Sub-Picosecond Intersystem Crossing and Vibrational Cooling in the Triplet Manifold of 1-NITRONAPHTHALENE

Details Sub-Picosecond Intersystem Crossing and Vibrational Cooling in the Triplet Manifold of 1-NITRONAPHTHALENE Sub-Picosecond Intersystem Crossing and Vibrational Cooling in the Triplet Manifold of 1-NITRONAPHTHALENE

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009mss..confemf12r&link_type=abstract

"International Symposium On Molecular Spectroscopy, 64th Meeting, Held 22-26 June, 2009 at Ohio State University. http://molspec

Physics

Dynamics

Scientific paper

The electronic energy relaxation of 1-nitronaphthalene (1NN) was studied in different solvents using broadband transient absorption spectroscopy with femtosecond time resolution. UV excitation of 1NN populates an unrelaxed S_1(ππ*) state, which decays by conformational relaxation (primarily twisting of the NO_2 group) with a time constant of 100 fs. The twisting of the NO_2 group and formation of a structurally relaxed singlet state opens up a doorway for ultrafast intersystem crossing (ISC) to a high-energy receiver triplet state T_n(nπ*), which then undergoes internal conversion to form a vibrationally excited T_1(π π*) state. Quantum chemical calculations that include solvent effects support the experimental observations. Our results show that an essentially barrierless path connects the initial S_1 state to the receiver T_n state, which enables the observation of vibrational energy transfer and its dependence on the surrounding solvent. According to this kinetic model, which was first proposed by Crespo-Hernández et al. for 1-nitropyrene[1], the S_1(π π) electronic energy decays rapidly and irreversibly to dark triplet states, explaining why small nitro-polycyclic aromatic compounds are typically considered to be nonfluorescent.
[1] C. E. Crespo-Hernández, G. Burdzinski, R. Arce, J. Phys. Chem. A., 2008, 112,6313

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