π-Conjugated polymers with controlled higher-order structures feature molecular recognition, stimuli response, optical anisotropy, and photoelectricity. π-Conjugated polymers containing platinum (Pt)−alkynyl σ-complex moieties in the main chain exhibit intense phosphorescence due to the mixed singlet and triplet excited states. Chirally regulated π-conjugated polymers containing Pt complex moieties have great potential as chiroptically functional materials. The present study deals with the synthesis of Pt-containing novel conjugated polymers by the Sonogashira−Hagihara coupling polymerization of [Pt(4,4′-dibromo-2,2′-bipyridine)((R,R)-2,3-bis(tert- butylmethylphosphino)quinoxaline)(trifluoromethanesulfonate)2] coordinated with 4,4′-dibromo-2,2′-bipyridine/(R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline [(R,R)-QuinoxP*] and 1,4-diethynylbenzene derivatives. The polymers exhibited CD signals derived from (R,R)-QuinoxP* and the conjugated main chain. The simulated CD spectroscopic pattern of a low molecular model compound agreed well with the observed spectra. The TEM images of the polymers in the solid state exhibited dispersed patterns with sizes around 10 nm. Concentrated solutions of the polymers in DMF and CHCl3 exhibited patterns assignable to lyotropic liquid crystals. The present study also deals with the synthesis of novel Pt-containing conjugated polymers by the dehydrochlorination coupling polymerization of dichloro(4,4′-tert-butyl-2,2′-bipyridyl)platinum and dichloro(4,4′-dinonyl-2,2′-bipyridyl)platinum with N-[3,5-bis(4-ethynylphenylethynyl)benzoyl]-L-alanine dodecylamide, and investigation of their chiral secondary structures. The polymers exhibited bisignate CD signals assignable to the main chain chromophore in DMF/MeOH = 50/50 (v/v). The presence of particles of Z-average = 30 nm was confirmed in this solution. These results indicated that the polymers formed chirally regulated aggregates. Single-crystal X-ray analysis of the model compound and DFT calculations were carried out to examine the mode of aggregation of the polymers.

Synthesis and control of the higher-order structures of platinum-containing conjugated polymers

ACS Spring Meeting 2021

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