title: Effect of ring torsion on intramolecular vibrational redistribution dynamics of 1,1'-binaphthyl and 2,2'-binaphthyl.
abstract: The role of ring torsion in the enhancement of intramolecular vibrational energy redistribution (IVR) in aromatic molecules was investigated by conducting excitation and dispersed fluorescence spectroscopy of 1,1'-binaphthyl (1,1'-BN) and 2,2'-BN. The dispersed fluorescence spectra of 1,1'-BN in the origin region of S(1)-S(0) were well resolved, which presented 25-27 cm(-1) gaps of torsional mode in the ground state. The overall profile of the dispersed spectra of 1,1'-BN is similar to that of naphthalene. In contrast, the spectra of 2,2'-BN were not resolved due to the multitude of the active torsional modes. In both cases, dissipative IVR was observed to take place with a relatively small excess vibrational energy: 237.5 cm(-1) for 1,1'-BN and 658 cm(-1) for 2,2'-BN, which clearly shows that ring torsion efficiently enhances the IVR rate. Ab initio and density functional theory calculations with medium-sized basis sets showed that the torsional potential of 1,1'-BN has a very flat minimum over the range of torsional angles from ca. 60° to 120°, whereas that of 2,2'-BN showed two well-defined potential minima at ca. 40° and 140°, in resemblance to the case of biphenyl. In this work, we propose that aromatic molecules be classified into "strong" and "weak" torsional hindrance cases: molecules with strong hindrance case show shorter torsional progressions and more effective IVR dynamics than do those with weak hindrance.
authors: Department of Physics and School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Pohang, Korea. nklee@postech.ac.kr
authors: Nam Ki
authors: NK
authors: Lee
authors: Soonyong
authors: S
authors: Park
authors: Myung-Han
authors: MH
authors: Yoon
authors: Zee Hwan
authors: ZH
authors: Kim
authors: Seong Keun
authors: SK
authors: Kim
mesh_terms: D009281:Naphthalenes / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics; D014732:Vibration
chemical_list: D009281:Naphthalenes; C031721:naphthalene; C412331:2,2'-binaphthyl; C412330:1,1'-binaphthyl