(A) 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 (
F)
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-(10
H)-dipyrrin-1-one, exhibits strong fluorescence (
F=0.68,
em=493
nm,
ex=422
nm in CHCl
3) and UV-Vis absorption (
21000 at 424
nm) in organic solvents. Its diester with (1
S,2
S)-cyclohexanediol is fluorescent and exhibits exciton circular dichroism (
=+15
dm
3·mol
–1·cm
–1,
=432
nm;
=–4
dm
3·mol
–1cm
–1,
=380
nm) that correlates with the
Exciton Chirality Rule.
Keywords. Circular Dichroism; Fluorescence; Exciton; Pyrroles.