A novel NIR violanthrone derivative with high electron-deficiency: effect of fluorescence on dicyanomethylene substitution

Near infrared (NIR) dyes attracted increasing interests in widely potential applications, such as fluorescent probe and living organism imaging, due to their low background signals from biomolecules, low light scattering and deep penetration, and low-cost excitation light sources. A novel NIR violanthrone derivative (VA-CN) with dicyanomethylene substitution was synthesized and fully characterized by ¹H NMR, ¹³C NMR, HRMS, and IR spectrometry. It is demonstrated that the original planar conformation of violanthrone ring (the nine fused benzene rings) becomes twisted and unsymmetrical upon the incorporation of two strong electron-withdrawing dicyanomethylene units. Photophysical, electrochemical performances as well as distinct solvatochromic effects were studied in detail. Considering the low reduction potential (−0.56 V vs NHE), VA-CN could be considered as a good electron acceptor due to the strong electron deficiency resulted from dicyanomethylene group. A distinct increase in fluorescence was observed with 30-fold enhancement upon the addition of n-butyl amine. The reversible fluorescence “off-on” shows that VA-CN might be served as a promising fluorescent sensor for electron-rich amines.