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  • American Institute of Physics (AIP)  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Fluorescence excitation spectra of the S1 states of isolated trienes (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2412-2415 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: First observation of fluorescence for simple, linear trienes is reported. S1←S0 fluorescence excitation spectra of hexatriene and octatriene indicate large differences between the S0 and S1 potential energy surfaces. Activation energy of 〈200 cm−1 for the S1 state nonradiative decay is tentatively ascribed to isomerization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462040
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  • 2
    Electronic Resource
    Electronic Resource
    Spectroscopic and dynamical studies of the S1 and S2 states of decatetraene in supersonic molecular beams (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 4739-4750 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence and fluorescence excitation spectra of all-trans-2,4,6,8-decatetraene have been obtained in free jets and in inert-gas clusters. In isolated decatetraene, excitation into 1 1Bu (S2) results in emission from both S2 (1 1Bu→1 1Ag) and S1 (2 1Ag→1 1Ag) on time scales that are faster than the 10 ns experimental resolution. In clusters, rapid electronic and vibrational relaxation leads to long-lived (360 ns) emission from thermally relaxed levels of S1. Direct excitation of low-lying, S1 vibronic levels in cold, isolated molecules also results in long-lived S1→S0 fluorescence, as expected for this symmetry-forbidden transition. The detection of S1 emission in free decatetraene has permitted the first detailed study of the vibronic structure and kinetics of the 2 1Ag state of an isolated, all-trans linear polyene. The S1←S0 fluorescence excitation spectrum is rich in low-frequency vibronic progressions. Analysis of this spectrum suggests that the transition not only is made allowed by vibronic coupling involving low-frequency bu skeletal modes (Herzberg–Teller coupling), as for polyenes in condensed phases, but also gains intensity from interactions between the electronic motion and the hindered rotations (torsions) of the terminal methyl groups. Preliminary analysis suggests that the barriers to internal rotation of the methyl groups must be substantially reduced in the 2 1Ag (S1) state. For isolated decatetraene, the 2 1Ag fluorescence lifetimes show a monotonic decrease with increasing vibrational energy, presumably due to increased mixing with the 1 1Bu state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461749
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  • 3
    Electronic Resource
    Electronic Resource
    The 2 1Ag state of trans,trans-1,3,5,7-octatetraene in free jet expansions (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3777-3794 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One- and two-photon fluorescence excitation and emission spectra of the S1↔S0 transition of trans,trans-1,3,5,7-octatetraene have been measured for the first time in free jet expansions. The one-photon excitation spectrum is the same, with the exception of significant differences in the intensities of a few lines, as the two-color, resonance-enhanced, two-photon ionization spectrum, previously assigned to the 2 1A'←1 1A' transition of cis,trans-1,3,5,7-octatetraene. However, comparison of the one- and two-photon fluorescence excitation spectra shows clearly that the carrier of the spectrum has inversion symmetry, as expected for trans,trans-1,3,5,7-octatetraene. The one-photon spectrum is built on bu Herzberg–Teller promoting modes, which are origins of progressions in ag modes, while the two-photon spectrum is due to a single progression in ag modes starting from the 2 1Ag←1 1Ag electronic origin. The appearance of out-of-plane vibrations, possibly including torsions of the polyene framework, suggests large differences in force constants and perhaps in the geometries of the 2 1Ag and 1 1Ag potential surfaces. For 2 1Ag vibronic levels with energies ≤1000 cm−1, the fluorescence lifetimes vary between 170 and 450 ns due to the dependence of radiative and nonradiative decay rates on the vibronic state. An abrupt increase in the nonradiative decay rates at ∼2100 cm−1 excess energy is tentatively ascribed to trans→cis isomerization. This work demonstrates that the one- and two-photon cross sections of the 2 1Ag←1 1Ag transitions of all-trans linear polyenes are sufficiently large to allow the study of 2 1Ag states under isolated, unperturbed conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464056
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  • 4
    Electronic Resource
    Electronic Resource
    One- and two-photon fluorescence excitation spectra of the 2 1Ag states of linear tetraenes in free jet expansions (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 4726-4739 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One- and two-photon fluorescence excitation spectra of the S1←S0 transitions of the all-trans isomers of 1,3,5,7-octatetraene, 1,3,5,7-nonatetraene, and 2,4,6,8-decatetraene have been obtained in free jet expansions. Comparison of the one- and two-photon spectra allows the unambiguous identification of electronic and vibronic origins and, for octatetraene and decatetraene, provides clear evidence for molecular inversion symmetry. One-photon spectra show ag progressions built on Herzberg–Teller, bu promoting modes, while two-photon spectra are built on progressions of ag modes starting from the 2 1Ag←1 1Ag electronic origins. In nonatetraene, the absence of inversion symmetry results in an allowed electronic origin in both the one- and two-photon spectra. Nevertheless, bands built on vibronic origins dominate the one-photon spectrum. The S1←S0 spectra of nonatetraene and decatetraene exhibit characteristic splittings of vibronic bands that can be quantitatively explained by the tunneling of the methyl groups through low energy, torsional barriers in the S1 states. Couplings between methyl torsions and low frequency skeletal modes further complicate the optical spectra. Fluorescence lifetimes indicate abrupt onsets of nonradiative decay processes (tentatively attributed to trans→cis isomerization) at ∼2100 cm−1 excess energy. Systematic differences in the energy dependencies of S1 nonradiative decays in the three polyenes can be explained by the higher densities of vibronic states in the methyl-substituted compounds. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469521
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  • 5
    Electronic Resource
    Electronic Resource
    Evidence for quantization of the transition state for cis–trans isomerization (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 9269-9271 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Cis–trans isomerization rates of trans,trans-1,3,5,7-octatetraene (OT) on the first excited singlet state (2 1Ag) potential surface have been obtained as a function of vibrational energy by measuring the fluorescence lifetimes. A stepwise increase in the isomerization rate with increasing energy has been observed, which indicates quantization of the vibrational levels of the transition state for the cis–trans isomerization of a double bond. The energy spacing of 80±10 cm−1 between the first two steps tentatively is assigned to an in-plane bending vibration of the transition state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466680
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  • 6
    Electronic Resource
    Electronic Resource
    Vibronic coupling in polyenes: High resolution optical spectroscopy of all-trans-2,4,6,8,10,12,14-hexadecaheptaene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3360-3365 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution fluorescence and fluorescence excitation spectra of all-trans-2,4,6,8,10,12,14-hexadecaheptaene have been obtained in n pentadecane at 10 K. The most prominent vibronic features, like those in spectra of shorter polyene hydrocarbons, are due to combinations of symmetric carbon–carbon stretching vibrations. These in turn are dominated by a double bond mode whose frequency increases from 1555 to 1782 cm−1 upon electronic excitation (1 1Ag→2 1Ag). This 227 cm−1 increase, the largest yet observed in polyene spectroscopy, can be explained by vibronic coupling between the ground and first excited singlets. The possible role of vibrational mixing due to mutual polarizibilities between carbon–carbon bonds also is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452978
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