Structure and conformational dynamics of the cyclopropanecarbaldehyde molecule in the ground (Sb0) and lowest excited (Tb1 and Sb1) electronic states

Abstract

The structure and conformational dynamics of nonrigid cyclopropanecarbaldehyde (CPCA) molecule in the ground (S 0 ) and lowest excited triplet (Т 1 ) and singlet (S 1 ) electronic states were calculated using the MP2, DFT, CASSCF, CASPT2, and CCSD quantum chemical methods. According to ab initio calculations, in the S 0 electronic state there are two symmetri cal (cis and trans) conformers of the CPCA molecule. Excitation of the CPCA molecule to the Т 1 and S 1 electronic states causes significant structural changes: carbonyl ССНО fragment becomes nonplanar, cyclopropane fragment rotates around the C-C bond, thus changing the relative positions of the formyl and cyclopropane fragments. Using sections of the potential energy surfaces (PES) of the CPCA molecule in the Т 1 and S 1 states, we calculated the torsion and inversion wave functions and vibrational transition energies. The results obtained suggest a strong coupling of the torsion and inversion motions in the Т 1 and S 1 excited states.Experimental and theoretical research of the struc ture of molecules with cyclopropyl substituents is of considerable interest because of unique physical and chemical properties of such systems. 1,2 A number of ex perimentally established properties of substituted cyclo propanes can be interpreted within the framework of the Walsh-Hoffmann model, 1-4 which provides an explana tion for the ability of the cyclopropyl moiety to con jugation with unsaturated substituents. However, in some cases the cyclopropyl fragments are more similar to alkyl rather than unsaturated substituents as regards the effect on the structure and properties of molecules. 1,2To develop molecular models with high predictive power, one should obtain and collect detailed informa tion on the structure and properties of molecules and chemical substances. The present work is a continuation of our systematic theoretical and experimental studies 5-7 on the structure and conformational dynamics of mol