Why biphenyl configuration still matters

More than 40 years ago, Kurt Mislow synthesized restrained biphenyl derivatives, classically resolved them and correlated their absolute configuration with the sign of the Cotton effect. We have encountered biphenyl dyes in mixed crystals and crystalline tissues that were presumably resolved by interaction with chiral crystal facets or by adsorption to biopolymers. Understanding association mechanisms required that we likewise determine the absolute configuration, but inside organized media which traditionally do not reveal optical rotation or circular dichroism because of the dominance of linear anisotropies. We therefore recently invented the first circular extinction imaging microscope that can detect circular dichroism in low-symmetry media, and also a new effect in crystal optics that we call anomalous circular extinction. Here, we show what information can be obtained from dyed, organized substances containing biphenyl derivatives by exploiting this new tool.