121st General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Scholars in Physical Chemistry
Room No. Room 402
Time THU 09:12-:
Code PHYS.O-2
Subject Photoinduced Symmetry-Breaking Charge Transfer Dynamics of 9,9'-Bianthracene
Authors Changmin Lee, Cheol Ho Choi1,*, Taiha Joo*
Department of Chemistry, Pohang University of Science and Technology, Korea
1Department of Chemistry, Kyungpook National University, Korea
Abstract 9,9’-Bianthracene (BA) is a representative model system of the symmetry-breaking charge transfer (SBCT). BA consists of two anthracene rings linked by a sigma bond. Upon photoexcitation, only one anthracene ring is excited, and this stated is called locally excited (LE) state. In polar solvents, a further reaction occurs to form charge transfer (CT) state.
Time-resolved fluorescence (TF) spectra of BA in heptane, acetonitrile, ethanol, and acetone were obtained. By analyzing the spectra, it was found that the CT reaction time was identical to the rotational solvation rate. High-resolution TF was obtained in acetonitrile solvents, and coherent nuclear motion of 40 cm-1 and 500 cm-1 were observed. Excited-state quantum mechanics/effective fragment potential molecular dynamics (QM/EFP MD) simulation to track the S1 state was performed for 65 Franck-Condon (FC) points which were made from the ground state equilibration process. As a result, the formation of the CT state was observed in almost all FC points. The electric field at the center of BA molecule was grown similarly to the reaction itself. We obtained the nuclear geometry with respect to time from the simulation results to analyze the geometrical change during the reaction. The torsional motion between two anthracene rings and the stretching motion of the central C-C bond was observed to be relevant to the CT reaction. These two motions well corresponded to the observed coherent nuclear wave packet, 40 cm-1, and 500 cm-1, respectively.
The CT reaction of BA is entirely coupled to the rotational motion of solvents, not inertial motion. Torsional motion between two anthracene rings and stretching motion of central C-C bond was observed during the reaction.
E-mail lcm1217@postech.ac.kr