Photochemical Reaction of Nalidixic Acid in Methanol
The photochemical reactions of methanolic nalidixic acid (NAL) solution in the absence and in the presence of air have been investigated using 300 nm UV light. From the reactions, 1-ethyl-7-methyl-4-oxo-4-hydro-1,8naphthyridine (EMDN), formic acid, and formaldehyde are produced. In the presence of air, hydrogen peroxide is also detected along with the products listed above. The presence of oxygen during the irradiation of methanolic NAL solution effects on the product yield. The initial quantum yields of the products and of the NAL decomposition are determined. Possible reaction pathways for the photochemical reaction are suggested on the basis of the products analysis.
Photolysis and quantum-chemical calculations of the nalidixic acid radical states
The nalidixic acid transient spectra were analyzed and the scheme of photo-conversion of the acid was suggested. At a large delay of laser pulses the transient absorption spectra contain the bands due to the dissociation of the products of the cation- and anion-radical photodecomposition in the micro- and millisecond range. By quantum-chemical calculations we revealed that at the transition to the ion-radical state a proton migration occurs subsequent to the movement of the center of gravity of the negative charge. The phototransformation of nalidixic was found to proceed with a TICT-effect.
Physical Properties of Excited States: A General Method for Measuring Triplet—Triplet Extinction Coefficients, Singlet—Triplet Intersystem Crossing Efficiencies, and Related Parameters
The quantitative measurement of the various radiative and nonradiative deactivations of electronically excited states is the main purpose behind studies of photophysics and photochemistry. This objective is far from being achieved for any molecule. In this article we describe a general method for measuring two important photophysical parameters, molar extinction coefficients of triplet excited states, ϵT, and quantum yields of formation of lowest triplet, ΦT. Tabulations of all the triplet extinctions and singlet-triplet intersystem crossing efficiencies that have been thus measured to date are also given. A knowledge of these constants allows one to determine a variety of other parameters describing electronically excited molecules and their degradation, for instance: molar extinction coefficients of first excited singlet states, quantum yields of internal conversion, rate constants of intersystem crossing S1 → T1? internal conversion S1 → S0, or triplet-triplet annihilation.