New fluorescent coumarin dyes containing functional acceptor groups: The investigation of photophysical, optical, and thermal properties

Nine novel coumarin-based compounds with a donor-π-acceptor system were synthesized, and their structural characterizations were determined by spectroscopic methods. The effects of different acceptor groups, such as dicyanovinyl, cyanoacrylic acid, and rhodanine-3-acetic acid at the 3-position of the coumarin ring, on the electronic and optical properties of the structure were investigated. Moreover, the coumarin structure was derived by adding an electron donor methoxy group, and a fused benzene ring, which also increases the planar structure. Synthesized compounds' absorption and emission properties are strongly influenced by substitution in the coumarin moiety. Four dyes showed near-IR emission in the solid state with green to orange fluorescence under UV light. The structural and electronic properties of the molecules were obtained with the DFT calculations at B3LYP/6-311++g(d,p) level of theory. The frontier molecular orbitals and the global reactivity descriptors were computed. Additionally, some DSSC parameters for 3a-c and 5a-c were also determined to provide insight into their potential. All compounds showed good thermal stability (Td > 200 °C).