New efficient dyes for the red part of the lasing spectrum

An investigation was made of the spectral, fluorescence, and lasing characteristics of two compounds of benzopyran derivatives with a condensed benzimidazole ring that emit in the 610–660 nm range under flashlamp excitation. The efficiency and photostability of the synthesized derivatives were several times better than those of the known xanthene dyes rhodamine C and rhodamine 101. Quantum chemical calculations using the π electron approximation were used to estimate the localization of the electronic excitations in molecular fragments.