Cooperative effect of hydrogen-bonded chains in the environment of a pi --> pi* chromophore.

Laser resonant two-photon ionization UV spectra provide clear evidence that the effect of increasing the length of the hydrogen-bonded chain consisting of molecules such as NH(3), H(2)O, or CH(3)OH on the pi --> pi* excitations of cis-7-hydroxyquinoline (cis-7HQ) is strongly cooperative [ Thut ; et al. J. Phys. Chem. A 2008 , 112 , 5566. ] A theoretical analysis of the experimental data is provided to identify the origin of this cooperativity for four chains. The computational method to determine the changes of the electronic structure of a molecule due to interactions with its environment uses the nonempirical expression for the embedding potential [ Wesolowski ; Warshel J. Phys. Chem. 1993 , 97 , 8050. ] It is concluded that the electronic coupling between the molecules at the ends of the chain, which are hydrogen-bonded to cis-7HQ, plays a crucial role in this cooperativity.