We have used fluorescence spectroscopy to study photoconversions of 2-methylphenol (2-MP), , in water when excited by UV radiation from different sources. We discuss the effect of the acidity of the medium and dissolved oxygen on photoconversions of the indicated methylphenols. The photodegradation efficiency for 2-MP and 4-MP decreases in the absence of oxygen. The photoconversion efficiency for methylphenols in alkaline medium is higher when irradiated by light with λ rad = 283 nm, while in neutral medium it is higher when irradiated by light with λ rad = 222 nm.Introduction. This work is devoted to study of the fluorescent properties of some substituted phenols after UV irradiation, and is a continuation of a cycle of investigations on photodecomposition of organic molecules in the phenol class [1]. It was shown earlier [2] that the highest photodegradation efficiency for phenol in water is detected when it is exposed to radiation from a KrCl lamp, and for 4-chlorophenol when exposed to radiation from a XeBr lamp. The aim of this work was to study the luminescent spectral properties of 2-methylphenol (2-MP), 4-methylphenol (4-MP), and 2-amino-4-methylphenol (2-A-4-MP) (Fig. 1) in water for different pH values when exposed to UV light, and also to select a UV radiation source for most efficient photoconversion of the indicated compounds.According to the results of quantum chemical calculations in [3], we can identify the following differences between the photophysical properties of these molecules. When an NH 2 group is introduced into the 2 position of the 4-MP molecule, the energies of the electronic states of the 2-A-4-MP molecule are lowered (see Fig. 1), the oscillator strengths of the S 0 → S n transitions increase compared with 2-MP and 4-MP. Electronic transitions in 2-MP and 4-MP molecules from the ground state S 0 to the excited states S 1 , S 2 , S 3 are accompanied by transfer of electron density from the oxygen atom of the OH group to the carbon atoms of the aromatic ring. Such transfer of electron density promotes an increase in the probability of abstraction of a proton upon excitation. The S 0 → S 1 and S 0 → S 2 transitions in the 2-A-4-MP molecule also occur with participation of the oxygen atom from the OH group, while upon excitation to the S 3 state, electron density transfer from the oxygen atom of the OH group to a carbon orbital no longer occurs. Therefore we should expect differences between the properties of the molecule when it is excited to different electronic states. The most likely mechanism for breaking of the OH bond in methyl-substituted phenols upon excitation up to 50,000 cm -1 (200 nm) is predissociation. The fluorescence quantum yield for 2-A-4-MP in water is lower due to the high efficiency of S 1 -T 3 conversion compared with 4-MP (0.004 and 0.170 respectively).The proposed photolysis products of the selected molecules have been rather well studied by pulsed photolysis and are described in [4][5][6][7][8][9]. It has been established that the OH radicals formed during pho...