Temperature dependence of the emission spectra of o-, p- and m-fluorobenzaldehyde in the vapor phase: rotational isomers of o- and m-derivatives

Emission and excitation spectra of o-, p- and m-fluorobenzaldehyde (o-, p- and m-FB, respectively) vapors have been measured at different temperatures and compared to one another. Temperature dependence of the phosphorescence spectrum of m-FB provides the energy difference of 70G20 cmK1 for the two rotational isomers in the T1 state and 36G20 cmK1 for those in the ground state. It is inferred from semi-empirical SCF-MO calculations and vibrational analysis of the emission spectra that the lower-lying phosphorescence origin at 24,950 cmK1 of m-FB is originating from the anti rotamer, and that the observed emission of o-FB originates from the anti rotamer. The S1–T1 energy separations of o-, p- and m-FB vapors obtained from the temperature dependence of the emission spectrum all agreed well with those obtained spectroscopically. q 2004 Elsevier B.V. All rights reserved.