Abstract
A realistic semiclassical dynamics simulation study is reported for the photoinduced ring-opening reaction of spiropyran. The main simulation results show that one pathway involves hydrogen out-of-plane (HOOP) torsion of phenyl ring nearby N atom in 254 fs on the excited state and the isomerization from cis- to trans-SP that is complete in about 10 ps on the ground state after the electron transitionπσ*; the other dominate pathway corresponds to the ring-opening reaction of trans-SP to form the most stable merocyanine (MC) product. Unlike the previous theoretical finding, one C−C bond cleavage on the real molecule rather than the C−N dissociation of the model one is more probable than the ring-opening reaction after the photoexcitation of SP. The simulation findings provide more important complementarity for interpreting experimental observations, confirming the previously theoretical studies of photochromic ring-opening process and even supplying other possible reaction mechanisms.
Highlights
The photochromic reactions of SP have been widely studied by time resolved spectroscopy to find the complex mechanism [22,23,24,25,26,27,28]
Very recent experiments show that the ring-opening reaction of unsubstituted SP (1,3,3-trimethylspiro [2H-1-benzopyran2,2-indoline], known as BIPS) [29] and double NO2substituted derivative (6,8-dinitro-BIPS) [8] involve only singlet states, while a triple state makes a contribution to the dynamic of NO2-substituted SP (6-nitro-BIPS) [23]
In comparison with the pathways in the above sections, it can be found the ionization and isomerization of excited SP with the same lifetime 254 fs are both more ultrafast than the ring-opening reaction with lifetime 422 fs, which confirm the previous conclusion that the quantum yield of MC products of this photochromic reaction is relatively less, since the internal conversion from the excited state to the ground state of SP is even more efficient [24, 28]
Summary
Spiropyran (SP) is one of the very recent most studied photochromic molecules, which are popular materials in sunglasses, optical switching, optical data storage, nonlinear optical devices, optical nanoparticles, photonic crystal, and so on [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. The most impressive features of the nuclear motions of the excited molecule are the evident C1–C2 bond stretching, twist of α, and HOOP torsion of the phenyl ring connected with N atom presented by the dihedral angle H26–C11–C8–C10 (labeled as θ).
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