The 9-(Z)-configuration was exclusively obtained in the carotenoid polyene chain irrespective of olefination and disconnection methods for terminal ortho-unsubstituted benzene rings. The 2,6-dimethyl substituents in the terminal rings secure an all-(E)-polyene structure. The single molecular conductance of the pure 9-(Z)-carotene was measured for the first time to be 1.53 × 10 ± 6.37 × 10G, whose value was 47% that of the all-(E)-carotene ((3.23 × 10) ± (1.23 × 10) G).

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.

A series of para-phenolic carotenes 1 with ortho- and meta-substitutions were respectively prepared utilizing the benzenesulfonyl protection method, which demonstrated the importance of the ring substituents on their effective conjugation, evaluated by their UV absorption values. The corresponding apo-12′-carotenals 2 were devised to improve the conjugation effect of the para-phenolic radical with the polyene chain by the conjugated aldehyde group. Apo-12′-carotenals 2b and 2c without ortho-substituents exhibited superior antioxidant activities to their corresponding symmetrical carotenes 1 as well as β-carotene and apo-12′-β-carotenal in 2,2′-azino-bis­(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assays.

The synthetic method of tetraphenyl‐substituted all‐E‐carotenes 1 with improved properties of antioxidant and molecular electronic conductance was developed through the formation of tetraphenyl‐substituted all‐E‐apocarotenedial 4. The synthesis highlighted the preparation of novel subunits containing phenyl substituent(s) with E‐configuration starting from the key (E)‐4‐chloro‐2‐phenylbut‐2‐enal (10), utilizing conjugation effect with formyl group or easy recrystallization of sulfone compounds. Sulfone‐mediated coupling methods of Julia and modified Julia–Kocienski olefinations utilizing the subunits were demonstrated to produce tetraphenyl‐substituted apocarotenedials 4. The major all‐E‐forms (73–85 % selectivity) were easily purified by SiO2 chromatography and trituration with Et2O due to the presence of the polar formyl groups. The olefination of all‐E‐apocarotenedials 4 and Wittig salt 5 provided all‐E‐9,9',13,13'‐tetraphenylcarotenes 1.

Tribenzotropone was efficiently synthesized by a ring-expansion method from readily available phenanthrene-9,10-dione via a ringopened diketone as a key intermediate; the diketone was prepared by nucleophilic addition of allyl and vinyl groups, followed by an oxidative ring-opening reaction with lead(IV) acetate. Ring closure by an intramolecular Diels-Alder reaction and subsequent dehydrogenation produced tribenzotropone in 38% overall yield. Ring closure by a MoritaBaylis-Hillman reaction, on the other hand, produced a dibenzo-fused nonanedione in 22% overall yield.