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Photophysical properties and immobilisation of fluorescent aminated benzimidazo[1, 2-a]quinolines

One of the most extensively studied classes of organic fluorescent sensors is that based on heterocyclic compounds. Benzimidazoles are widely incorporated in the structure of numerous biologically important natural and synthetic biochemical agents. Due to the possession of a highly conjugated planar chromophore, their benzannulated derivatives, offer promising applications in optoelectronics, optical lasers, fluorescence probes and organic luminophores [1]. The fluorescence of cyclic derivatives can be significantly altered by additional substituents placed on different positions of the planar chromophore or by condensation with other heterocycles, which leads to the extension of the conjugated aromatic surface [2]. Within this work, amino substituted benzimidazo[1, 2-a]quinolones were designed as fluorescence sensors to determine pH changes over a wide pH scale. The studied benzimidazo[1, 2-a]quinolines enable internal charge transfer (ICT) interactions, causing expressed pH sensing properties. It is proven that substituent on the position 5 of tetracyclic skeleton radically disrupt charge transfer within the aromatic core and significantly decrease fluorescence intensity. Moreover, upon acidification, the push - pull character of the ICT transition is enhanced in all aminated fluorescent dyes. The emission band is batochromiclly shifted and fluorescence is quenched. Computational analysis complemented experimental results by elucidating pKa values of investigated systems, thus aided in the determination of protonation forms present in solution during measurement and interpretation of electronic transitions.

benzimidazol[1, 2-a]quinolines ; photophysical properties ; fluorescence ; pH sensors

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