Wavelength-tunable fluorophores based on quinoline fused α-cyanovinyl derivatives: Synthesis, photophysics properties and imaging

[Display omitted] In this paper, we designed and synthesized six 6-substituted quinolines-fused α-cyanovinyl derivatives QM-1 ∼ 3 and QS-1 ∼ 3 through π-expansion system with “pull–push” systems. QM-1 ∼ 3 and QS-1 ∼ 3 have large absorption extinction coefficients. QM-1 ∼ 2 and QS-1 ∼ 2 (H-, CH3O–) showed blue/green fluorescence emission. However, QM-3/QS-3 ((CH2CH3)2N–) exhibited large bathochromic shifts in emission maxima of QM-3 (form 544 to 627 nm), QS-3 (from 570 to 668 nm), large stokes shifts and relatively high fluorescent quantum yields (ΦQM-3,max = 0.49, ΦQS-3,max = 0.25) in different polar solvents. The results of emission spectra in water/DMSO mixtures (λQM-3,max = 655 and λQS-3, max = 687 nm) and DFT calculations further proved that QM-3/QS-3 had a significant intramolecular charge transfer (ICT) process. Moreover, QM-3 and QS-3 were suitable for fluorescence bio-imaging.