Ultrafast Charge Transfer in Donor-TCBD/DCNQ-Donor-C 60 Multimodular Constructs

Light-induced electron transfer is a key step in solar energy conversion and is of myriad relevance in the fields of artificial photosynthesis, photocatalysis, photoconductivity, nonlinear optics, and molecular photovoltaics. For this, regulating the lifetimes of charge-separated states is paramount to building the next generation of light-energy-harvesting devices. In a donor-acceptor (D-A) system, light absorption by a chromophore results in the formation of an excited state species, followed by a charge transfer between an electron donor (D) and an electron acceptor (A), leading to a charge-separated D .+ -A .- species.The optimization of these processes and the understanding of their mutual interplay is ultimately aimed at achieving charge-separated species. As part of our continued effort in this field of strongly coupled donor-acceptor push-pull systems, 1-7 we recently reported on the synthesis of a new class of push-pull systems. 8 Here, using Sonogashira cross-coupling, [2 + 2] cycloaddition–retroelectrocyclization and 1,3-dipolar cycloaddition reaction, and phenothiazine (PTZ) as donor, and fullerene (C 60 ), tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) unit as acceptors, a novel series of multi-modular donor-acceptor conjugates was synthesized (top structures in the Figure). 8 Systematic studies using a suite of physico-chemical techniques and the ultrafast pump-probe spectroscopic methods reveal that the presence of C 60 modulates ultrafast charge-transfer events, ultimately resulting in charge-separated states with appreciable lifetimes. Importantly, C 60 acted as a terminal electron acceptor despite its greater reduction potential. In the present study, we have expanded the library of compounds and report a new series of push-pull multimodular systems (bottom structures in the Figure) featuring terminal triphenylamine (TPA) instead of phenothiazine, and showcase the key findings. Khan, Y. Jang, Y. Patil, R. Misra, and F. D’Souza, Angew. Chem. Int. Ed. 2021 , 60 , 20518–20527. S. Yadav, A. Z. Alsaleh,R. Misra, F. D’Souza, Chem. Sci . 2021 , 12 , 1109-1120. Pinjari, A. Z. Alsaleh,Y. Patil, R. Misra, F. D’Souza, Angew. Chem. Int. Ed . 2020 , 59 , 23697-23705. Sekaran, A. Dawson, Y. Jang, K. V. MohanSingh, R. Misra, F. D’Souza , Chem. Eur. J . 2021 , 27 , 14335-14344. Das, S.; Rout, Y.; Poddar, M.; Alsaleh, A. Z.; Misra, R.; D'Souza, F. Chem. Eur. J . 2024 , 30 , e202401959 Gupta, P. K.; Das, S.; Misra, R.;D’Souza, F. Chem. Eur. J ., 2024 , 30 , e202304313. Yadav, I. S.; Kaswan, R. R.; Liyanage, A.; Misra, R.; D’Souza, F. J. Phys. Chem. C 2024 , 128 , 4934-4945. Gupta, P. K., Ileperuma, C. V., Misra, R., D’Souza, F. Chem. Sci . 2025 , 16 , 12122. Figure 1