Unusual photochemical dynamics of a bridged azobenzene derivative

Abstract

In a large-scale simulation study of ultrafast photochemical dynamics for an azobenzene compound with an additional ethylenic bridge we have found unexpected features: while the dynamics starting from the Z isomer follow a barrierless path with steep gradients, the dynamics starting from the E isomer proceed through a different conical intersection surrounded by a rather flat potential energy landscape and then encounter a sizeable barrier in the electronic ground state that markedly influences the reaction behavior. Direct comparisons with experimental static UV spectra, quantum yields, and transient absorption spectra show good agreement and reveal signatures of this unusual behavior.

Nonadiabatic ab initio molecular dynamics of photoisomerization in bridged azobenzene

“…One CI was reported to play an important part in nonadiabatic transitions between the two states involved in cis-trans photodynamics processes. 19,21 As can be seen from Figure 5, nonadiabatic transitions in the dynamics starting from 1Z pass through the avoided crossing near CI 1 and CI 2 between S 1 and S 0 states.…”

“…Previous dynamics simulations [19][20][21] demonstrated that one minimum-energy CI plays an important part in nonadiabatic transitions between the two states involved in transcis photodynamics processes. However, in this work, CI 1 and CI 2 were found to be responsible for nonadiabatic transitions during 1E-1Z photoisomerization.…”

“…18 Combining an AM1 floating-occupation configuration interaction technique (FOCI-AM1) with Tully's fewest switches surface hopping method, 23 a recent dynamics simulation 19 indicated that trans-cis and cis-trans photoisomerization reactions proceed through two different minimum-energy conical intersections (CIs), with the dynamics starting from the cis isomer following a barrierless path with steep gradients and the dynamics starting from the trans isomer encountering a sizeable barrier in the ground state. In comparative studies of the trans-cis isomerizations of azobenzene and its bridged form by Jiang et al, 20 one minimum-energy CI is found to exist in both isomerization processes, and twisting of the two phenyl rings in bridged azobenzene around their N-C bonds is hindered by the presence of the bridge structure.…”

“…1,2 Nonadiabatic dynamics simulations based on several methods have been performed to reveal the photoisomerization mechanisms of bridged azobenzene. [18][19][20][21][22] Böckmann et al investigated the nonadiabatic dynamics processes of trans-cis and cis-trans photoisomerization through an ab initio molecular dynamics simulation. 18 The -CH 2 -CH 2 -bridge does not hinder photoisomerization and it suitably preorients the phenyl rings such that bridged azobenzene can more easily a) Electronic addresses: aihuagao@dicp.ac.cn, libinsnet@dicp.ac.cn, and pyzhang@dicp.ac.cn.…”

Well-Tempered Metadynamics as a Tool for Characterizing Multi-Component, Crystalline Molecular Machines

“…The problem is exacerbated by the necessary treatment of electrons in molecular machines whose motions depend on excited state transition states or the formation of chemical bonds. Nevertheless, such systems have been tackled successfully using ab initio approaches, in molecular switches, 28,29 rotaxanetype molecular shuttles 10,30 and photochemically-driven, artificial cilia. 31 Where conformational properties and the stochastic behavior of molecules are solely responsible for their function, molecular dynamics (MD) 10,20,30,[32][33][34] and molecular mechanics (MM) 31,33,[35][36][37] are more useful and can typically obtain information on processes acting faster than 100 ns.…”