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The solvent effect on the position and the shape of the absorption spectrum of peridinin for 12 protic and aprotic solvents as well as the temperature effect for methanol were studied using a solvatochromic theory based on the Onsager sphere cavity model. (Experimental data have been provided by T. Polivka and V. Sundström.) Solvatochromic calculations combined with estimations of orientation broadening of the absorption spectrum by convolution allowed the conclusion that the orientation (dipole-dipole), induction and dispersion solute-solvent interactions reasonably describes the position of the 0-0 frequency. The orientation interactions led to the blue solvatochromic shift, separating them from the induced and dispersion interactions, which produce a red shift. The FWHM of Gaussian of inhomogeneous broadening originated from the fluctuations of orientation interactions was demonstrated to be high (945 cm-1) even for such a nonpolar solvent as hexane. The value of Δμ/cos φ of -18.7 D has been found (Δμ = μ2 - μg, φ is the angle between Δμ and μg). By assigning peridinin to the idealized C2v point group, the large change of dipole moment Δμ of 18.7 D under S2←S0 transition is obtained for peridinin in gas phase. Moreover, the S2-excited state dipole moment μ2 has the opposite orientation relative to that at the ground S0 state μg. The determined gas-phase 0-0 energy of the S2←S0 transition, 22 910 cm-1 (2.84 eV) is employed to calculate the polarizability change between the S0 and S2 states of 376 Å3. The finding for the effective Onsager radius is of 9.4 Å. Obtained results for electrostatic properties of the S2 state are compared with those known from Stark spectroscopy and quantum-mechanical calculations. This journal is © the Partner Organisations 2014. Source

Pavlovich V.S.,Military Academy of Belarus | Lugousky A.P.,Belarusian State University | Stupak A.P.,B. I. Stepanov Institute of Physics
Journal of Applied Spectroscopy | Year: 2015

With the aim of obtaining new fluorescent biomarkers, we have synthesized nanodiamond–dye dyads which form a stable aqueous suspension. In the dyads, by means of nucleophilic substitution of the nitro group, the N-substituted 4-nitro-1,8-naphthalimide was added to the ultradisperse nanodiamonds via a long alkyl chain. We studied the absorption and fluorescence spectra and also the fluorescence decay kinetics for the dyads. We propose that the non-exponential fluorescence decay for the dyads in aqueous suspension is due to two ways to position the plane of the N-substituted 1,8-naphthalimide relative to the plane of the nanodiamond. © 2015 Springer Science+Business Media New York Source

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