Molecular Design Strategy for High-Yield and Long-Lived Individual Doubled Triplet Excitons through Intramolecular Singlet Fission

Abstract

Multi-exciton generation of organic chromophores, i.e., singlet fission (SF), is highly promising for photoenergy conversion such as photocatalysis and photovoltaics. Among the reported high-yield SF systems, many systems possess only short-lived triplet excited states derived from correlated triplet pair intermediates, but not individual doubled triplet excitons. However, high-yield and long-lived individual triplet exciton generation is favorable for achieving efficient photoenergy conversion. In this Focus Review, we discuss the molecular design strategy for high-yield and long-lived individual triplet exciton generation through intramolecular SF utilizing a series of acene derivatives such as hexacene, pentacene, and tetracene. In addition to clarifying the structural and vibronic characters required for high-yield individual triplet exciton generation, specific examples of the photoenergy conversion far exceeding 100% quantum yields of subsequent electron-transfer products and singlet oxygen generation are presented.

Triplet–Triplet Annihilation via the Triplet Channel in Crystalline 9,10-Diphenylanthracene

“…Thus, the observed peaks at magnetic field strengths equal to 3 J and 6 J and the dip at 4 J can be explained by coexistence of S-channel and T-channel TTA in the DPA crystal. Similar magnetic field effects on the yield of the excited triplet state were also observed in a covalently linked terylene-3,4:11,12-bis­(dicarboximide), in which singlet fission occurs efficiently upon photoexcitation. , The observed result was also discussed in terms of T-channel TTA.…”

“…Similar magnetic field effects on the yield of the excited triplet state were also observed in a covalently linked terylene-3,4:11,12-bis(dicarboximide), in which singlet fission occurs efficiently upon photoexcita- tion. 50,51 The observed result was also discussed in terms of Tchannel TTA.…”

Energy Versus Electron Transfer: Managing Excited-State Interactions in Perovskite Nanocrystal–Molecular Hybrids

“…Thus, modulation of these excited states of molecular sensitizers and surface states in semiconductor nanocrystals becomes important in designing light harvesting assemblies . An important application of such semiconductor-sensitizer hybrid assemblies is to initiate transfer of singlet or triplet energy from the excited semiconductor to molecular sensitizers. − In addition, one can also consider singlet fission of an excited sensitizer molecule to produce two triplet states and further transfer energy to another acceptor molecule. − The triplet excited states are attractive because they can induce energy upconversion through recombination of two triplets . Depending upon the device criteria one can select molecules with appropriate energy levels and/or redox levels to modulate excited-state events in sequence and maximize photon-harvesting efficiency through these assemblies.…”

Tuning Excited-State Energy Transfer for Light Energy Conversion: A Virtual Issue

“…Investigations in tetracene dimers revealed that conformational flexibility between adjacent tetracene units contributes significantly to the suppressed TT deactivation process through weakened electronic coupling, thus increasing the lifetime of triplets. 24 Khan, Laquai, and co-workers have demonstrated that poly[bis(4-phenyl)-(2,4,6-trimethylphenyl)amine] (PTAA) as a hole-transport layer outperforms nickel oxide owing to the reduced non-radiative recombination, which is indicative of lower interfacial trap state density. 25 Compared to the neat MAPbI 3 samples, the ground-state bleach of MAPbI 3 /PTAA exhibits a faster decay, which is attributed to the extraction of holes to the PTAA transport layer.…”

“…The triplet harvesting in the MX-generating SF is hindered by the direct deactivation process of a correlated triplet pair (TT). Investigations in tetracene dimers revealed that conformational flexibility between adjacent tetracene units contributes significantly to the suppressed TT deactivation process through weakened electronic coupling, thus increasing the lifetime of triplets …”