title: Broadband transient absorption spectroscopy with 1- and 2-photon excitations: Relaxation paths and cross sections of a triphenylamine dye in solution.
abstract: 1-photon (382 nm) and 2-photon (752 nm) excitations to the S1 state are applied to record and compare transient absorption spectra of a push-pull triphenylamine (TrP) dye in solution. After 1-photon excitation, ultrafast vibrational and structural molecular relaxations are detected on a 0.1 ps time scale in nonpolar hexane, while in polar acetonitrile, the spectral evolution is dominated by dipolar solvation. Upon 2-photon excitation, transient spectra in hexane reveal an unexpected growth of stimulated emission (SE) and excited-state absorption (ESA) bands. The behavior is explained by strong population transfer S1 → Sn due to resonant absorption of a third pump photon. Subsequent Sn → S1 internal conversion (with τ1 = 1 ps) prepares a very hot S1 state which cools down with τ2 = 13 ps. The pump pulse energy dependence proves the 2-photon origin of the bleach signal. At the same time, SE and ESA are strongly affected by higher-order pump absorptions that should be taken into account in nonlinear fluorescence applications. The 2-photon excitation cross sections σ(2) = 32 ⋅ 10(-50) cm(4) s at 752 nm are evaluated from the bleach signal.
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-St. 2, 12489 Berlin, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Moreno
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-St. 2, 12489 Berlin, Germany.
authors.forename: A L
authors.initials: AL
authors.lastname: Dobryakov
authors.affiliation: Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia.
authors.forename: I N
authors.initials: IN
authors.lastname: Ioffe
authors.affiliation: Firefly Project, 117593 Moscow, Russia.
authors.forename: A A
authors.initials: AA
authors.lastname: Granovsky
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-St. 2, 12489 Berlin, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Hecht
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-St. 2, 12489 Berlin, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Kovalenko