The photostability for 2,5-diphenyloxazole (PPO) in diffrent solvents and 2-(4 pyridyl)-5-phenyloxazole (4PyPO) under XeCl laser excitation (l _las=308 nm, E_las=40 mJ, t _FWHM=10 ns) in rectangular ceel into resonator has been investigated. The phototransformation quantum yield - j and yields of the final photoproducts - P_i , also half life time - R₅₀ have been measured.

Experimental confirmations of the PPO photodissociation mechanism, disscussed in [1], are represented in this paper.The PPO phototransformations initiate from C-O bond of the oxazole cycle disruption by preleminary bonding of the electron density on nitrogen atom excess has been showed in [1,2]. Two photoproducts are formed in these transformations: photoproduct P_1, absorbing in the more short wavelength, than PPO, and P₂, absorbing in lasing region.

There is observed 5-7 short-dated increasing of PPO quantum yield of the phototransformation by the increasing proton concentration in solution (addition of H₂SO₄) . Simultaneously, PPO phototransformation yield in cyclogexene is 10 times less then in ethanol. It is known that probability of the cation forming by proton connection from solution to nitrogen atom in S₁ state is increased [3]. Therefore, these facts are the acknowlegment of the point of view, discussed in [1].

Using CCl₄ as the solvent for PPO also increases on 10 times its phototransformation quantum yield. These facts are explained the increasing of PPO k_st in CCl₄ and allowed to concluse, that the oxazole cycle photodissociation origin through triplet p s * states by predissociation mechanism.

Spectral display of phenyl -(PPO) and pyridylsubstituted oxazole - (4PyPO) phototransformation is similarly. Foregoing point of view supposes, that substitution phenyl cycle to pyridyl (i.e. PPO® 4PyPO) should be decrease excess of nitrogen electron density, because pyridyl is more electron acceptor than phenyl cycle. This should be decrease solvent effect and also 4PyPO k_ST and phototransformation quantum yield in ethanol comparative PPO, also it is confirmed in the experiments.

The increasing of the exciting pulse duration from 10 to 40 and 80 ns leads to the rising P₂ yield and decreasing laser life time - R₅₀, which is correlated with P_2, j is not substantial changed. It is concluded, that “longwave” photoproduct is the final photoproduct, which is formed from intermediate longlived particles (radicals, photocations etc., t _FWHM@ ms). These particles are formed in process of the cycle disruption.

The increasing of the exciting intensity to 40 - 50 MW/cm² leads to the increasing of 4PyPO phototransformations and to the decreasing laser life time. The reasons of this behavior are discussed.

1.Mayer G.V., Basyl O.K., Artjukhov V.Ja. Khimija vysokich energii ,1996, v.30, N4, p.280

2.Krivosheev Ja. V., Sinitskaja I.P., Faisi N.Kh., Plotnikov V.G. Khim. fisika, 1990,v.9, N5, p.714.

3.Kuznetsova R.T., Samsonova L.G. Zhurnal prikladnoi spektroskopii, 1989, v.50, N3, p.508.