Pump–probe polarization anisotropy study of doubly degenerate electronic reorientation in silicon naphthalocyanine

Abstract

Articles you may be interested inComparison of polarizable continuum model and quantum mechanics/molecular mechanics solute electronic polarization: Study of the optical and magnetic properties of diazines in water Electronic polarization spectroscopy of metal phthalocyanine chloride compounds in superfluid helium droplets Measurements with 26 fs pulses that cover the Q(0 -0) band of silicon 2,3-naphthalocyanine bis͑trihexylsilyloxide͒ yielded an initial anisotropy of 0.40 that decayed to 0.12 over 200 fs. This contradicts theories predicting anisotropy decay from 7/10 to 1/10. Including ground state bleaching and excited state absorption, anisotropy decay from 2/5 to 1/10 is predicted for degenerate electronic reorientation and dephasing.

Polarized pump-probe measurements of electronic motion via a conical intersection

“…Only the highest frequency vibration was observed in prior pump-probe data. 38 Another vibration can be inferred from the ϳ500 fs period beating of the apparent vibrational amplitude in the magic angle signal. The three lowest frequency vibrations do not appear in the magic angle signal.…”

“…38,40,51 The magic angle signal measures isotropic dynamics, while the pump-probe polarization anisotropy ͓Eq. ͑6.4͒ of Ref.…”

“…62 Experimentally, the stabilization energies are determined from the amplitude of the vibrational modulation of the signal, the pulse duration, the pulse spectrum, and the equilibrium absorption and emission spectra of the sample using standard numerical fitting procedures for determination of vibrational reorganization energies. 54,84 Since the Jahn-Teller stabilization energies are much smaller than the vibrational frequencies, a prior hypothesis of adiabatic pseudorotation, 38 in which the electrons remain on a single surface ͑mesh or solid in Fig. 1͒, is ruled out.…”

“…The Appendix describes separate experimental signatures for these two processes based on theories for the polarization anisotropy of coherently excited electronic states. [35][36][37][38][39][40][41][42] Like g and h, the separate experimental signatures of electronic dephasing and electronic population transfer depend on the electronic basis set ͑and the distinction is only physically significant once the basis set has been specified͒. However, the experimental signatures of complete electronic equilibration by means of a conical funnel, such as the g-h plane or FIG.…”

“…48 The conical intersection dynamics are slow enough to measure because the electrons involved in the electronic transition are delocalized and the naphthalocyanine ring vibrations are weakly coupled to electronic excitation. Naphthalocyanine's size makes diffusive rotation in the benzonitrile solvent slow ͑ϳ450 ps͒, 38 so that any faster changes in the polarization dependence of the signal must be attributed to electronic dynamics without molecular rotation.…”