Density functional theory study of electronic structure and spectra of tetraoxa[8]circulenes

The electronic structure and spectra of a series of tetraoxa[8]circulene derivatives are studied by the density functional theory (DFT) calculations. The vertical transitions to the 30 lowest electronic excited states of the studied dyes are calculated by the time dependent (TD) DFT method in vacuum and solvent. The orbital nature and intensity of all observed absorption bands including vibronic satellites in the spectra of studied tetraoxa[8]circulene derivatives are explained. The reduction potentials are compared with electrochemical measurements and found to be relatively unaffected by the nature of the tetraoxa[8]circulene derivatives. We also obtained a good agreement between experimental fluorescence spectral characteristics of the tetraoxa[8]circulenes family and the theoretical analysis of the lowest singlet excited states wavefunctions. The nature of the fluorescent bands in the emission spectra is rather different for the generic tetraoxa[8]circulene and for its derivatives which agrees with the measured quantum yields and lifetimes. The 0–0 line of phosphorescence of the tetraoxa[8]circulene molecule (3A2g → X1A1g) is predicted at 533 nm.