Insights into the solvents effect on spectral and photophysical properties of novel fluorescent heteroaromatic bis-peri-fused azoxonium cations

Perchlorates of novel fluorescent heteroaromatic bis-peri-fused azoxonium cations were prepared and thoroughly investigated with regard to their spectral and photophysical behaviour. Solvatochromic fluorescence properties of the compounds obtained are determined by intermolecular electrophilic-nucleophilic interactions of cations with solvent molecules. Gutmann's donor numbers correctly assess the solvent effect on the cation spectral characteristics. Perchlorates of bis-peri-fused azoxonium cations are effective fluorescent dyes characterized by the quantum yields reaching 0.67. Single-exponential fluorescence decay of the dyes is disturbed in the case of DMSO solvent possessing strong Electron-Pair-Donor properties and is accompanied by a sharp decrease of the fluorescence quantum yields. In this case coordinating interaction of the DMSO molecules with Electron-Pair Acceptor center of the cations leads to the appearance of an additional efficient non-radiative channel of the energy deactivation of the electronic excitation.