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Comparative Studies of the trans-cis Photoisomerizations of Azobenzene and a Bridged Chen-Wei Jiang,,

Summary: Comparative Studies of the trans-cis Photoisomerizations of Azobenzene and a Bridged
Chen-Wei Jiang,,
Rui-Hua Xie,,
Fu-Li Li,
and Roland E. Allen*,
Ministry of Education (MOE) Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed
Matter, and Department of Applied Physics, Xi'an Jiaotong UniVersity, Xi'an 710049, China, Department of
Physics, Texas A&M UniVersity, College Station, Texas 77843, United States, and Department of Physics,
Hubei UniVersity, Wuhan 430062, China
ReceiVed: August 23, 2010; ReVised Manuscript ReceiVed: December 2, 2010
Using density-functional-based molecular dynamics simulations, we have performed comparative studies of
the trans-cis isomerizations of azobenzene and bridged azobenzene (B-Ab) 5,6-dihydrodibenzo[c,g]-
[1,2]diazocine induced by n* electronic excitation. The quantum yields found in our calculations, 45% for
the bridged azobenzene versus 25% for azobenzene, are consistent with the experiment. Both isomerization
processes involve two steps: (1) Starting from the trans structure, each molecule moves on its S1 excited-
state potential energy surface, via rotation around the NN bond, to an avoided crossing near the S1/S0 conical
intersection, where de-excitation occurs. (2) Subsequently, in the electronic ground state, there is further
rotation around the NN bond, accompanied by twisting of the phenyl rings around their CN bonds, until the
cis geometry is achieved. Because of its lower symmetry and smaller initial CNNC dihedral angle, the bridged


Source: Allen, Roland E. - Department of Physics and Astronomy, Texas A&M University


Collections: Physics