Systematic Synthesis of Diphenyl‐Substituted Carotenoids as Molecular Wires

A general method for the construction of diphenyl‐substituted carotenoids has been developed through the stereoselective synthesis of dienyl sulfones with a phenyl substituent. Systematic synthetic pathways to the dienyl sulfones were delineated starting from readily available acetophenones with para ‐substituent X of various electronic natures, which provided the carotenoids with diverse physicochemical characteristics. The sulfone olefination method together with the Ramberg–Bäcklund reaction produced a 9,9′‐ cis ‐10,10′‐diphenylcarotene and all‐ trans ‐9,9′‐diphenylcarotenes. Conductance measurements of the all‐ trans carotenoids by the scanning tunnelling microscopy break‐junction method revealed a positional effect of the phenyl groups as well as a polar effect of the phenyl substituent X according to the electronic nature.