Paresh Chandra Ray

First-order hyperpolarizabilities of octupolar aromatic molecules: symmetrically substituted triazines

The first hyperpolarizabilities of some symmetrically substituted triazines have been measured and compared with those of the corresponding symmetrically substituted benzenes. The octupolar triazines have higher quadratic polarizabilities than the corresponding octupolar benzenes. The triazine ring seems to be a better central acceptor than the benzene ring, but if it acts as a donor as in sym-triphenyl triazine, the nonlinearity improves further.

A comparative study of first hyperpolarizabilities of the acidic and basic forms of weak organic acids in water

Dynamic and static first hyperpolarizabilities (β) of a series of benzoic and cinnamic acids in water have been investigated. These acids exist in a mixture of acidic and basic forms in solution. The hyperpolarizability of the basic form is higher than that of the corresponding acid form which is attributed to the red‐shift of the absorption maximum of the basic form relative to that of the acid form. A ZINDO‐correction vector (CV) method including solvent effects through a self‐consistent reaction field (SCRF) for computing β reproduce measured values within experimental errors. Static ab initio hyperpolarizabilities within SCRF are slightly lower than the ZINDO/CV/SCRF β’s. Semiemperical as well as ab initio gas phase calculations show the correct experimental trend in β but their magnitudes are much smaller than the measured values.

Probing molecular self-assembly by hyper-Rayleigh scattering in solution

The formation of a noncovalent self-assembly of melamine and cyanuric acid is probed by the hyper-Rayleigh scattering technique. It is shown that the intensity of the scattered second harmonic light in solution increases significantly as the 1:1 complex of melamine and cyanuric acid is formed. Both the formation and destabilization of the hydrogen-bonded complex between these two molecules can easily be monitored by this technique.

Influence of poling methods on the orientational dynamics of 2-methyL-4-nitro-aniline in poly (methyl methacrylate) studied by second harmonic generation

The magnitude and stability of the induced dipolar orientation of 2-methyl-4-nitroaniline (MNA)/poly(methyl methacrylate) (PMMA) guest/host system is investigated. The chromophores are aligned using both the corona discharge and contact electrode poling techniques. The magnitude of order parameter (also an indicator for the second order nonlinear susceptibility) is measured by recording absorbances of the poled (by the two different techniques) and unpoled PMMA films at different concentrations of MNA. Under the same conditions the corona poling technique creates a higher alignment of molecules along the field direction. The time dependence of the second harmonic intensity of the MNA/PMMA film prepared by the two techniques can be described by a Kohlrausch-Williams-Watts stretched exponential. The temperature dependence of the decay time constant is found to generally follow a modified Williams-Landel-Ferry (WLF) or Vogel-Tamann-Fulcher (VTF) equation. The glass transition temperature seems to be the single most important parameter for determining the relaxation time τ(T).

Second-order polarizability of p-substituted cinnamic acids

First-order hyperpolarizabilities

First hyperpolarizabilities of some push-pull olefins measured by the hyper-Rayleigh scattering technique

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Dissociation constants of some substituted cinnamic acids in protic solvents: measurements by hyper-Rayleigh scattering and potentiometric techniques

of a series of p-substituted cinnamic acids have been measured using the hyper-Rayleigh scattering technique and compared with those of p-substituted benzoic acids.

METALLOPORPHYRINS FOR QUADRATIC NONLINEAR OPTICS

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First-Order Hyperpolarizabilities of Sulfophthalein Dyes

in these acids increases as a function of the donor strength. It increases twice with the increase in the effective chain length. Semi-empirical calculations also support this enhancement. Solvents effects are dealt with at the ab initio level within the self-consistent reaction field approach.

Ka Values of Weak Organic Acids in Protic Solvents Obtained from Their First Hyperpolarizabilities in Solution

Abstract First hyperpolarizabilities of a series of donor-acceptor substituted ethylenes and butadienes have been measured using the hyper-Rayleigh scattering technique. Keeping the donor group fixed as dimethylamino, the second-order nonlinear coefficient β in these aliphatic systems has been measured and is shown to increase as a function of the acceptor strength with the exception of the cyano group, β values of the substituted butadienes are correlated with their bond length alternation parameter 〈 δr 〉 obtained from semi-empirical calculations. It is shown that even in these small push-pull olefins, it is possible to generate a variety of ground state structures by choosing a suitable acceptor with a fixed donor.