Nonadditive Substituent Effects on Expanding Prestrained C-C Bond in Crystal: X-ray Analyses on Unsymmetrically Substituted Tetraarylpyracenes Prepared by a Flow Microreactor Method

Based on space integration using a flow microreactor system, the title unsymmetrically substituted pyracenes with an extremely long C C bond [1.714(2)-1.739(4)angstrom] are readily accessible, whose structures demonstrate nonadditive substituent effects on expanding the polyarylated C-1-C-2 bond in crystal. The bond lengths rather exhibit correlation with the eclipsing degree of the C-sp3-C-sp3 bond, which is more affected by the intermolecular factors such as crystal packing.