Effect of π-conjugated linkage on photophysical properties: Acetylene linker as the better connection group for highly solvatochromic probes

• The influence of the π-conjugated linker in the solvatochromism was evaluated.
• Acetylene linker improved the solvatochromism, Stokes shifts and photostability.
• The geometrical in the ground and excited state were analyzed by DFT and TD-DFT.

Fluorophores based in triphenylamine and fluorene (1–3) were synthetized and the effects of π-conjugated linkers (vinyl, ethynyl and 1,3-diynyl) on the solvatochromic properties were studied. The fluorescence emission spectra of the dyes were studied using solvents of different polarities, and the influence of specific solvent–solute interactions over emission properties was investigated through Lippert–Mataga model. In particular, we found that compound 2 (with an ethynyl group) exhibits significant advantages over compounds 1 and 3 with vinyl and 1,3-dynyl groups, respectively. It shows a better solvatochromism (140 nm from hexane to CH3CN), higher Stokes shifts (178 nm in CH3CN) and more sensitive quantum yields toward solvent polarity (0.09DMF–0.98THF), when compared with those to the reference probe (Prodan). Furthermore, this linker exhibits higher resistance against photodegratation under same conditions. The geometrical and electronic transitions were analyzed by DFT and TD-DFT, and the results are consistent with the experimental observations.

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