Design, synthesis and properties of twisted D-A-D’ arylamine derivatives with solvatochromism

In this study, three molecules with distorted asymmetric D-A-D' structure were synthesized by one-step nucleophilic substitution reaction using different fluorophores (carbazole, phenoxazine, phenothiazine) as electron donors and benzophenone with distorted conformation as electron acceptor. The target compounds were all confirmed by 1H NMR, 13C NMR and EI-MS. In addition, the molecular skeleton of the target compound containing a phenothiazine donor group was further confirmed by X-ray single-crystal diffraction analysis. Combined with the results of UV–vis absorption spectra and fluorescence emission spectra, we found that the different electron donating ability of donor parts (carbazole, phenoxazine and phenothiazine) led to the blue, green and light yellow fluorescence of these compounds in the solid states. Subsequent studies showed that these three compounds all showed remarkable solvatochromism in different organic solvent due to the intramolecular charge transfer (ICT) effect, and the increase of solvent polarity induces a red-shift in the emission wavelength. The results of mechanochromic properties confirmed that only the compound containing phenothiazine fluorophore showed obvious reversible mechanochromic properties. Compounds containing carbazole and phenothiazine groups showed aggregation-induced enhanced emission (AIEE), while compound bearing phenoxazine showed typical aggregation-induced emission (AIE) behavior. Through powder X-ray diffraction (XRD) analysis experiment, crystal structure analysis and theoretical calculation, the relationship between the structure and properties of these molecules was discussed. Finally, we also preliminarily explored the application of these molecules in biological imaging, which exhibited excellent biocompatibility and cell permeability in living cells. In brief, through reasonable molecular design, the luminescent properties and solvatochromism properties of these compounds can be regulated, which provides a theoretical basis for the rational design of molecules with excellent photophysical properties.