UV-Light-Induced Vibrational Coherences: The Key to Understand Kasha Rule Violation in trans-Azobenzene

作者：Nenov Artur; Borrego Varillas Rocio; Oriana Aurelio; Ganzer Lucia; Segatta Francesco; Conti Irene; Segarra Marti Javier; Omachi Junko; Dapor Maurizio; Taioli Simone; Manzoni Cristian; Mukamel Shaul; Cerullo Giulio^*; Garavelli Marco^*

来源：Journal of Physical Chemistry Letters, 2018, 9(7): 1534-1541.

DOI：10.1021/acs.jpclett.8b00152

We combine sub-20 fs transient absorption spectroscopy with state-of-the-art computations to study the ultrafast photoinduced dynamics of trans-azobenzene (AB). We are able to resolve the lifetime of the pi pi* state, whose decay within ca. 50 fs is correlated to the buildup of the n pi* population and to the emergence of coherences in the dynamics, to date unobserved. Nonlinear spectroscopy simulations call for the CNN in-plane bendings as the active modes in the subps photoinduced coherent dynamics out of the pi pi* state. Radiative to kinetic energy transfer into these modes drives the system to a high-energy planar n pi*/ground state conical intersection, inaccessible upon direct excitation of the lie state, that triggers an ultrafast (0.45 ps) nonproductive decay of the n pi* state and is thus responsible for the observed Kasha rule violation in UV excited trans-AB. On the other hand, cis-AB is built only after intramolecular vibrational energy redistribution and population of the NN torsional mode.

• 出版日期2018-4-5