The channeled spectra of optically active crystalline layers, (quartz of Maramures was used in our experiments) placed between two identical crossed polarizers, were recorded and the difference Δn<sub>c</sub> = n<sub>l</sub> − n<sub>r</sub> between the crystal refractive indices for circularly polarized radiations to left and to right, respectively, was computed by using the conditions of the minima and maxima of flux density in channeled spectrum. The theory of the phenomena determining the channeled spectra is discussed here. The optical rotatory dispersion of quartz is estimated in the visible range and the obtained results are concordant with those from literature. The quartz optical rotatory dispersion decreases when the wavelength of radiation increases (from blue to red). This kind of measurements is important for industry of optical devices working in polarized light. The method described in this paper is distinguished by rapidity and a large spectral range in which can be applied.
Triazolium ylids are dipolar molecules with separated charges in their ground electronic state; the positive charge is located on one Nitrogen atom belonging to the heterocycle and the negative charge is located near the ylid carbanion. The intramolecular charge transfer from the carbanion to heterocycle gives a visible electronic absorption band, very sensitive to the solvent nature. Its position in the wavenumber scale offers information about the intermolecular interactions in which the ylid molecules are engaged. The spectral study revealed the presence of both universal and specific interactions in solutions of 1,2,4-triazolium ylids with protic solvents. By choosing adequate binary solvents, the contribution of the specific interaction of the weak hydrogen bond between the –OH atomic group of the protic solvents and the ylid carbanion can be estimated. Ternary solutions of the studied ylids achieved with Methanol +Benzene, Water + Ethanol and 1,3 Propanediol + Dimethyl formamide binary solvents are analyzed from spectral point of view and the difference between the potential energies in molecular pairs of the types: 1,2,4-triazolium ylid-protic solvent and 1,2,4-triazolium ylid-non protic were estimated on the basis of the statistic cell model of ternary solutions.
The spectral shifts measured in different solvents are expressed as functions of the solvent macroscopic parameters. The value of the correlation coefficient multiplying the functions of electric permittivity was determined by statistical means. The correlation coefficient depends on the electric dipole moment of the spectrally active molecules. The electro-optical parameters in the ground state of the solute molecules can be approximated by molecular modeling. The excited state parameters are usually estimated using the results obtained both by HyperChem Programme and solvatochromic study. The importance of this approximate method is that it offers information about of the excited state of solute molecule for which our measuring possibilities are very restrictive. The information about the excited electronic state is affected by the limits in which the theories of liquid solutions are developed. Our results refer to two molecules of vitamins from B class, namely B3 and B6.
Pyridazinium ylids are zwitterionic compounds with a visible band resulting from an intramolecular charge transfer from the carbanion towards the heterocycle. The degree of order of ylid molecules in polymer matrices can be estimated by the dichroism of thin films. The visible band intensity measured on two perpendicular directions (one parallel and other perpendicular on the film stretching direction) determines the dichroic ratio, a parameter proportional to the relative number of the oriented ylid molecules along the stretching direction. From the spectral study it results that about 53% of ylid molecules are oriented when the degree of stretching is about 4. This kind of studies contributes to establish the mechanism of the orientation of the lateral polymer chains and also can offer information about the direction of the intramolecular electronic transfer responsible for the visible absorption band appearance.