Novel emissive styryl dyes from 9-methoxy anthracene: Synthesis, photophysical, thermal stability, viscosity, and DFT...

Novel styryl colorants based on anchoring methoxy with anthracene as a donor linked with various active methylene acceptor groups to derive a conjugated π-system along with push-pull geometry were synthesized and well characterized. Photophysical properties were studied in different polarity solvents. The impact of solvent polarizability is delivered in redshifts in absorption and emission spectra, in addition to enhancing the quantum yield. The benzoxazole and benzimidazole moieties in 4c and 4d demonstrated heat stability of more than 300 °C. Fluorescent intensity is directly proportional to the viscosity and 4a demonstrates a notable viscosity sensor through 1.36 fold increase in intensity. In comparison to other styryl dyes, 4c and 4d were shown to have higher values in DMSO for polarizability (53.3496 × 10^-24 esu and 53.7459 × 10^-24 esu) and first-order hyperpolarizability (86.3467 × 10^-30 esu and 89.1941 × 10^-30 esu) as well as second-order hyperpolarizability (1768.9121 × 10^-36 esu and 1740.6940 × 10^-36 esu) due to presence of heterocyclic character. NLO properties of all the styryl dyes 4a-4e are within the fundamental boundary limits. The 4d (benzoxazole) dye exhibited a small HOMO-LUMO energy gap of 2.8825 eV, whereas the 4b and 4e dyes had a larger band gap due to the presence of a carbonyl group.