PHOTOPHYSICAL PROPERTIES OF 3,5-DIACETYL-1,4-DIHYDROLUTIDINE IN SOLUTION - APPLICATION TO THE ANALYSIS OF FORMALDEHYDE

Formaldehyde, which is a generally occurring pollutant in the atmosphe re and in building materials, can easily be determined by colorimetry or fluorimetry after derivatization to 3,5-diacetyl-1,4-dihydrolutidin e (DDL) according to the Hantzsch reaction. Owing to the fact that the photophysical properties of DDL are to date widely unknown, the absor ption and fluorescence behaviours as weil as their changes under the i nfluence of heat or irradiation have been investigated. From solvent-d ependent measurements an increase in the dipole moment upon excitation is evident. In solvents of comparable polarity the spectra are more r ed shifted in protic media, which is probably due to hydrogen bonding. The fluorescence quantum yield was determined as phi(i)(20 degrees C) =0.005 in aqueous solution and was found to be strongly dependent on t emperature. The activation energy En for non-radiative decay was deter mined according to an Arrhenius-type relationship. DDL decomposes on e xposure to heat or light. The thermal degradation shows deviations fro m first-order kinetics and follows the time equation for an autocataly tic reaction. The quantum yield of the photochemical degradation was d etermined as Phi=(2-3)x10(-3).