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The solvation dynamics following photoexcitation of chlorine dioxide (OClO) in different solvents are investigated by classical molecular dynamics. Following previous work on the aqueous response to OClO photoexcitation [J. Chem. Phys. 118, 4563 (2003)], the present study considers the response of chloroform and cyclohexane; these three liquids present unique solvent environments that differ significantly in both polarity and structure. The study is designed to ascertain the origin of the solvent-invariant homogeneous linewidth associated with OClO photoexcitation and to confirm, at the molecular level, whether the relaxation dynamics are similar across dissimilar solvents due to chance or a common relaxation origin. The results obtained here are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed for all solvents. Analysis demonstrates that the solvation dynamics of OClO are dominated by short-ranged mechanical solute–solvent interactions regardless of the identity and electrostatic properties of the solvent. Low-frequency translational motions dominate the coupling spectrum, and virtually no contribution to energy gap relaxation is achieved through intramolecular solvent motions. The invariant homogeneous linewidth is attributed to the similarity in the primary response of all solvents to OClO photoexcitation. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The solvation dynamics following photoexcitation of aqueous chlorine dioxide (OClO) are investigated by classical molecular dynamics. A total of four OClO/water models are employed, including standard and customized OClO models together with SPC/F and TIP3P water. The simulation results are used to predict the time scale of solvent-induced optical dephasing, and excellent agreement with experiment is observed. The simulations demonstrate that the solvation dynamics of aqueous OClO are dominated by the short-ranged mechanical solute-solvent interactions. When compared to the aqueous solvation of spherical solutes, the solvation dynamics of OClO exhibit a novel effect. The role of the faster translational and librational water motions is suppressed in the dielectric component of the response, but is emphasized in the mechanical response, in stark contrast to the results for other spherical systems. The faster translational motions appear in the mechanical response due to the noncentrosymmetric nature of the OclO-water interaction, enhanced by OclO-water hydrogen bonding. [ABSTRACT FROM AUTHOR]

Recent progress in single-molecule spectroscopy of dyed composite materials is reviewed. In particular, single-molecule studies of dyed polymer films and dye inclusion crystals are described that seek to understand local guest-host interactions and environmental heterogeneity. Single-molecule orientational studies of chromophores in polymer films and mixed crystals are discussed with particular relevance to materials and device applications. Studies of single-molecular reorientational dynamics in polymers in the presence of an electric field designed to establish alignment are described. Static orientational measurements in mixed crystals, wherein alignment is a consequence of crystal growth, reveal a surprisingly wide distribution of molecular orientations. Moreover, the complex photophysics of single molecule in anisomorphous mixed crystals are explored and described in the context of environmental heterogeneity and distributed kinetics. The emerging literature regarding dispersed kinetics observed for individual emitters (e.g. quantum dots, single molecules in polymers, etc.) is reviewed. Finally, the outlook of single-molecule spectroscopy in dye-doped materials is outlined. [ABSTRACT FROM AUTHOR]

Efficient noncentrosymmetric arrangement of nonlinear optical (NLO) chromophores with high first-order hyperpolarizability (β) for increased electro-optical (EO) efficiency has proven challenging as strong dipolar interactions between the chromophores encourage antiparallel alignment, attenuating the macroscopic EO effect. This work explores a novel approach to simultaneously achieve large β values while providing an adjustable dipole moment by linking a strong neutral-ground-state (NGS) NLO chromophore with positive β to a zwitterionic (ZWI) chromophore with negative β in an antiparallel fashion. It is proposed that the overall β of such a structure will be the sum of the absolute values of the two types of chromophores while the dipole moment will be the difference. Molecules 1–3 were synthesized to test the feasibility of this approach. Molecular dynamics calculations and NMR data supported that the NGS chromophore component and the ZWI chromophore component self-assemble to an antiparallel conformation in chloroform. Calculations showed that the dipole moment of 1 is close to the difference of the two component chromophores. Hyper-Rayleigh scattering (HRS) studies confirmed that the first hyperpolarizability of 1 is close to the sum of the two component chromophores. These results support the idea that an antiparallel-aligned neutral-ground-state chromophore and a zwitterionic chromophore can simultaneously achieve an increase in β and a decrease of the dipole moment. [ABSTRACT FROM AUTHOR]