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 ππ∗ state, whose decay within ca. 50 fs is correlated to the buildup of the nπ∗ 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 ππ∗ state. Radiative to kinetic energy transfer into these modes drives the system to a high-energy planar nπ∗/ground state conical intersection, inaccessible upon direct excitation of the nπ∗ state, that triggers an ultrafast (0.45 ps) nonproductive decay of the nπ∗ 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.

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

Borrego-Varillas R.;Oriana A.;Ganzer L.;Manzoni C.;Cerullo G.;
2018

Abstract

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 ππ∗ state, whose decay within ca. 50 fs is correlated to the buildup of the nπ∗ 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 ππ∗ state. Radiative to kinetic energy transfer into these modes drives the system to a high-energy planar nπ∗/ground state conical intersection, inaccessible upon direct excitation of the nπ∗ state, that triggers an ultrafast (0.45 ps) nonproductive decay of the nπ∗ 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.
File in questo prodotto:
File Dimensione Formato  
jpclett_azo_2018.pdf

Accesso riservato

: Publisher’s version
Dimensione 3.96 MB
Formato Adobe PDF
3.96 MB Adobe PDF   Visualizza/Apri
11311-1123071_Cerullo.pdf

accesso aperto

: Post-Print (DRAFT o Author’s Accepted Manuscript-AAM)
Dimensione 2.39 MB
Formato Adobe PDF
2.39 MB Adobe PDF Visualizza/Apri

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11311/1123071
Citazioni
  • ???jsp.display-item.citation.pmc??? 18
  • Scopus 74
  • ???jsp.display-item.citation.isi??? 72
social impact