Time-resolved electron paramagnetic resonance study of the lowest excited triplet states of trans-cinnamic acid and trans-cinnamate anion

Time-resolved and steady-state electron paramagnetic resonance spectra have been observed for the lowest excited triplet (T1) states of trans-cinnamic acid (RCOOH) and trans-cinnamate anion (RCOO−) in methanol-water and in stretched poly(vinyl alcohol) films at 77 K. The zero-field splitting parameters |D| and |E| in the T1 state slightly increase on deprotonation. The sublevel preferentially populated by intersystem crossing in Ty in RCOOH, while the in-plane Tx and Ty sublevels are prefentially populated in RCOO− (the x and y axes are close to the long and short in-plane molecular axis, respectively).