Effect of thiophene substitution on the intersystem crossing of arene photosensitizers

Abstract

The effect of thienyl substitution on the intersystem crossing (ISC) of a few arenes was studied using steady state and time-resolved transient absorption and emission spectroscopies, as well as DFT/TDDFT computations. We found that the phenyl and thienyl substituents generally induce red-shifted absorptions for the chromophores, and the DFT/TDDFT computations show that the red-shifted absorption and emission are due to the increased HOMO and the reduced LUMO energy levels. Nanosecond transient absorption spectra indicate the formation of a triplet state, the triplet state lifetime is up to 282 μs, and the singlet oxygen quantum yields (Φ) are up to 60%. DFT/TDDFT computations indicate that introducing the thienyl substituent alters the relative singlet/triplet excited state energy levels, and the energy level-matched S/T states are responsible for the enhanced ISC of the thienyl compounds. This information is useful for the design of heavy atom-free triplet photosensitizers and for the study of the fundamental photochemistry of organic compounds.

Revisiting the non-fluorescence of nitroaromatics: presumption versus reality

“…At the same time, one must remember that the sulfur atom of the thiophene ring can provide an additional energy dissipation channel through ISC, which should be considered. 79,80 Within these two basic structures, the increase in the number of thiophene rings leads to small bathochromic shifts of the absorption that are typical for polyene chromophores. In terms of the fluorescence properties, all compounds experience a red-shift of the emission maxima with increasing solvent polarity, indicating the formation of CT states.…”

Intersystem Crossing and Electron Spin Selectivity in Anthracene‐Naphthalimide Compact Electron Donor‐Acceptor Dyads Showing Different Geometry and Electronic Coupling Magnitudes

“…For both Ph-NI and Ph-An, the fluorescence intensity is almost solvent polarity-independent, which indicates that there is no significant intramolecular CT (ICT) feature for the emissive S 1 state, and the n-π* state is not significantly involved in the emission processes. [57] For dyads, the fluorescence intensity decreased significantly and the emission bands are red-shifting with increasing solvent polarity (Figure 4c and 4d), which is the typical feature of the emissive ICT S 1 state. [14,25] Other dyads showed similar phenomenon (Figure S30 in the Supporting Information).…”

Charge Transfer, Intersystem Crossing, and Electron Spin Dynamics in a Compact Perylenemonoimide-Phenoxazine Electron Donor–Acceptor Dyad

“…Some compact orthogonal dyads showing efficient SOCT-ISC have been reported. ,,− However, there are still some challenges for the investigation of SOCT-ISC; for instance, the chromophores used for SOCT-ISC are limited. The majority of the reported studies are focused on chromophores such as naphthaleneimide, , Bodipy, ,− rhodamine, , and perylene bisimide. , Perylene-3,4-dicarboximide (PMI) has been widely used in various fields of photochemistry. − Recently, we reported N -(2,6-diisopropylphenyl)-perylene-3,4-dicarboximide - phenothiazine ( PMI–PTZ ) dyads; moderate ISC was observed, and the singlet oxygen quantum yield (Φ Δ ) was 57%. Phenoxazine ( PXZ ), an analogue of PTZ except only one-atom variation, is a typical electron donor (oxidation potentials are 0.20 and 0.18 eV for PXZ and PTZ, respectively, vs Fc/Fc + ).…”

“…38,47,50−52 However, there are still some challenges for the investigation of SOCT-ISC; for instance, the chromophores used for SOCT-ISC are limited. The majority of the reported studies are focused on chromophores such as naphthaleneimide, 53,54 Bodipy, 48,55−57 rhodamine, 51,58 and perylene bisimide. 59,60 Perylene-3,4dicarboximide (PMI) has been widely used in various fields of photochemistry.…”