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

Abstract

Abstract Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of chlorocarbazoles 1a–e, 2a–b, 3a, 4a–b, 5a, 6a, 7a, 8a–c, 9a and 9b in acetonitrile and in solid matrix have been recorded at 298 and 77 K. The dynamic properties of the lowest excited singlet and triplet states in term of fluorescence and phosphorescence lifetime, τf and τp, fluorescence and phosphorescence quantum yield, φf and φp have been measured in the same experimental conditions and 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 derived. The intramolecular heavy atom effect (HAE) on the spectroscopic data and photophysical rate constant was analyzed and the incorporation of chlorine atoms to the carbazole moiety proved their ability to quench the fluorescence emission by spin-orbital coupling. The values of the HOMO and LUMO energy, the oscillator strength (f) and the λmax(abs) associated to the electronic transitions, the heat of formation of the chlorocarbazoles and the corresponding radical cation (ΔHf and ΔHf(RC)) and the adiabatic ionization potential (Ia) were also calculated by using the semiempirical PM3 method after HF/3-21G geometrical optimization, and were compared with the spectroscopic and photophysical data as well as with the one electron oxidation potential data (Ep/2).