  Herein we studied the excited state dynamics of two bis-amino substituted
anthraquinone (AQ) derivatives. Femtosecond transient absorption spectra show
that intersystem crossing (ISC) takes place in 190-320 ps, and nanosecond
transient absorption spectra demonstrated unusually short triplet state
lifetime (2.1-5.4 us) for the two AQ derivatives at room temperature. Pulsed
laser excited time-resolved electron paramagnetic resonance (TREPR) spectra
shows an inversion of the electron spin polarization (ESP) phase pattern of the
triplet state at longer delay time. Spectral simulations show that the faster
decay of the Ty sublevel (x = 15.0 us, y = 1.50 us, z = 15.0 us) rationalizes
the short T1 state lifetime and the ESP inversion. Computations taking into
account the electron-vibrational coupling, i.e., the Herzberg-Teller effect,
successfully rationalize the TREPR experimental observations.
