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

Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of chlorocarbazoles I a-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, tau(f) and tau(p), fluorescence and phosphorescence quantum yield, phi(f) and phi(p) have been measured in the same experimental conditions and from these data the radiative and the radiationless rate constants (k(0)(f), k(isc), k(f)(0)(77), k(isc)(77), k(p)(0) and k(nr)(0)) and the intersystem crossing quantum yield, phi(isc), 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 lambda(max)(abs) associated to the electronic transitions, the heat of formation of the chlorocarbazoles and the corresponding radical cation (DeltaH(f) and DeltaH(f)(RC)) and the adiabatic ionization potential (I-a) 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 (E-p/2). (C) 2002 Elsevier Science B.V. All rights reserved.