Phosphorus Copies of PPV: π-Conjugated Polymers and Molecules Composed of Alternating Phenylene and Phosphaalkene Moieties

摘要

A new class of π-conjugated macromolecule, poly(p-phenylenephosphaalkene) (PPP), is reported. PPPs are phosphorus analogues of the important electronic material poly(p-phenylenevinylene) (PPV) where P=C rather than C=C bonds space phenylene moieties. Specifically, PPPs [—C_6R_4-P=C(OSiMe_3)—C_6R'_4-C(OSiMe_3)=P—]_n (1: R = H, R' = Me; 11: R = Me, R' = H) were synthesized by utilizing the Becker reaction of a bifunctional silylphosphine, 1,4-C_6R_4[P(SiMe_3)_2]_2, and diacid chloride 1,4-C_6R'_4[COCI]_2. Several model compounds for PPP are reported. Namely, mono(phosphaalkene)s R—P=C(OSiMe_3)—R' (4: R = Ph, R' = Mes; 7: R = Mes, R' = Ph), C-centered bis(phosphaalkene)s R—P=C(OSiMe_3)—C_6R'_4— C(OSiMe_3)=P—R (5: R = Ph, R' = Me; 8: R = Mes, R' = H), and P-centered bis(phosphaalkene)s R— C(OSiMe_3)=P-C_6R'_4-P=C(OSiMe_3)-R (6: R = Mes, R' = H; 10: R = Ph, R' = Me). Remarkably, selective Z-isomer formation (i.e., trans arylene moieties) is observed for PPPs when bulky P-substituents are employed while E/Z-mixtures are otherwise obtained. X-ray crystal structures of Z-7, Z,Z-8, and Z,Z-10 suggest moderate π-conjugation. The twist angles between the P=C plane and unsubstituted arenes are 16°-26°, while those between the P=C plane and methyl-substituted arenes are 59°-67°. The colored PPPs and their model compounds were studied by UV/vis spectroscopy, and the results are consistent with extended jr-conjugation. Specifically, weakly emissive polymer E/Z-1 (Amax = 338 nm) shows a red shift in its absorbance from model E/Z-4 (λ_(max) = 310 nm), while a much larger red shift is observed for Z-11 (λ_(max) = 394 nm) over Z-7 (λ_(max) = 324 nm).