engleski

Tuning the photophysics of two-arm bis[(dimethylamino)styryl]benzene derivatives by heterocyclic substitution

The identification of novel molecular systems with high fluorescence and significant NLO properties is a hot topic in the continuous search for new emissive probes. Here, the photobehavior of three two-arm bis[(dimethylamino)styryl]benzene derivatives, where the central benzene was replaced by a pyridine, a furan, or a thiophene, was studied by stationary and time-resolved spectroscopic techniques with ns and fs resolution. The three molecules under investigation all showed positive fluorosolvatochromism, due to intramolecular charge-transfer (ICT) dynamics from the electron- donor dimethylamino groups, and significant fluorescence quantum yields, because of the population of a planar and emissive ICT state stabilized by intramolecular hydrogen bonds. The NLO properties (hyperpolarizability coefficient and TPA cross-section) were also measured. The obtained results allowed the role of the central heteroaromatic ring to be disclosed. In particular, the introduction of the thiophene ring guarantees high fluorescent quantum yields irrespective of the polarity of the medium and the largest hyperpolarizability coefficient because of the increased conjugation. An important and structure-dependent involvement of the triplet state was also highlighted, with the intersystem crossing being competitive with fluorescence, especially in the thiophene derivative, where the triplet was found to significantly sensitize molecular oxygen also in a polar environment, for possible applications in photodynamic therapy.

fluorescence ; solvatochromism ; DFT quantum mechanical calculations ; nonlinear optical properties ; ultrafast spectroscopy ; intersystem crossing ; singlet oxygen sensitization

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