Diazobenzo[a]fluorene derivatives as visible photosensitizers for free radical polymerization

Several benzophenazine dyes containing a diazobenzoa]fluorene moiety have been synthesized and characterized by ¹H NMR spectroscopy and mass spectrometry (CI MS). The spectroscopic and electrochemical properties of these dyes were examined. These compounds were evaluated as potential light absorbing chromophores for free radical polymerization. The results are discussed on the basis of the free energy change for electron transfer from the diazobenzoa]fluorene dyes to the electron donors/acceptors. The kinetic studies of the photoinitiated polymerization of trimethylolpropane triacrylate (TMPTA) using electron donors, such as phenylthioacetic acid, phenoxyacetic acid, N-phenylglycine and ethyl 4-N,N-dimethylaminobenzoate, and electron acceptors, such as 1-methoxy-4-phenylpyridinium tetrafluoroborate and 1-ethoxy-2-methylpyridinium hexafluorophosphate, have shown that these dyes are efficient photoinitiators for free radical polymerization in visible light. The heavy atoms present in the chemical structure may lead to excited triplet states within the dye facilitating electron transfer from these states.