efficient ISC ability in various solvents is still challenging. Most of the SOCT-ISC triplet photosensitizers exhibit efficient ISC only in solvent of particular polarity. To address this challenge, herein, two triads (BDP-AN-C-CZ and BDP-AN-N-CZ), composed of carbazole (CZ), anthracene (AN), and bodipy (BDP) moieties, were devised. In these triads, the distance, relative orientation, and position of CZ with respect to the AN moiety were varied to study the effect on photophysical properties, especially on SOCT-ISC efficiency. Electrochemical studies, steady-state, and time-resolved spectroscopies confirmed a sequential photoinduced electron transfer (PET) process in the triads. The fluorescence of the BDP moiety is quenched and a red-shifted CT emission band is observed in the triads, due to the enhanced PET effect, compared to the reference BDP-AN dyad. We observed that the SOCT-ISC yield can be enhanced taking advantage of sequential electron transfer. The triad BDP-AN-C-CZ, in which the CZ moiety was directly linked to the AN moiety, shows an efficient ISC ability both in low-polarity and high-polarity solvents, and unity triplet quantum yield (ΦT) was observed in dichloromethane. Femtosecond transient absorption spectroscopy confirmed the fast charge separation process (1.8 ps) in BDP-AN-C-CZ as compared to the other triad BDP-AN-N-CZ (4.8 ps) and the reference BDP-AN dyad (7.7 ps). The triads were used as triplet photosensitizers for triplet–triplet annihilation (TTA) upconversion, and high upconversion quantum yield (ΦUC = 18%) was observed. Interestingly, long-lived (τDF = 118 μs) and solvent-dependent color-tunable TTA delayed fluorescence was observed in the case of BDP-AN-C-CZ.

Novel BODIPY-bridged cyclotriphosphazenes.

Three new 2-component unsubstituted ( 4P ), diiodo- ( 5P ), and dibromo- ( 6P ) distyryl-BODIPY-bridged cyclotriphosphazene dimers were designed and synthesized. The newly synthesized BODIPY-cyclotriphosphazene systems were characterized by 1 H, 13 C, and 31 P NMR spectroscopy. The photophysical properties of the distryl-BODIPYs (4–6) and BODIPY-cyclotriphosphazene dyads ( 4P – 6P ) were studied by UV-Vis absorption and fluorescence emission spectroscopy. In these derivatives, the bino-type cyclotriphosphazene derivative bearing unsubstituted BODIPY unit 4P exhibited high fluorescence and no singlet oxygen generation due to the lack of spin converter. The attachment of heavy atoms (iodine and bromine) enabled the production of singlet oxygen. The bino-type BODIPY-cyclotriphosphazenes ( 5P and 6P ) were also used as triplet photosensitizers in the photooxidation of 1,3-diphenylisobenzofuran to endoperoxide via generation of the singlet oxygen in dichloromethane. The singlet oxygen production of these compounds was also investigated via a direct method and produced a singlet oxygen phosphorescence peak at 1270 nm.

Semiconductor Quantum Dots as Components of Photoactive Supramolecular Architectures.

Luminescent quantum dots (QDs) are colloidal semiconductor nanocrystals consisting of an inorganic core covered by a molecular layer of organic surfactants. Although QDs have been known for more than thirty years, they are still attracting the interest of researchers because of their unique size‐tunable optical and electrical properties arising from quantum confinement. Moreover, the controlled decoration of the QD surface with suitable molecular species enables the rational design of inorganic‐organic multicomponent architectures that can show a vast array of functionalities. This minireview highlights the recent progress in the use of surface‐modified QDs – in particular, those based on cadmium chalcogenides – as supramolecular platforms for light‐related applications such as optical sensing, triplet photosensitization, photocatalysis and phototherapy.

Halogen Bonding Facilitates Intersystem Crossing in Iodo-BODIPY Chromophores.

BODIPY chromophores can serve as organic-based triplet photosensitizers for a wide range of applications. To perform this function, the formation of the triplet state is critical, and a better understanding of how to modulate the formation of the triplet state could lead to further advances in BODIPY-based sensitizers for solar energy conversion and photodynamic therapy. In this work we investigate the ability of halogen bonding, a noncovalent solvent interaction, to facilitate intersystem crossing in a diiodo-BODIPY. Ultrafast transient absorption spectroscopy is applied to diiodo-BODIPY in the presence of pyridine-based halogen bonding solvent molecules to determine the rate constants for intersystem crossing. We find that halogen bonding facilitates the formation of the triplet state by increasing the intersystem crossing rate constant of diiodo-BODIPY. The results are interpreted in terms of the Marcus expression for intersystem crossing. Quantum chemical calculations show that halogen bonding acts to alter both the spin-orbit coupling terms and the relative energetics of the singlet and triplet states.

Solvent effects on triplet-triplet annihilation upconversion kinetics of perylene with a Bodipy-phenyl-C60 photosensitizer.

The solvent effect usually plays an important role in triplet-triplet annihilation (TTA) upconversion processes. In this work, we have studied the TTA upconversion kinetics of perylene with Bodipy-phenyl-C60 as the triplet photosensitizer in five solvents, 1,4-dioxane, dichlorobenzene, chlorobenzene, toluene, and tetrahydrofuran (THF). Although no significant solvent effect was observed in steady-state absorption and fluorescence emission spectra, the overall TTA upconversion quantum yields showed a profound dependence on solvent properties, i.e. 4.9% in 1,4-dioxane, 7.1% in dichlorobenzene, 6.7% in chlorobenzene, 4.6% in toluene, and 2.2% in THF (the maximum of 50%). Each elementary reaction step involved in the overall process was analyzed by applying femtosecond and nanosecond time-resolved transient absorption spectroscopy, revealing that the fluorescence emission of perylene was more significantly affected by the solvents in contrast to the other steps. Moreover, an extra intramolecular energy-transfer pathway of Bodipy-phenyl-C60 was found via the formation of charge-separated states in dichlorobenzene, chlorobenzene, and THF solvents, once being excited. These conclusions provide valuable clues to choose the most favorable solvent for the higher TTA upconversion efficiency in related applications.

Triplet photosensitizer-nanotube conjugates: synthesis, characterization and photochemistry of charge stabilizing, palladium porphyrin/carbon nanotube conjugates.

The ability of a triplet photosensitizer to generate long-lived charge separated states, in contrast to traditionally used singlet photosensitizers, in covalently functionalized single-walled carbon nanotube hybrids has been investigated. Enriched single-walled carbon nanotubes with two diameters, namely (6,5) and (7,6), were covalently modified to carry a charge-stabilizing triplet photosensitizer derived from a palladium porphyrin. The nanohybrids were fully characterized and the presence of intramolecular interactions between the porphyrin and nanotubes was established from various spectroscopic, imaging, electrochemical and thermochemical studies. Photoluminescence of palladium porphyrin was found to be quantitatively quenched in the presence of covalently appended SWCNTs and this quenching is due to excited state charge separation and has been established by femtosecond transient absorption studies. Owing to the presence of the triplet photosensitizer, the charge separated states lasted over 3 ns, i.e., much longer than those reported earlier for singlet photosensitizer-derived nanotube hybrids. The nanohybrids also exhibited efficient photocatalytic behavior in experiments involving electron pooling of one-electron reduced methyl viologen in the presence of a sacrificial electron donor. Higher yields of photoproducts were achieved from the present donor-acceptor nanohybrids when compared with those of singlet photosensitizer-derived nanohybrids, more so for (6,5) nanotube derived hybrids compared to (7,6) nanotube derived hybrids. The present findings highlight the importance of triplet photosensitizer derived nanohybrids in artificial photosynthesis of charge separation and photocatalytic applicatons.

Rigid axially symmetrical C60-BODIPY triplet photosensitizers: effect of bridge length on singlet oxygen generation

Two rigid axially symmetrical C60-BODIPY systems with different bridge lengths have been synthesized and the dyad with short bridge generates a higher quantum yield of singlet oxygen.

Bodipy Derivatives as Triplet Photosensitizers and the Related Intersystem Crossing Mechanisms.

Recently varieties of Bodipy derivatives showing intersystem crossing (ISC) have been reported as triplet photosensitizers, and the application of these compounds in photocatalysis, photodynamic therapy (PDT), and photon upconversion are promising. In this review we summarized the recent development in the area of Bodipy-derived triplet photosensitizers and discussed the molecular structural factors that enhance the ISC ability. The compounds are introduced based on their ISC mechanisms, which include the heavy atom effect, exciton coupling, charge recombination (CR)-induced ISC, using a spin converter and radical enhanced ISC. Some transition metal complexes containing Bodipy chromophores are also discussed. The applications of these new triplet photosensitizers in photodynamic therapy, photocatalysis, and photon upconversion are briefly commented on. We believe the study of new triplet photosensitizers and the application of these novel materials in the abovementioned areas will be blooming.

Visible‐Light‐Induced Di‐π‐Methane Rearrangement of Dibenzobarrelene Derivatives

AbstractIt is demonstrated that the di‐π‐methane (DPM) rearrangement of carbonyl‐substituted dibenzobarrelene (9,10‐dihydro‐9,10‐ethenoanthracene) derivatives is induced by visible‐light‐induced triplet photosensitization with Ir(ppy)3, Ir(dFppy)3 or 1‐butyl‐7,8‐dimethoxy‐3‐methylalloxazine as catalysts, whereas derivatives that lack carbonyl substituents are photoinert under these conditions. Notably, the products are formed almost quantitatively.