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Nitro End Groups Remarkable Vibrational Reporters for Charge Transfer in the Excited States of Oligo(p-phenyleneethynylene)-Bridged Donor-Acceptor Dyads

Abstract : The D-π-A dyads [(n-Hex)2N(1,4-C6H4)]CC[(1,4-C6H4)NO2] (1) and [(n-Hex)2N(1,4-C6H4)]CC(1,4-C6H4)CC[(1,4-C6H4)NO2] (2) have been studied by ultrafast time-resolved infrared absorption spectroscopy. After excitation into their singlet charge-transfer (1CT) state, a fast decay (ca. 6 ps for 1 and 1 ps for 2) of the initially populated singlet state into a ground state (major pathway) and a longer lived excited state (possibly the triplet state) is observed. The nitro and alkyne groups were used as vibrational reporters to probe the changes induced by the charge-transfer process. For the first time, we confirm experimentally that these changes are consistent with expectations based on the traditional valence-bond representations of the CT states of these push-pull chromophores. An almost identical charge transfer takes place in the two dyads, despite π-bridges of different lengths between the donor and acceptor groups. Complementary DFT calculations support the experimental assignments and have helped clarify the photophysical behavior of 1 and 2.
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Submitted on : Monday, June 15, 2020 - 12:21:42 PM
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J. Kubicki, Maciej Lorenc, P. Cochelin, O. Mongin, A. Amar, et al.. Nitro End Groups Remarkable Vibrational Reporters for Charge Transfer in the Excited States of Oligo(p-phenyleneethynylene)-Bridged Donor-Acceptor Dyads. Journal of Physical Chemistry C, American Chemical Society, 2020, 124 (18), pp.9755-9764. ⟨10.1021/acs.jpcc.0c01532⟩. ⟨hal-02862821⟩

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