KETOCOUMARINS. A NEW CLASS OF TRIPLET SENSITIZERS

Article abstract of DOI:10.1016/0040-4020(82)85104-1

Several derivatives of 3-ketocoumarins were prepared and are shown to have many of the photophysical criteria required for efficient triplet sensitizers.These compounds include 3-aroylcoumarins (1) and 3,3'-carbonyl-biscoumarins (2).The aryl groups in 1 are either phenyl and substituted phenyl derivatives or heterocyclic groups such as thienyl and benzofuryl.The substituents on the coumarin moiety in 1 and 2, if any, are alkoxy or dialkylamino.These compounds, with absorption maxima between 330 and 450 nm, have extinction coefficients in the range of 1E4 to almost 1E5, which is an important criterion for efficient sensitization of thin films of polymers as those used in photoresists and litography.The singlet-triplet intersystem crossing (isc) efficiencies of several derivatives approach unity.In others, however, a radiationless decay process competes with the isc.The decay process is particularly dominant in the assymetrically substituted derivatives of 2, but seems to be considerably supressed in polymeric matrices.The triplet energies of these compounds range from ca. 48 to 60 kcal/mol.Some of these ketocoumarins show phosphorescence spectra that suggest the presence of "frozen-in" rotamers.