Electronic spectroscopy of carbazole and N- and C-substituted carbazoles in homogeneous media and in solid matrix

The dynamic properties of the lowest excited singlet and triplet states in terms of fluorescence and phosphorescence lifetime, τf and τp, fluorescence and phosphorescence quantum yield, φf and φp, for carbazole and N- and C-substituted carbazoles have been measured in organic solutions of different polarity and in solid matrix, at 298 and at 77 K, respectively. From these data, the radiative and the radiationless rate constants (kf0, kisc, kf0(77), kisc(77), kp0 and knr0) and the intersystem crossing quantum yield, φisc, were easily derived. Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of carbazole and carbazole derivatives have been recorded at 298 and at 77 K and the solvent and substituent effects on the spectroscopic data and on the photophysical rate constant have also been analyzed and good linear correlations have been obtained. The values of the HOMO and LUMO energy, the oscillator strength (f), the transition dipole (Δμ) and the wavelengths associated to the electronic transitions, the heat of formation of the carbazoles and the corresponding radical cations (ΔHf and ΔHf(RC)) and the adiabatic ionization potential (Ia) were calculated by using the semiempirical PM3 and ZINDO/S methods and were compared with the spectroscopic and photophysical parameters obtained as well as with the one-electron oxidation potential data (Ep/2) reported for the carbazole series.