GIANT-DIPOLE MOMENT IN A TRIAD SYSTEM - MECHANISMS OF ANISOTROPIC PHOTORESPONSE IN THE TRANSIENT DC CONDUCTIVITY OF DIPOLAR SOLUTES

A transient de conductivity method was used to observe formation of a giant dipole moment for the triad molecule MA-ANI-NI thalimide-dimethy lphenyl-naphthalenediimide-octyl) in toluene. The independence of the dipole moment on excitation wavelength indicates high efficiency of in tramolecular energy or (and) electron transfer. The effect of light po larization on the DC conductivity signal caused by a photoinduced incr ease in solute dipole moment is considered in detail. It is shown that the time variation of the signal includes information about structura l anomalies in the angular distribution function of molecular dipoles and depends on light polarization even for zero ground state dipole mo ment. Nonzero ground state dipole moment and (or) electric field depen dence of the charge transfer rate constants give an additional source for an anisotropic photoresponse signal. Analysis of the photoresponse and its anisotropy for the triad gives ground (mu g), first (mu(1)), and second (mu(2)) excited state dipole moments as follows: mu(g) = 12 +/- 5 D, mu(1) = 35 +/- 10, and mu(2) = 87 +/- 6 D. The lifetime of t he giant dipole state is tau = 290 +/- 10 ns, and the molecule's rotat ional time is tau(r) = 1.6 +/- 0.15 ns.