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

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 [C6R4PC(OSiMe3)C6R‘4C(OSiMe3)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-C6R4[P(SiMe3)2]2, and diacid chloride 1,4-C6R‘4[COCl]2. Several
model compounds for PPP are reported. Namely, mono(phosphaalkene)s RPC(OSiMe3)R‘ (4:  R =
Ph, R‘ = Mes; 7:  R = Mes, R‘ = Ph), C-centered bis(phosphaalkene)s RPC(OSiMe3)C6R‘4C(OSiMe3)PR (5:  R = Ph, R‘ = Me; 8:  R = Mes, R‘ = H), and P-centered bis(phosphaalkene)s RC(OSiMe3)PC6R‘4PC(OSiMe3)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 π-conjugation. Specifically, weakly emissive polymer E/Z-1 (λmax = 338 nm) shows a red
shift in its absorbance from model E/Z-4 (λmax = 310 nm), while a much larger red shift is observed for
Z-11 (λmax = 394 nm) over Z-7 (λmax = 324 nm).