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Issue 38, 2019
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Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

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Abstract

Twisting of the acene backbone out of planarity in twisted acenes leads to a variation in their optical and electronic properties. The effect of increasing twist angles on the properties of the photoexcited triplet states of a series of anthracene-based helically tethered twisted acenes is investigated here by Electron Paramagnetic Resonance (EPR) spectroscopy. Increasing signal intensities with increasing twist angles indicate increased intersystem crossing efficiencies for the twisted molecules compared to the untethered reference compound. Variations in the electron spin polarisation observed in the transient EPR spectra, in particular for the compound with the shortest tether, imply changes in the sublevel population kinetics depending on molecular geometry. Changes in the zero-field splitting parameters and in the proton hyperfine couplings for compounds with short tethers and therefore higher twist angles point towards a slight redistribution of the spin density compared to the parent compound. The experimental results can be explained by considering both an increase in twist angle and a related decrease in the dihedral angle between the phenyl side groups and the acene core. The observation of a clear excitation-wavelength dependence suggests preferential excitation of different molecular conformations, with conformers characterised by higher twist angles selected at higher wavelengths.

Graphical abstract: Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

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Supplementary files

Article information


Submitted
24 Jul 2019
Accepted
14 Aug 2019
First published
20 Sep 2019

This article is Open Access

Phys. Chem. Chem. Phys., 2019,21, 21588-21595
Article type
Paper

Photoexcited triplet states of twisted acenes investigated by Electron Paramagnetic Resonance

C. E. Tait, A. Bedi, O. Gidron and J. Behrends, Phys. Chem. Chem. Phys., 2019, 21, 21588
DOI: 10.1039/C9CP04135D

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