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Photobehavior and Nonlinear Optical Properties of Push–Pull, Symmetrical, and Highly Fluorescent Benzothiadiazole Derivatives

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journal contribution
posted on 30.09.2016, 00:00 by Federica Ricci, Fausto Elisei, Paolo Foggi, Assunta Marrocchi, Anna Spalletti, Benedetta Carlotti
Three quadrupolar D−π–A−π–D compounds, bearing alkoxy phenyls as mild electron donors and a benzothiadiazole (A), two benzothiadiazoles (B), or a benzothiadiazole linked to two thiophenes (C) as the acceptor units, are collectively the object of this study. They proved to be efficient yellow/orange/red fluorophores, respectively, with fluorescence being their preferred deactivation pathway. These systems exhibited positive fluorosolvatochromism and a noticeable decrease of the fluorescence quantum yield in the most polar solvent (with the quenching following the trend B > A > C). These findings point to an intramolecular charge transfer (ICT) nature of the emitting state, whose photoinduced dynamics was investigated by femtosecond-resolved transient absorption and fluorescence upconversion. Remarkable values of hyperpolarizability were estimated by the solvatochromic method. The significant two-photon absorption cross sections measured for AC (whose trend nicely parallels that of ICT efficiency), coupled with the intense emission, make them promising for applications as environment-sensitive probes in two-photon excited fluorescence imaging.