π-Conjugated Poly(aryleneethynylene)s Consisting of Salophen and Ni−Salophen Units in the π-Conjugated Main Chain: Preparation and Chemical Properties

π-Conjugated poly(aryleneethynylene)s consisting of N,N′-bis(salicylidene)-1,2-phenylenediamine (salophen) units (Poly-1−Poly-3) and salophen−nickel complex units (Poly-1−Ni) were prepared in high yields by the palladium-catalyzed polycondensation of H−−Ar−−H (Ar = fluorene or 2,5-dialkoxy-p-phenylene) with dibromo compounds of salophen (Br₂−Salophen) and its nickel complex (Br₂−Salophen−Ni), respectively. The Ni-free polymers (Poly-1−Poly-3) showed good solubility in CHCl₃ and THF, had high thermal stability, and exhibited number-average molecular weights (M_n) of 9200−14000 in GPC analysis. The UV−vis spectra of the polymers showed π−π* transition peaks at about 420 nm, which was comparable to those of poly(p-phenyleneethynylene)s. The UV−vis spectrum of Poly-1−Ni exhibited additional intermediate and small peaks at about 480 and 600 nm, which were assigned to a charge-transfer (CT) electronic transition and a d−d transition, respectively. The complexation of Poly-1 with Ni²⁺ proceeded clearly and quantitatively to give Poly-1−Ni, as monitored by UV−vis spectroscopy. Both the Ni-free and Ni-containing polymers were electrochemically active, and CV (cyclic volammetry) scans of the polymers showed a reduction peak of the salophene unit at approximately −2.2 V vs Ag⁺/Ag and an oxidation peak of the salophene unit at about 0.8 V vs Ag⁺/Ag.