Photophysical and Protonation Time Resolved Studies of Donor-Acceptor Branched Systems with Pyridine Acceptors

Abstract : A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues by means of ambient and low temperature steady state spectroscopy and fs to ns time resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors and acetylenic π bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed Intramolecular Charge Transfer state on the ps timescale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Förster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral towards the protonated species on the 1 ps timescale is revealed.
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Fotis Kournoutas, Kostas Seintis, Nikolaos Karakostas, Jiří Tydlitát, Sylvain Achelle, et al.. Photophysical and Protonation Time Resolved Studies of Donor-Acceptor Branched Systems with Pyridine Acceptors. Journal of Physical Chemistry A, American Chemical Society, 2018, ⟨10.1021/acs.jpca.8b08628⟩. ⟨hal-01952327⟩

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