Vibrational Spectra of the Closed Form of a Molecule of Indoline Spiroanthraceneoxazine

Abstract

In an approximation of the generalized valence force field, the frequencies and forms of the normal vibrations of the free molecule of spiroanthraceneoxazine (SAO) are calculated. The vibrational spectra of SAO are measured: the IR absorption spectra in an NaCl disk and the Raman spectra in a KBr disk. The calculated and experimental data were correlated with the aid of a method of refined initial data. The results obtained agree with the calculated and experimental spectra of model and related compounds.Keywords: vibrational spectroscopy, generalized valence force field of a molecule.Introduction. The literature devoted to studying the photochromy of indoline spirocompounds completely lacks calculations of the normal vibrations of these compounds. In [1], the results of a purely empirical investigation of their vibrational spectra are presented. It is known that photochromic processes proceed with participation of vibrational and vibronic states [1,2]. Therefore, the practical creation of photochromic materials based on the molecules of spirocompounds requires the study of vibrational and vibronic states. An adequate solution of this problem is possible only by way of extensive theoretical and experimental investigation.In the present work, an attempt is made at a theoretical and experimental investigation of the normal vibrations of the free molecule of 1′,Computational and Experimental Techniques. SAO molecules were synthesized by the technique suggested in [3]. The frequencies and forms of normal vibrations of the free molecules were determined using the program of calculation of the frequencies and forms of normal vibrations in the approximation of the generalized valence force field. This approximation has been applied in an enormous number of works [see, e.g., [4][5][6]). The choice of the equilibrium nuclear configuration of the free molecule of SAO was made with the aid of the "OUP Molecular Modeling Package" program. The natural coordinates selected as well as valence and deformation ones are presented in Fig. 1. Proceeding from the validity of the condition of the transferrability of the force constants of identical nuclear groupings entering into different molecules [5] and from the literature data, we have selected the elements of the matrices of force constants. The first calculation of the frequencies and forms of the normal vibrations of SAO was performed on the basis of calculated parameters of the nuclear configuration of the free molecule and the force matrix elements selected from the literature data [6][7][8]. To attain a more precise agreement between the calculated and experimental frequencies, variation of the values of force constants was applied. Subjected to variation were the force constants of natural coordinates the changes in which yield the greatest contribution to the form of vibrations (potential energy distribution (PED)). Here, the geometric parameters of the molecule did not change. The difference of ν cal from ν exp was reduced to a value of the order of the accuracy value wi...