Rod-shaped Cyanoacrylic Derivatives with D-π-A Architecture: Synthesis, Thermal, Photophysical and Theoretical Studies

Two dyes, 4 and 5, bearing an alkoxy group as a donor connected to cyanoacrylic acid acceptor/anchoring group bridged by the phenylacetylene unit were designed and synthetised through Knoevenagel condensation between aromatic aldehydes and cyanoacetic acid reagent. The dyes were characterised using FT-IR, H-1-NMR, C-13-NMR, ESI-HRMS and polarised optical microscopy, absorption and fluorescence techniques. Nematic mesophase was identified for both rod-shaped dyes. During heating at high temperatures (>200 degrees C), the dyes exhibited marked thermal instability which resulted in material decomposition. The photophysical properties of the compounds were investigated in chloroform as well as their absorption, emission spectra in solid state. Solvatochromism was analysed and the mechanism of fluorescence quenching was performed using fullerene pyrrolidine tris-acid ethyl ester PyC60 as a receptor. The fluorescence quenching studies suggested charge transfer process from dyes 4 and 5 to PyC60, where the bimolecular rate constant k(q) was larger for 4 than 5, showing that the phenyl group performed better than the naphthyl group. The energy band gap predicted with DFT calculations agreed with the experimental data. Natural transition orbitals (NTOs) analysis revealed that S-1 states for 4 and 5 in gas phase have a predominantly local-excitation (LE) nature.