双光子协同光化学周环反应规则及其与单光子周环反应的Woodward-Hoffman规则的区别

two-photon (with frequency v) reaction (TPR) is compared with its corresponding one-photon (with frequency 2v) counterpart (OPR) both experimentally and theoretically. TPR often yields different products from its OPR, suggesting Woodward-Hoffman Rules do not apply for TPR. To explain the difference, it is proposed that Hudson-Kohler state of polyenes (HKSP), rather than the state in Huckel molecular orbital theory, acts as the lowest-lying excited state for the two-photon absorption (TPA) involved in TPR. The selection rules for pericyclic TPR are derived based on the symmetry of HKSP and frontier orbital theory.