An ab initio study on the photoisomerization in 2-styrylpyridine

Abstract

We report results of a theoretical study on photoinduced processes in 2-styrylpyridine. The geometries and the relative energies of the possible conformers were investigated using the second-order Møller–Plesset (MP2) and algebraic diagrammatic construction to second-order (ADC(2)) methods and the cc-pVTZ basis set. The complete active space self consistent field (CASSCF) method is used for locating the minimum-energy conical intersection (MECI) geometries between the S₀ and S₁ states. In addition to the twisted-pyramidalized MECI points along the trans and cis isomerization pathways, S₁/S₀ cooperating-ring MECI and cyclized-ring MECI structures, lying on the cyclization pathways of cis-2-styrylpyridine, were also located. Except the twisted pyramidalized CI2 and cyclized Cyc-CI3, all the other MECI points are found to be accessible from either one or more Franck–Condon points. The possibilities for the cis−trans isomerization and cyclization processes are discussed along the image-dependent pair potential (IDPP) paths.