Charge redistribution on electronic excitation. Dipole moments of cis- and trans-3-aminophenol in their S(0) and S(1) electronic states.

Rotationally resolved electronic spectroscopy in the gas phase, in the absence and presence of an applied electric field, has been used to distinguish the two conformers of 3-aminophenol (3AP) on the basis of differences in their electric dipole moments. cis-3AP has micro = 2.3 D, and trans-3AP has micro = 0.7 D, in their ground electronic states. The two observed values are approximately equal to those expected on the basis of bond dipole additivity rules. However, these rules fail to predict the large change in both the magnitude and the orientation of micro when the two conformers of 3AP absorb light. cis-3AP has micro = 3.3 D, and trans-3AP has micro = 1.7 D, in their excited S(1) electronic states; the angles of orientation of micro with respect to the a inertial axis change by 13 degrees and 38 degrees, respectively. This effect is attributed to (1)L(b)/(1)L(a) state mixing in the S(1) state.