Theoretical Study On Photochemical Ring-opening Reaction Of 2,2-diphenyl (2H) Chromene By Nonadiabatic Molecular Dynamics

In this paper,the photochemical ring-opening reaction of 2,2-diphenyl（2H）chromene（DPC）was investigated by static electronic structure calculation and trajectory surface hopping molecular dynamics simulation method.This thesis consists of three parts:the first part summarizes the research progress of 2,2-diphenyl（2H）chromene（DPC）photochemical ring-opening reaction and the calculation method used;the second part reports the electronic structure of 2,2-diphenyl（2H）chromene（DPC）photochemical ring-opening reaction mechanism;The third part introduces trajectory surface hopping molecular dynamics simulation of 2,2-diphenyl（2H）chromene（DPC）for analyzing statistical data and microdynamic properties,including optical reaction quantum yield,excited state lifetime,channel branching ratio,etc.Chapter 1 briefly introduces the discoloration mechanism of photochromic materials,the development of various materials and its potential practical application.In addition,the research status of benzopyran derivatives and the mechanism of photoinduced ring-opening and isomerization are briefly introduced.At the end of the first chapter,we briefly introduce the theoretical computational methods employed in this paper.The second chapter describes the theoretical study of the photoinduced ring-opening reaction mechanism of DPC based on time-dependent density functional theory（TDDFT）at the level of B3LYP/6-31G（d）.For this reaction process,we obtained a series of key reaction stationary points through geometry optimizations.The study found that DPC has two stable formations with axial chirality symmetry,named DPC-C and DPC-T,respectively,of which DPC-T is more stable and has a weight of about 82%at room temperature.For these two chiral isomers,we optimized three conical intersections（CI-S₃/S₂-C（T）,CI-S₂/S₁-C（T）,CI-S₁/S₀-C（T））on their photoreaction paths,respectively.For DPC-C（or DPC-T）,the possible photoreaction mechanism is as follows:When excited to S₂ state,the molecule realizes ring-opening and isomerization process along S₂-FC-C（T）→CI-S₃/S₂-C（T）→S₂-CF-C（T）→CI-S₂/S₁-C（T）→CI-S₁/S₀-C（T）→S₀-OF-C（T）→S₀-OF-tc-C（T）→S₀-OF-tt-C（T）;the main reaction path with respect to S₁ excitation is S₁-FC-C（T）→CI-S₁/S₀-C（T）→S₀-OF-C（T）→S₀-OF-tc-C（T）→S₀-OF-tt-C（T）.It should be noted that not all molecules will generate ring-opening products after the decay on excited states,and a petty part of the products are ring-closed reactants.Furthermore,the benzopyran rings around the CI-S₂/S₁-C,CI-S₂/S₁-T and CI-S₁/S₀-C are in a near-planar geometries,Whether it is DPC-C or DPC-T,Chiral ring-opening products may be generated after S₁ excitation.In Chapter 3,we use CAM-B3LYP-D3/DEF2-SVP levels to conduct non-adiabatic molecular dynamics simulations to study the photochemical open-loop reaction dynamics of DPC after S₁excitation.We simulated a total of 300 trajectories with initially on S₁ excited state,of which200 trajectories are T-isomers and 100 trajectories are C-isomers.Analysis of the results of molecular dynamics simulations revealed that the average lifetime of S₁ excited states in DPC molecules is 254.74 fs,with a total quantum yield ofφ_CF→OF-tc=0.847,which is generally consistent with the experimental results.Through the analysis of the trajectories,we obtained that the average lifetimes of ring-opening and isomerism corresponding to the C configuration were 477.96 fs and 1031.26 fs,and the ring-opening yield was 73.0%,of which 49 trajectories experienced chiral isomerism;The corresponding ring-opening and isomerization lifetimes for the T configuration were 143.13 fs and 1122.55 fs,and the ring-opening yield was 90.5%,with30 trajectories undergoing chiral isomerization.The above research results have a good theoretical reference value for the subsequent design and synthesis of spiro-ring photochromic materials.