Azobenzene EZ photoisomerization, following excitation to the bright S(ππ*) state, is investigated by means of ab initio CASSCF optimizations and perturbative CASPT2 corrections. Specifically, by elucidating the S(ππ*) deactivation paths, we explain the mechanism responsible for azobenzene photoisomerization, the lower isomerization quantum yields observed for the S(ππ*) excitation than for the S1(nπ*) excitation in the isolated molecule, and the recovery of the Kasha rule observed in sterically hindered azobenzenes. We find that a doubly excited state is a photoreaction intermediate that plays a very important role in the decay of the bright S(ππ*). We show that this doubly excited state, which is immediately populated by molecules excited to S(ππ*), drives the photoisomerization along the torsion path and also induces a fast internal conversion to the S1(nπ*) at a variety of geometries, thus shaping (all the most important features of) the S(ππ*) decay pathway and photoreactivity. We reach this conclusion by determining the critical structures, the Minimum Energy Paths originating on the bright S(ππ*) state and on other relevant excited states including S1(nπ*) and by characterizing the conical intersections seams that are important in deciding the photochemical outcome. The model is consistent with the most recent time-resolved spectroscopic and photochemical data.

I. Conti, M. Garavelli, G. Orlandi (2008). The different photoisomerization efficiency of Azobenzene in the lowest nπ* and ππ* singlets: the role of a phantom state. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 130, 5216-5230 [10.1021/ja710275e].

The different photoisomerization efficiency of Azobenzene in the lowest nπ* and ππ* singlets: the role of a phantom state

CONTI, IRENE;GARAVELLI, MARCO;ORLANDI, GIORGIO
2008

Abstract

Azobenzene EZ photoisomerization, following excitation to the bright S(ππ*) state, is investigated by means of ab initio CASSCF optimizations and perturbative CASPT2 corrections. Specifically, by elucidating the S(ππ*) deactivation paths, we explain the mechanism responsible for azobenzene photoisomerization, the lower isomerization quantum yields observed for the S(ππ*) excitation than for the S1(nπ*) excitation in the isolated molecule, and the recovery of the Kasha rule observed in sterically hindered azobenzenes. We find that a doubly excited state is a photoreaction intermediate that plays a very important role in the decay of the bright S(ππ*). We show that this doubly excited state, which is immediately populated by molecules excited to S(ππ*), drives the photoisomerization along the torsion path and also induces a fast internal conversion to the S1(nπ*) at a variety of geometries, thus shaping (all the most important features of) the S(ππ*) decay pathway and photoreactivity. We reach this conclusion by determining the critical structures, the Minimum Energy Paths originating on the bright S(ππ*) state and on other relevant excited states including S1(nπ*) and by characterizing the conical intersections seams that are important in deciding the photochemical outcome. The model is consistent with the most recent time-resolved spectroscopic and photochemical data.
2008
I. Conti, M. Garavelli, G. Orlandi (2008). The different photoisomerization efficiency of Azobenzene in the lowest nπ* and ππ* singlets: the role of a phantom state. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 130, 5216-5230 [10.1021/ja710275e].
I. Conti; M. Garavelli; G. Orlandi
File in questo prodotto:
Eventuali allegati, non sono esposti

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: https://hdl.handle.net/11585/62998
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 180
  • ???jsp.display-item.citation.isi??? 174
social impact