A theoretical study on the factors influencing cyanine photo isomerization: The case of thiacyanine in gas phase and in methanol

作者：Improta R; Santoro F^*

来源：Journal of Chemical Theory and Computation, 2005, 1(2): 215-229.

DOI：10.1021/ct049899r

The effects influencing cyanine photoisomerization on the S(1) surface in the condensed phase have been investigated by an integrated quantum mechanical approach, focused mainly on 3,3'-diEt-2,2'-thiacyanine. After excitation, a barrierless motion, involving the torsion coupled to bond skeletal deformation, leads to a slightly nonplanar local C(2) minimum, which we propose to be the fluorescent state. Crossed a barrier of approximate to 120 cm-(1), a steeper path drives to a more stable C(1) minimum S(1)-Min,corresponding to a pseudoperpendicular twisted intramolecular charge transfer (TICT) state. CAS(6,6) optimization allows for locating the lowest energy S(1)/S(0) conical intersection in the isomerization path which is reached from S(1)-Min by an increased asymmetry of the two rings and a marked pyramidalization at one N center. The S1 surface is rather flat in the Franck-Condon region and suggests that other paths can be competitive with the minimum energy one. The comparison among different cyanines shows how variation of the molecular scaffold and/or of its substituents modulate the dynamics of the photoisomerization. All the indications coming from our computations are in line with and provide an explanation to the available experimental results.

• 出版日期2005-4