The effect of hydration on the spectral luminescence properties of solutions of 2,2 difluoro 4 methylnaphto[2,1 e] 1,3,2 dioxaborine in organic solvents is studied. Quenching of lumi nescence and color changes of the solutions associated with hydration of luminophore molecules were observed. Quantum chemical modeling of the structure of the hydrate complex is carried out.Key words: quantum chemical calculations, density functional theory, difluoroboron β diketonates, luminescence, hydrogen bond. Fluorescent dyes immobilized in polymeric mat rices and capable of "on" and "off" switching their luminescence are promising systems for the design of reversible, reusable luminescence on off optical fiber sensors. 1-3Difluoroboron β diketonates exhibit bright fluore scence in the crystalline state 4 and in solutions, 5-7 thus being promising compounds for use as luminescent dyes for polymers. 8,9 In the present work, we report for the first time on reversible on off luminescence switching of solutions of 2,2 difluoro 4 methylnaphtho[2,1 e] [1,3,2]dioxa borine (1) in organic solvents upon addition of water.There is a number of on off luminescence switching mechanisms, e.g., (i) inversion of nπ-ππ states due to involvement of n electrons of heteroatoms in the forma