Excited state dynamics of a model asymmetric molecular rotor: A five-dimensional study on 2-cyclopentylidene-tetrahydrofuran

The excited state dynamics of 2-cyclopentylidene-tetrahydrofuran (CPTHF) is investigated using quantum dynamics. CPTHF can be considered a model for an asymmetric molecular rotor in which unidirectional rotation could be triggered around the double bond. After excitation, conical intersections at twisted angles allow for rationless decay to the ground state. Two-dimensional potential energy surfaces for the ground and first (pi pi*) excited state have been calculated using CASSCF. They include the torsion around the double bond and the pyramidalisation at one carbon atom. The relaxation of CPTHF after photo-excitation has been then studied using up to five degrees of freedom. 2D wavepacket propagations on the explicit PESs do not allow the dissipation of the energy of the system after excitation. The inclusion of further modes, studied using the MCTDH method, show that the internal conversion rate is significantly altered depending on the modes included. (C) 2010 Elsevier B.V. All rights reserved.