Excited state conformational dynamics of semiflexibly bridged electron donor-acceptor systems: a semiempirical CI-study including solvent effects

Semiempirical (AM1) molecular orbital theory with configuration interaction has been used to investigate the harpooning mechanism proposed from experimental studies on semiflexibly bridged electron donor-acceptor systems. Our calculations on the charge-transfer state of N-phenyl-4-(4-cyano-naphth-1-ylmethyl)-piperidine, 1, confirm the proposed harpooning mechanism including an intermediate loosely folded charge-transfer state and reproduce the thermodynamics obtained from our spectroscopic studies closely. The structural details of the extended (ECT), intermediate (ICT) and compact (CCT) charge-transfer states are discussed, as are the transition states connecting them. Solvent effects have been modeled using self-consistent reaction field (SCRF) calculations within the polarized continuum model. The effect of solvent polarity on the stabilities of the three charge-transfer states is discussed.