| Abstract: | Phenol blue is a merocyanine dye that may exist in resonance between two extreme forms, a neutral keto form and a zwitterionic, charge‐separated eno form. The keto form is stable in the gas phase, while the eno form can be stabilized by solvents. In this work, the bond‐length alternation is used to monitor the change of the dipole hyperpolarizability of phenol blue continuously from the extreme eno to the other extreme keto forms. Intermediate structures were found to give the largest value for the first dipole hyperpolarizability. These values are compatible with the experimental results in different solvents and suggest that phenol blue undergoes structural changes in polar solvents. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/qua.10120 |
