Conjugated Polymers with Main Chain Chirality. 2. Synthesis of Optically Active Polyarylenes

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Abstract

An optically active polyarylene, (R)-3, has been prepared from the palladium-catalyzed Suzuki cross-coupling of an optically active binaphthyl molecule, (R)-2,2‘-bis(hexyloxy)-1,1‘-binaphthyl-6,6‘-diboronic acid, (R)-2, with 1,4-dibromobenzene. GPC analysis of (R)-3 shows Mw = 41 000 and Mn = 20 000 (PDI = 2.0). The specific optical rotation of (R)-3 is [α]D = −289.4° (c = 0.5, THF). The UV spectrum of the polymer displays a strong absorption at λmax = 328 nm. Maximum emissions at 388 and 407 nm are observed in the fluorescence spectrum of (R)-3. The polymer emits strong blue light under a UV lamp. Another optically active polyarylene, (R)-4, was also obtained by the polymerization of (R)-2 with 4,4‘-dibromobiphenyl. GPC analysis shows its molecular weight is Mw = 47 000 and Mn = 14 000 (PDI = 3.4). The specific optical rotation is [α]D = −275° (c = 0.22, CH2Cl2). Polymers rac-3 and rac-4 were synthesized by the polymerization of the racemic monomer rac-2 with either 1,4-dibromobenzene or 4,4‘-dibromobiphenyl. Atomic force microscopic study on the polymer films spin-coated on mica shows interesting surface morphology. Pits and pinholes are observed; however, none of the polymers has long-range order.

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