Anthracene-incorporated cyanostilbene based donor–acceptor systems: intramolecular charge transfer and aggregation induced emission

Abstract

Cyanostilbene systems are highly attractive due to their fascinating fluorescence properties in the solid state. Herein, we report the synthesis and photophysical properties of highly emissive donor–acceptor systems based on anthracene and cyanostilbene, carrying hexyl (CSB-1) and dodecyl (CSB-2) chains. The molecules showed strong emission in the solution state attributed to the intramolecular charge transfer (ICT). The ICT band in these molecules showed a solvatochromic redshift with an increase in the dielectric constant of the solvents. The study explored the solid state emission properties of CSB-1 and compared them with that of dodecyloxy derivative CSB-2. Both CSB-1 and CSB-2 showed comparable emission in the solid state attributed to slipped molecular arrangement. Interestingly, the molecule CSB-1 showed a stimuli responsive dual mode luminescence switching under applied stress and ethyl acetate vapours. Owing to the rigid molecular packing, CSB-1 showed a higher quantum yield (ϕ_F = 0.43) in the solid state in comparison to polycrystalline CSB-2 (ϕ_F = 0.37). The analysis of the single crystal structural data of CSB-1 has shown that the molecules possess a twisted geometry and the adjacent molecular pair comprises J-aggregates, with arrangement along the molecular long axis. A comparative study of powder X-ray diffractograms showed that both CSB-1 and CSB-2 adopt similar molecular packing with different interplanar distances along the molecular long axis. Furthermore, this study substantiates the experimental results with TD-DFT calculations. The present study provides a detailed structure–property correlation of two novel compounds with the potential for various optoelectronic applications.