Synthesis and chromophoric properties of symmetrical bis-heteroannelated diketopiperazines: Diimidazo- and dipyrazolo-piperazinediones

Abstract

Several derivatives of the symmetrical diimidazopiperazinedione and dipyrazolopiperazinedione chromophoric systems have been synthesised and their light absorption properties investigated with the aid of PPP-MO theory. In the case of the diimidazopiperazinedione system, yellow to red derivatives can be obtained by introducing amino substituents in the 1,6- or 3,8-positions. The system is appreciably less sensitive than the 9,10-anthraquinone system towards the bathochromic effect of amino substituents, but resultant dyes have molar absorption coefficients 2–3 times greater than those of the anthraquinones, with smaller half-bandwidths. The dipyrazolopiperazinediones show a somewhat greater bathochromic shift when two donor groups are introduced into the 3,8-positions, and (theoretically) the 2,7-positions, but the system is also not as sensitive to donors as the anthraquinone system and dyes have low absorption intensities similar to the anthraquinones.