On the origin of ultrafast nonradiative transitions in nitro-polycyclic aromatic hydrocarbons: Excited-state dynamics in 1-nitronaphthalene

Journal Article · Mon Dec 14 00:00:00 EST 2009 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3272536· OSTI ID:21559820

Reichardt, Christian; Vogt, R Aaron; Crespo-Hernandez, Carlos E ^[1]

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1. Department of Chemistry, Center for Chemical Dynamics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106 (United States)

The electronic energy relaxation of 1-nitronaphthalene was studied in nonpolar, aprotic, and protic solvents in the time window from femtoseconds to microseconds. Excitation at 340 or 360 nm populates the Franck-Condon S{sub 1}({pi}{pi}{sup *}) state, which is proposed to bifurcate into two essentially barrierless nonradiative decay channels with sub-200 fs lifetimes. The first main decay channel connects the S{sub 1} state with a receiver T{sub n} state that has considerable n{pi}{sup *} character. The receiver T{sub n} state undergoes internal conversion to populate the vibrationally excited T{sub 1}({pi}{pi}{sup *}) state in 2-4 ps. It is shown that vibrational cooling dynamics in the T{sub 1} state depends on the solvent used, with average lifetimes in the range from 6 to 12 ps. Furthermore, solvation dynamics competes effectively with vibrational cooling in the triplet manifold in primary alcohols. The relaxed T{sub 1} state undergoes intersystem crossing back to the ground state within a few microseconds in N{sub 2}-saturated solutions in all the solvents studied. The second minor channel involves conformational relaxation of the bright S{sub 1} state (primarily rotation of the NO{sub 2}-group) to populate a dissociative singlet state with significant charge-transfer character and negligible oscillator strength. This dissociative channel is proposed to be responsible for the observed photochemistry in 1-nitronaphthalene. Ground- and excited-state calculations at the density functional level of theory that include bulk and explicit solvent effects lend support to the proposed mechanism where the fluorescent S{sub 1} state decays rapidly and irreversibly to dark excited states. A four-state kinetic model is proposed that satisfactorily explains the origin of the nonradiative electronic relaxation pathways in 1-nitronaphthalene.

• OSTI ID: 21559820
• Journal Information: Journal of Chemical Physics, Vol. 131, Issue 22; Other Information: DOI: 10.1063/1.3272536; (c) 2009 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALCOHOLS
CHARGE EXCHANGE
DENSITY FUNCTIONAL METHOD
DISSOCIATION
EXCITATION
FLUORESCENCE
INTERNAL CONVERSION
LIFETIME
NITROGEN DIOXIDE
OSCILLATOR STRENGTHS
PHOTOCHEMISTRY
POLYCYCLIC AROMATIC HYDROCARBONS
REACTION KINETICS
RELAXATION
SOLUTIONS
SOLVATION
SOLVENTS
VIBRATIONAL STATES
AROMATICS
CALCULATION METHODS
CHALCOGENIDES
CHEMISTRY
CONVERSION
DECAY
DISPERSIONS
EMISSION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITED STATES
HOMOGENEOUS MIXTURES
HYDROCARBONS
HYDROXY COMPOUNDS
KINETICS
LUMINESCENCE
MIXTURES
NITROGEN COMPOUNDS
NITROGEN OXIDES
NUCLEAR DECAY
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTON EMISSION
VARIATIONAL METHODS