Relationship between the structure and spectral-generation properties of coumarins benzopyrilium derivatives

The spectral and generation parameters of new coumarins – benzopyrylium derivatives – in ethanol and acetonitrile under coherent excitation were studied. It was shown that these compounds are bichromophores. Based on quantum chemical calculations, it was established that for all the studied compounds the ground state $(S_0)$ is characterized by an almost flat conformation of the aromatic part of their molecules. At the same time, the first excited state $(S_1)$ is characterized by rotation of the perilium fragment by a certain torsion angle. The spatial orientation of the molecular orbitals of the structural elements of the molecules under study, the dipole moments and oscillator strengths of the $S_1\to S_0$ electronic transition were determined. The relationship between these parameters and spectral and generation characteristics has been established. It has been shown that the nature of the substituents in the 6th and 7th positions of the coumarin backbone and benzopyrylium nucleus determines their lasing properties. Generation in the spectral region 715–740 nm was obtained using coumarin-class dyes.