Jw. Ribblett et al., Styrene and phenylacetylene: Electronic effects of conjugating substituents "off'' and "on'' the axis of a benzene ring, J CHEM PHYS, 111(18), 1999, pp. 8454-8461
Rotationally resolved fluorescence excitation spectra of several vibronic b
ands in the S-1 <-- S-0 electronic transitions of styrene (STY) and phenyla
cetylene (PA) have been obtained. Confirming earlier low resolution results
, we find that the origin band of PA is a b-type band but that the correspo
nding band of STY is an a-type band, showing that the S-1 state of PA is L-
1(b) in character (like that of most other monosubstituted benzenes! but th
at the corresponding state of STY is L-1(a). The observed changes in the ro
tational constants of PA and STY that occur when the photon is absorbed are
consistent with these assignments. Reversal in the electronic character of
the S-1 state in STY is attributed to the presence of the "off-axis'' conj
ugating - CH=CH2 group, a suggestion that is supported by the observed pola
rizations of higher vibronic bands in both molecules. (C) 1999 American Ins
titute of Physics. [S0021-9606(99)00240-8].