Density dependence of optical Kerr lens signals in neat N2O and CO2

Bürsing, Reinhard; Lenzer, Thomas; Oum, Kawon

doi:10.1016/j.chemphys.2006.11.011

Cited by 5 publications

(9 citation statements)

References 30 publications

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“…This eliminates birefringence effects and prevents changes in the beam polarization. 4 For population relaxation measurements, the relative polarization of the pump and probe beams was adjusted to 54.7°(magic angle) to avoid any contribution from orientational relaxation. Time-dependent anisotropies were determined from additional measurements using parallel and perpendicular relative polarization of the pump and probe beams.…”

Section: Methodsmentioning

confidence: 99%

“…A few measurements were also carried out at the probe wavelength 780 nm to investigate if characteristic stimulated emission (SE) was present in SCFs, which would be a signature of ICT character. 18 Tables S1 and S2): Supercritical CO 2 at 323 K (b) and 308 K (9), supercritical CF 3 H at 323 K (O) and 308 K (0), nonpolar organic solvents (2), and polar organic solvents (4). Dotted lines are linear fits to the data sets in supercritical CO 2 at 323 K and nonpolar organic solvents (see text).…”

Section: Transient Absorption Signals 321 12′-apo--caroten-12′-almentioning

confidence: 98%

“…Such a behavior is frequently described in the framework of hydrodynamic models of the Stokes-Einstein-Debye (SED) type. 4,49,50 The modified SED equation is given as…”

Section: Orientational Relaxation In Supercritical Fluids Inmentioning

confidence: 99%

“…The most important feature of a supercritical fluid is the tunability of its physical properties without changing the chemical nature of the solvent. Thus, solvent properties such as density, diffusivity, capacity for solutes, viscosity, refractive index, and dielectric constant can be easily and continuously changed by the use of SCFs simply by adjusting temperature and pressure. − Specifically, much lower solvent polarizabilities can be reached in SCFs compared to standard organic solvents, allowing, e.g., to shift the electronic S 0 → S 2 transition of carotenoids to higher energies not accessible by conventional solvents. Such a strategy, for instance, enabled reliable extrapolations of the S 0 → S 2 0−0 transition of several C 40 carotenoids toward the gas-phase limit …”

Section: Introductionmentioning

confidence: 99%

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Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H

2008

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The ultrafast excited-state dynamics of the two carbonyl carotenoids 12'-apo-beta-caroten-12'-al (12'C) and 8'-apo-beta-caroten-8'-al (8'C) have been investigated in supercritical (sc) fluids by femtosecond transient absorption spectroscopy. CO2, N2O, and CF3H were employed as solvent media over the pressure range 85-300 bar and at the temperatures 308 and 323 K. The carotenoids were excited to the S2 state at 390 nm, and the subsequent dynamics were probed at different wavelengths in the UV-vis (390, 545, 580, 600, and 650 nm) and near IR (780 nm) regions. Stimulated emission in the near IR signaled the presence of a state with intramolecular charge transfer character (S1/ICT). For 12'C in scCO2 and scN2O, the internal conversion (IC) time constant tau1 for the S1/ICT --> S0 transition showed no systematic pressure dependence and yielded an average value of 190 ps. This is slightly smaller than the values in nonpolar organic solvents (ca. 220 ps) found in our previous studies and probably due to the substantial quadrupole moment of the nondipolar CO2 and the small dipole moment of N20, which might slightly stabilize the S1/ICT state relative to S0. This results in an acceleration of the nonradiative rate in the simple framework of an energy gap law approach. In polar CF3H, a pronounced acceleration of the internal conversion rate was observed with increasing pressure, which can be explained by the polarity increase, as characterized by the parameter deltaf = (epsilon - 1)/(epsilon + 2) - (n2 - 1)/(n2 + 2). We find scCF3H to be the first solvent where the S1/ICT state of 12'C does not decay in a monoexponential fashion. This is most likely attributed to time-dependent solvation of the S1/ICT state, vibrational cooling, or conformational relaxation processes in 12'C. In addition, we studied the dynamics of the longer conjugated species 8'C, where the decays of all transients in scCO2 and scCF3H could be described well by monoexponential fits, in good agreement with previous results in organic solvents. Anisotropy decays from polarization spectroscopy of the 12'C species provided orientational relaxation time constants which were increasing with viscosity. The values in scCO2 were extrapolated to a free rotor time of 4.6 ps, which is in good agreement with a value of 5.2 ps calculated on the basis of the rotational constants. We also report on pressure- and temperature-dependent steady-state absorption spectra of the two apocarotenals in scCO2, scN2O, and scCF3H. The band position of the S0 --> S2 transition correlates well with solvent polarizability, but--in contrast to our previous study of C40 carotenoids--a substantial influence of polarity was also observed. Specifically, we found indications for solvent clustering, resulting in a saturation of the solvent shift at lower densities.

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Section: Methodsmentioning

confidence: 99%

Section: Transient Absorption Signals 321 12′-apo--caroten-12′-almentioning

confidence: 98%

“…Such a behavior is frequently described in the framework of hydrodynamic models of the Stokes-Einstein-Debye (SED) type. 4,49,50 The modified SED equation is given as…”

Section: Orientational Relaxation In Supercritical Fluids Inmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H

2008

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“…This setup has been used previously in our transient lens (TL) and transient absorption (TA) experiments. 13,30,31 Briefly, a mode-locked Ti:sapphire oscillator pumped by a Nd:YVO 4 laser was used to generate pulses at 850, 860 or 890 nm with a repetition rate of 82 MHz and an average laser power of about 1.0À1.5 W. A dichroic mirror was used to split the laser beam into two parts. One part passed through an acousto-optic modulator (AOM, operating at a frequency of 2 MHz provided by a pulse generator) and was subsequently frequencydoubled in a LBO crystal to generate an intensity-modulated pump beam (425, 430 or 445 nm) with pulse energies o0.1 nJ.…”

Section: Near Ir Transient Absorption/stimulated Emission Measurementsmentioning

confidence: 99%

Solvent-dependent ultrafast internal conversion dynamics of n′-apo-β-carotenoic-n′-acids (n = 8, 10, 12)

Stalke

Wild

Lenzer

et al. 2008

Phys. Chem. Chem. Phys.

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The ultrafast internal conversion dynamics of 12'-apo-beta-carotenoic-12'-acid (12'CA), 10'-apo-beta-carotenoic-10'-acid (10'CA) and 8'-apo-beta-carotenoic-8'-acid (8'CA) have been investigated by femtosecond pump-probe spectroscopy. The three apocarotenoic acids were excited to the S(2) state with different excess energies. Time constants tau(1) for the IC process S(1)/ICT --> S(0) were measured by probing the dynamics at 390 nm (S(0) --> S(2)), 575 nm (S(1)/ICT --> S(n)), 850, 860 and 890 nm (S(2) --> S(n) and S(1)/ICT --> S(0)). In nonpolar solvents, the observed reduction of the tau(1) values with increasing conjugation length of the acids is consistent with a reduction of the energy gap between the S(1)/ICT and S(0) states. The values are in good agreement with those of the corresponding apocarotenals studied previously in our groups. In polar solvents, a pronounced reduction of tau(1) values was observed for 12'CA, however the behavior was different from that observed for the respective aldehyde 12'-apo-beta-caroten-12'-al studied previously: First, the degree of tau(1) reduction in methanol was milder for 12'CA (218 --> 55 ps) than for 12'-apo-beta-caroten-12'-al (220 --> 8 ps). Secondly, for 12'CA the plateau of solvent independent tau(1) values extended further into the mid-polar range (up to 0.5 on the Deltaf scale) than previously observed for the 12'-aldehyde. For 10'CA the polarity effect on the tau(1) values was weaker ( approximately 71 ps in n-hexane and 34 ps in methanol) and for 8'CA it disappeared completely ( approximately 24 ps averaged over all solvents). The polarity-induced reduction of tau(1) is likely due to the stabilization of an intramolecular charge transfer state in polar solvents. This S(1)/ICT state is also responsible for the stimulated emission in the near IR, which has been observed in this specific class of carotenoids with a terminal carboxyl group for the first time. The occurrence of stimulated emission in the near IR region is also consistent with the steady-state fluorescence spectra which are reported along with the absorption spectra of these species. Possible reasons for the different behavior of the apocarotenoic acids compared to the respective aldehydes are discussed.

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Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin

Lenzer¹,

Schubert²,

Ehlers³

et al. 2009

Archives of Biochemistry and Biophysics

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Density dependence of optical Kerr lens signals in neat N2O and CO2

Cited by 5 publications

References 30 publications

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H

Solvent-dependent ultrafast internal conversion dynamics of n′-apo-β-carotenoic-n′-acids (n = 8, 10, 12)

Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin

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Density dependence of optical Kerr lens signals in neat N2O and CO2

Cited by 5 publications

References 30 publications

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO2, N2O, and CF3H

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO2, N2O, and CF3H

Solvent-dependent ultrafast internal conversion dynamics of n′-apo-β-carotenoic-n′-acids (n = 8, 10, 12)

Femtosecond pump-supercontinuum probe and transient lens spectroscopy of adonixanthin

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Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H

Excited-State Dynamics of 12′-Apo-β-caroten-12′-al and 8′-Apo-β-caroten-8′-al in Supercritical CO₂, N₂O, and CF₃H