Conformational Mobility of 4,4′-Bisdimethyl-Aminobenzophenone in the Excited State

Abstract

Quantum-chemical calculations on various conformational states of the molecule of Michler's ketone have been carried out by semi-empirical and non-empirical methods (HyperChem 7.0 suite of programs and Gaussian 98). The influence of solvation on the relative levels of different orbital types and on the spin states of the molecule has been examined. The possibility of the TICT process occurring in polar media, which may have an important effect on the spectral characteristics of Michler's ketone, has been investigated.Key words: Michler's ketone, the TICT process, solvation energy, the PM3 method.Benzophenone and its amino-derivatives are used in industry as additives in polymerization mixtures as photo-initiators of polymerization. One example of this class of chromophore is 4,4¢-bisdimethylaminobenzophenone (also known as Michler's ketone, (MK)):the reactivity and spectral characteristics of which have been the subjects of a number of experimental studies [1-6]. Interpretation of the results of these studies has been proposed in terms of the formation of several conformers in the ground state and structural relaxation of the molecule on excitation, or the creation on excitation of a TICT state (twisted intramolecular charge transfer, i.e., a twisted state with intramolecular charge transfer). Literature results [3] may also indicate the formation of complexes of MK with solvent molecules.The problem of determining the nature of the luminescence and establishing the nature of the effect of a solvent on it also exists for other conformationally mobile molecules containing amino groups. One method for solving this problem is to use quantum-chemical analysis of the spectral properties of the chromophores. In particular, the results of such calculations indicate that the TICT state arises in the chromophores. But there are papers (e.g., see [7]) in which calculations do not confirm that the TICT process occurs in excited molecules, which the experimenters attribute a highly polar structure. Similar calculations have not yet been carried out for MK. In this study we have carried out quantum-chemical calculations on the energetic parameters of MK, the results of which have been compared with spectral data. 1980040-5760/05/4103-0198

Spectroscopic Studies of Dual Fluorescence in 2-((4-Fluorophenyl)amino)-5-(2,4-dihydroxybenzeno)-1,3,4-thiadiazole

“…The TICT model introduced in the seventies by K. Rotkiewicz, K. H. Grellmann, and Z. R. Grabowski, despite their different views on its mechanism, has become one of the best-known models in experimental and theoretical investigations in photophysics and molecular spectroscopy. Another equally interesting and highly popular approach in explaining the dual fluorescence phenomenon is the excited-state intramolecular proton transfer called ESIPT. ,− This effect was observed for organic molecules, in which the acceptor group is located in close proximity to the proton donor group. These processes of intramolecular proton transfer by excitation states have been a focus of many experimental and theoretical investigations as well. − …”