Tuning photophysical properties of triphenylamine and aromatic cyano conjugate-based wavelength-shifting compounds by manipulating intramolecular charge transfer strength

A series of triphenylamine-based aromatic cyano compounds have been synthesized as red-emitting fluorophores with large Stokes shifts in both solution (>100 nm in CHCl3) and solid state (>150 nm in film). Intramolecular charge transfer (ICT) properties of the synthesized compounds are examined using UV–Vis absorptions, photoluminescence measurements and solvatochromic studies. Our studies suggest that Stokes shifts of these compounds can be fine-tuned by manipulating the ICT strength between donor and acceptor with various electronic donating groups, and the largest Stokes shifts are typically associated with compounds that have the strong ICT characters. The observed spectroscopic properties of the compounds are consistent with theoretical calculations using density function theory (DFT) or time-dependent density function theory (TD-DFT). The calculations suggest that the ICT occurs from localized HOMO to localized LUMO with magnitudes of 60–80%. The relative quantum yields of these fluorophores in solution are various and highly solvent dependent. In solid state, the quantum yields of the compounds are significantly increased and some can reach to 0.40.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The triphenylamine-based aromatic cyano fluorophores were synthesized as wavelength-shifting materials. ► They show specific spectral properties with absorbance from UV to 550 nm and emission around 600 nm. ► Large Stokes shifts were due to the strong intramolecular charge transfer (ICT) effect during excitation. ► The Stokes shift can be fine-tuned by the ICT character between different donor and acceptor groups. ► Solid state spectra were studied.