UDC 543.42+535.34 IR absorption spectra of indolinospironaphthooxazine (ISNO) are presented. The geometric structure and normal coordinates of the ISNO molecule have been calculated using a quantum mechanical DFT method. The IR spectrum of ISNO in its original spiro form has been interpreted for the first time. Four normal modes in the range 800-1200 cm -1 with the largest amplitudes of C spiro -O bond change are identified. The excited ISNO molecule spiro form may experience photoconversion to the merocyanine form through them.Introduction. Organic photochromic materials hold great promise for application in molecular electronic devices and information processing systems. Factors hindering practical use of photochromic materials include their insufficient photochemical and thermal stability, a poor understanding of the course of molecular structural transformations during the photochromic process, and the fundamental stages in the mechanisms of the phenomenon. Obviously, these issues are interrelated [1][2][3][4][5]. The fabrication of molecular structures with increased photochemical stability such as indolinospirooxazine compounds has prompted researchers to study the photochromic effect in materials based on them [6][7][8][9][10][11].Optical and radiationless transitions in photochromic materials and the mechanisms of intra-and intermolecular interactions that determine the generation and decay of excitations in such molecules must be studied in order to understand thoroughly the photochromism phenomenon [5,11,12]. Information on the properties of vibrational states is important for investigating photochromism and deploying photo-and thermochromic materials because these states are actively involved in the absorption and dissipation of absorbed optical quanta [11,12]. A necessary step in studying the electronic and vibrational transitions is the determination of the characteristics of molecular normal modes (NMs) that are most active in optical and radiationless processes. This must begin with a theoretical and experimental study of the NMs of these molecules in the structure typical of the ground electronic state of the initial spiro form (closed form).Herein the IR spectrum of one of these compounds, indolinospironaphthooxazine (ISNO) or 1,3-dihydro-1,3,3-trimethylspiro[2H-indol-2,3′-[3H]naphtho[2,1-b][1,4]oxazine] [13], in the initial spiro form (Fig. 1) is studied and interpreted based on quantum-mechanical calculations using the DFT method.Experimental. ISNO was synthesized by the literature method [6]. IR spectra were recorded on Specord 75IR and Nexus FT-IR (Thermo Fisher Scientific, USA) spectrophotometers in the range 4000-400 cm -1 with spectral slit

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