Two-color two-photon excited fluorescence of 2-methyl-5-tert-butyl-p-quaterphenyl (DMQ): ab initio calculations and experimental determination of the molecular parameters.
The paper presents experimental and theoretical studies of two-photon excitation dynamics in 2-methyl-5-tert-butyl-p-quaterphenyl (DMQ) dissolved in cyclohexane/paraffin. Experimentally, a two-color two-photon (2C2P) excitation by two femtosecond laser pulses at 800 and 400 nm has been used in combination with the time-resolved detection of polarized molecular fluorescence. The fluorescence decay was found to be two-exponential, resulting in the molecular excited state lifetime of 753 ± 10 ps and the rotational correlation time of 724 ± 45 ps. Control over the excited and fluorescent photons polarization has been used for determination from experiment of seven independent molecular parameters. The experimental data were analyzed on the basis of the recent theoretical approach [Shternin, P. S., Gericke, K.-H., and Vasyutinskii, O. S. Mol. Phys. 2010, 108, 813-825] supported by ab initio computations of the DMQ electronic structure and transition dipole moments. The results obtained imply that the two-photon absorption tensor S is mostly diagonal and that the Szz tensor component onto the molecular long axis gives the major contribution of 93%. However, it was also found that a number of different symmetry two-photon transitions related to the dipole moment components dxdz and dydz are excited in the conditions of our measurements.
Polarized Fluorescence in Tryptophan Excited by Two-Photon Femtosecond Laser Pulses
The decay of polarized fluorescence of tryptophan in water-propylene glycol solution two-photon excited by femtosecond laser pulses was explored. Linearly and circularly polarized light in the wavelength band of 385–510 nm was used for excitation. Processing of the experimental fluorescence signals as functions of time and light polarization provided an opportunity to identify two characteristic lifetimes characterizing the fluorescence intensity decay and the rotational diffusion time τrot. The spectral dependences of the anisotropy parameter Ω and anisotropy parameters r for linearly and circularly polarized excitation have been determined. It is shown that the fluorescence temporal dependence is well described by the sum of two exponents with amplitudes a1 and a2 and characteristic times τf1 and τf2 at all wavelengths in the studied spectral range. The experimental dependences of parameters Ω, r, τf1, and a2/a1 are nontrivial, which indicates the complexity of the excitation relaxation processes. The obtained results can be used for interpretation of the experiments and prove of the theoretical models describing the intensity and polarization of fluorescence of tryptophan molecules in solutions and organic compounds under optical excitation.
Fascism in Britain: A History, 1918-1985
Tracing its origins from shortly after the World War I, this book presents a portrait of fascism in the 1930s. It reassesses Mosley's career, describes the reasons for internment in 1940 and the effect it had on leading fascists, exposes the famous Britons who subscribed to fascism, reveals the ominous re-emergence of the tradition after 1945, and explains its remarkable persistence into the l980s.