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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quantum Chemical Determination of the Equilibrium Geometries and Harmonic Vibrational Frequencies of 1,1'-, 1,2'- and 2,2'-Binaphthyl in Their Ground and Excited (~1L_a) Electronic States
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Quantum Chemical Determination of the Equilibrium Geometries and Harmonic Vibrational Frequencies of 1,1'-, 1,2'- and 2,2'-Binaphthyl in Their Ground and Excited (~1L_a) Electronic States

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This work is concerned with the characterization of the lowest electronic excited states of 1,1'-, 1,2'- and 2,2'-binaphthyl, in particular with the determination of their equilibrium geometries, low-frequency vibrations, and torsional potentials, via ab initio and density functional (DFT) calculations. The methods employed are configuration interaction with singles (CIS) and time-dependent DFT, in conjunction with Hartree-Fock and DFT(B3LYP) theories for the ground states, using the 3-21G basis set. The strengths and weaknesses in these methods for these large systems were tested extensively by reference to higher level calculations performed on the benzene/biphenyl systems and on naphthalene itself. In the case of 1,2'- and 2,2'-binaphthyl the theoretical predictions are consistent with a reassignment of the experimentally observed spectrum as S_3(~1L_a)←S_0 rather than S_1(~1L_b)←S_0 as previously assumed. With this reassignment it is possible to provide definitive assignment of a number of the observed low-frequency torsional and out-of-plane bending modes, as well as a more confident identification of the conformation of the observed excited states. For 1,1'-binaphthyl the theoretical results are, however, at variance with the prevailing interpretation of the spectral data. As expected on the basis of qualitative π molecular orbital theory, π-delocalization has been found to be considerably more important in the ~1L_a excited states of the binaphthyls than in the ground and ~1L_b excited states. The different degrees of π delocalization in the ground and excited states of these biaryls provide an explanation as to why all these systems adopt nonplanar twisted geometries in their ground and ~1L_b excited states, while in their ~1L_a excited states they are computed to be either completely planar or considerably more so than in the ground state.

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