Rapid synthesis of 4-alkynyl coumarins and tunable electronic properties of emission solvatochromic fluorophores

摘要

Novel fluorescent 4-alkynyl coumarins were rapidly and efficiently synthesized by Sonogashira coupling of readily accessible coumaryl triflates. The photophysical properties of the predominantly highly fluorescent compounds were experimentally studied by absorption and fluorescence spectroscopy and their electronic structure was rationalized by DFT and TD-DFT calculations using the PBEh1PBE functional. For certain consanguineous series structure-property relationships of the absorption and emission characteristics were established by Hammett-Taft correlations. Most interestingly, the energy levels of the underlying subchromophores can be electronically fine-tuned and addressed upon photonic excitation for placing donor substituents at the remote alkynyl terminus of the dyes.