π-Conjugated poly(pyrimido[5,4-d]pyrimidine-2,6-diyl)s with two different alkylamino groups: Synthesis, chemical properties, and structure

New π-conjugated pyrimidopyrimidine polymers with two different alkylamino groups at C4 and C8 positions, PPympym(4-NH-n-C8H17-8-NHR) (R = n-C4H9, n-C6H13, n-C12H25, and n-C16H33), were prepared by dehalogenation polycondensation using nickel zerovalent complex in high yield. The obtained polymers were partly soluble in organic solvents such as chloroform. A chloroform soluble part of PPympym(4-NH-n-C8H17-8-NH-n-C16H33) showed a number-average molecular weight of about 3,000 in GPC analysis. UV–vis spectra of the polymers in CHCl3 showed a π–π* absorption peak at about 450 nm, and the peak position shifted by 30 nm to a longer wavelength in film. The polymers showed photoluminescence both in solution and in film. Cast films of the polymers were electrochemically reduced at about −2.3 V vs. Ag+/Ag. XRD patterns of the polymers revealed the polymers took an end-to-end packed structure.