Non-reciprocity photochemical behaviour of new 1,2-naphthoquinone-(2)-diazo-sulfonic acid esters

Abstract

1,2-Naphthoquinone-(2)-diazo-4-sulfonic acid esters show specific photochemical behaviour and absorption characteristics, which deviate from that of 1,2-naphthoquinone-(2)-diazo-5-sulfonic acid esters. The 1,2-naphthoquinone-(2)-diazo-5/6/7-sulfonic acid esters show identical absorbance and photochemical behaviours. Bi- and trichromophoric naphthoquinone diazo derivatives (NQD) are characterized by non-reciprocity behaviour, which means that the rate of photolytic cleavage is dependent on the concentrations of the starting compound and intermediates of the photodecomposition, and quantum yields change with the progress of reaction. These interesting experimental results, namely the differences in absorption and photolytic behaviour motivated the preparation and investigation of the model compound, which contains both chromophores, NQD4 and NQD5, para to each other in a benzophenone backbone molecule. The results of kinetic investigations confirm that the exposure of this model compound at 436 nm effects a sequential photolytic mechanism. At this exposure the compound was excited mainly within the NQD5 chromophore, because the NQD4 chromosphore absorbs only slightly at 436 nm. A logical explanation for this effect is the existence of a photophysical process in which the excitation energy is transferred from a local excited NQD-5 substituent (donor) to the NQD-4 substituent (acceptor).