Exciton chirality. (A) origins of and (B) applications from strongly fluorescent dipyrrinone chromophores

The origin of exciton interaction and examples of its application to organic stereochemistry are presented. (B) N,N'-Carbonyl-bridged dipyrrinones constitute a new class of highly fluorescent chromophores suitable for investigations of stereochemistry and absolute configuration. N,N'-Carbonylxanthobilirubic acid esters are strongly fluorescent, with a fluorescence quantum yield (phi(F)) similar to 0.8, but produce only weak exciton CD from the trans-1,2-cyclohexanediol template. The ester of an analog with benzoic acid replacing propionic, N,N'-carbonyl-8-(4-carboxyphenyl)-3-ethyl-2,7,9-trimethyl-(10H)-dipyrrin-1-one, exhibits strong fluorescence (phi(F) = 0.68, lambda(em) = 493 nm, lambda(ex) = 422 nm in CHCl3) and UV-Vis absorption (epsilon similar to 21000 at 424 nm) in organic solvents. Its diester with (1S,2S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (Delta epsilon=+15 dm(3).mol(-1).cm(-1), lambda=432 nm; Delta epsilon=-4 dm(3).mol(-1) cm(-1), lambda=380 nm) that correlates with the Exciton Chirality Rule.