Photochromic Mechanism of a Bridged Diarylethene: Combined Electronic Structure Calculations and Nonadiabatic Dynamics Simulations

Abstract

Intramolecularly bridged diarylethenes exhibit improved photocyclization quantum yields because the anti-syn isomerization that originally suppresses photocyclization in classical diarylethenes is blocked. Experimentally, three possible channels have been proposed to interpret experimental observation, but many details of photochromic mechanism remain ambiguous. In this work we have employed a series of electronic structure methods (OM2/MRCI, DFT, TDDFT, RI-CC2, DFT/MRCI, and CASPT2) to comprehensively study excited state properties, photocyclization, and photoreversion dynamics of 1,2-dicyano[2,2]metacyclophan-1-ene. On the basis of optimized stationary points and minimum-energy conical intersections, we have refined experimentally proposed photochromic mechanism. Only an S/S minimum-energy conical intersection is located; thus, we can exclude the third channel experimentally proposed. In addition, we find that both photocyclization and photoreversion processes use the same S/S conical intersection to decay the S system to the S state, so we can unify the remaining two channels into one. These new insights are verified by our OM2/MRCI nonadiabatic dynamics simulations. The S excited-state lifetimes of photocyclization and photoreversion are estimated to be 349 and 453 fs, respectively, which are close to experimentally measured values: 240 ± 60 and 250 fs in acetonitrile solution. The present study not only interprets experimental observations and refines previously proposed mechanism but also provides new physical insights that are valuable for future experiments.

“On-The-Fly” Non-Adiabatic Dynamics Simulations on Photoinduced Ring-Closing Reaction of a Nucleoside-Based Diarylethene Photoswitch

“…Trajectory-based semi-classical non-adiabatic dynamics simulations approaches with different schemes were extensively employed to simulate a series of ultrafast excited-state relaxation processes in chemical and biological systems, and materials [ 87 , 95 , 96 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 ]. In the present work, trajectory-based surface hopping dynamics simulations involving the lowest two singlet states were carried out with the recently developed method proposed by Zhu et al [ 127 ].…”

“…Despite many theoretical investigations having been performed before to explore the photochromic properties of diarylethenes, most of them are concentrated on the ground state structures as well as relevant absorption spectroscopic properties [ 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. In contrast, few theoretical works concerning the microscopic details of the photochromic mechanism of diarylethenes have been conducted [ 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 ]. Such researches on the photochromic mechanisms of diarylethenes can be traced back to the beginning of the 21st century.…”

“…Recently, our group also employed static electronic structure calculations (DFT/MRCI, RI-CC2, TDDFT, CASPT2//CASSCF, etc.) in combination with a semi-empirical method (OM2/MRCI) based on non-adiabatic dynamics simulations to explore the photochromic mechanism of bridged diarylethenes, based on which the experimentally proposed photochromic mechanism is refined [ 40 , 87 ].…”

Unraveling ultrafast dynamics of the photoswitchable bridged dithienylethenes under structural constraints

“…By referring to previous work, this characteristic time is unambiguously attributed to the ultrafast photocyclization via the S1 FC state. 16,31 Besides photocyclization, there is the parallel relaxation of the AP conformer from the FC region to the relaxed excited singlet state noticed S 2 IJK AP . It is worth to note that τ1 is always higher compared to the unbridged analog which suggests that the polyether chain pulls apart the reactive carbons.…”

“…By this way, we have reported in 2010 two photocyclization pathways for cyano-substituted DAEs, 14 results confirmed recently by advanced ab-initio calculations. 16 Similarly, the ultrafast excited state and reaction dynamics of a series of inverse bridged DTEs have been fully understood in solution 17 and in the gas-phase. 15a In particular, we were able to prove that the systems photocyclized directly from the Franck-Condon region (∼120 fs) and not from the first relaxed excited state.…”