V-Shaped Tröger Oligothiophenes Boost Triplet Formation by CT mediation and Symmetry Breaking
A new family of molecules obtained by coupling the Tröger’s base unit with dicyanovinylene-terminated oligothiophenes of different lengths has been synthesized and characterized by steady-state stationary and transient time-resolved spectroscopies. Quantum chemical calculations allow us to interpret and recognize the properties of the stationary excited states, as well as the time-dependent mechanisms of singlet-to-triplet coupling. The presence of the diazocine unit in the Tröger’s base derivatives is key to efficiently produce singlet-to-triplet intersystem crossing mediated by the role of the nitrogen atoms and of the almost orthogonal disposition of the two thiophene arms. Spin-orbit coupling mediated interstate ISC is activated by a symmetry breaking process in the first singlet excited state with a partial charge transfer character. This mechanism is characteristic of these molecular triads since the independent dicyano-vinylene oligothiophene branches do not display appreciable ISC. These results show how the Tröger’s base coupling of organic chromophores can be used to improve the ISC efficiency and tune their photophysics.
The authors thank the Spanish Ministry of Science and Innovation (projects MICIN/FEDER PID2021-127127NB-I00, PID2019-109555GB-I00, PID2022-136231NB-I00, PID2019-106268GB-C33 and TED2021-129886B-C43) and the Junta de Andalucía (PROYEXCEL-0328) and the Eusko Jaurlaritza (project PIBA19-0004). We also thank the Research Central Services (SCAI) of the University of Málaga for the access to the facilities. S.M.R thanks the Spanish Ministry of Universities and the University of Málaga for her Margarita Salas postdoctoral fellowship under the “Plan de Recuperación, Transformación y Resiliencia” funded by European Union-Next Generation EU. J. M. M. B. wants to acknowledge the Spanish University Ministry and the European Union for his Maria Zambrano fellowship with NextGen-Eu funding. D.C and C.T. are thankful for the technical and human support provided by DIPC Computer Center. C. T. is supported by DIPC and Gipuzkoa’s council joint program Women and Science. MJAN and FSB gratefully acknowledge Universidad Rey Juan Carlos for their postdoctoral and predoctoral contracts. The work is also supported by a National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (Grant 2021R1A2C3006308, 2021R1C1C1013828 and 2021R1A6A1A03039503). TMC would like to acknowledge support from EPSRC project EP/N026411/1.
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