New Soluble, Coplanar Poly(naphthalene-2,6-diyl)-Type π-Conjugated Polymer, Poly(pyrimido[5,4-<i>d</i>]pyrimidine-2,6-diyl), with Nitrogen Atoms at All of the <i>o</i>-Positions. Synthesis, Solid Structure, Optical Properties, Self-Assembling Phenomena, and Redox Behavior

Abstract

New n-type π-conjugated poly(pyrimido[5,4- d ]pyrimidine-2,6-diyl)s with a poly(naphthalene-2,6-diyl)-type structure and alkylamino substituents were prepared by dehalogenative polycondensation using a zerovalent nickel complex in 90−98% yield. The polymer is considered to have a coplanar π-conjugated main chain and a strong tendency to form a π-stacked structure, as judged from its CPK molecular model, UV−vis data, photoluminescence data, and XRD data. The obtained polymers were soluble in organic solvents and a polymer with N -octylamino substituents showed a number-average molecular weight, M n, of about 8000 in GPC analysis. Other polymers showed analogous M n values. The UV−vis spectra of the polymers gave a main absorption peak at about 450 nm, which was shifted by about 130 nm to a longer wavelength compared to those of corresponding monomeric compounds. The degree of the red shift was larger than those observed with other analogous poly(naphthalene-2,6-diyl)-type π-conjugated polymers, and the large red shift was attributed to the coplanar structure of the polymer. UV−vis and photoluminescence data revealed a strong tendency for the polymer to form a self-assembled structure. Powder X-ray diffraction analysis indicated that the polymers took an end-to-end packing mode. Electrochemical reduction (or n-doping) of the polymers proceeded with an E pc of about −2.3 V vs Ag + /Ag.