title: Transient IR Spectroscopic Observation of Singlet and Triplet States of 2-Nitrofluorene: Revisiting the Photophysics of Nitroaromatics.
abstract: The dynamics of 2-nitrofluorene (2-NF) in deuterated acetonitrile is studied using UV pump, IR probe femtosecond transient absorption spectroscopy. Upon excitation to the vibrationally excited S1 state, the excited-state population of 2-NF branches into two different relaxation pathways. One route leads to intersystem crossing (ISC) to the triplet manifold within a few hundred femtoseconds and the other to internal conversion (IC) to the ground state. The experiments indicate that after relaxation to the energetic minimum on S1, 2-NF undergoes internal conversion to the ground state in about 15 ps. IC within the triplet manifold is also observed as the initially populated triplet state relaxes to T1 in about 6 ps. Rotational anisotropy measurements corroborate the assignment of the transient IR frequencies and indicate a rotational diffusion time of 2-NF in the solvent of about 14 ps. The combined set of results provides a unified picture of the dynamics in photoexcited 2-NF. This to our knowledge is the first example using femtosecond vibrational spectroscopy for the study of the fundamental photoinduced processes in nitroaromatic compounds.
authors.affiliation: Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Martin A B
authors.initials: MA
authors.lastname: Larsen
authors.affiliation: Department of Chemistry, Aarhus University , Langelandsgade 140, DK-8000 Aarhus C, Denmark.
authors.forename: Jan
authors.initials: J
authors.lastname: Thøgersen
authors.affiliation: Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Anne B
authors.initials: AB
authors.lastname: Stephansen
authors.affiliation: Instituto de Química, Universidad Nacional Autónoma de México , Circuito Exterior, Ciudad Universitaria 04510, D.F. México.
authors.forename: Jorge
authors.initials: J
authors.lastname: Peon
authors.affiliation: Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Theis I
authors.initials: TI
authors.lastname: Sølling
authors.affiliation: Department of Chemistry, Aarhus University , Langelandsgade 140, DK-8000 Aarhus C, Denmark.
authors.forename: Søren R
authors.initials: SR
authors.lastname: Keiding