pi-conjugated and light emitting poly(4,4'-dialkyl-2,2'-bithiazole-5,5'-diyl)s and their analogues comprised of electron-accepting five-membered rings. Preparation, regioregular structure, face-to-face stacking, and electrochemical and optical properties

Poly(4,4'-dialkyl-2,2'-bithiazole-5,5'-diyl)s (PRBTz, alkyl = methyl (PMeBTz), butyl(PBuBTz), and heptyl (PHepBTz)) and their analogues comprised of 33-150 thiazole rings have been prepared by organometallic polycondensation, and their chemical and physical properties are compared with those of pi-conjugated poly(thiophene-2,5-diyl) (PTh) and poly(pyridine-2,5-diyl) (PPy). Electrochemical n-doping of PRBTz takes place at E degrees = -1.77 to -2.30 V vs Ag/Ag+ and is accompanied by the appearance of a new absorption band in the near-infrared. PMeBTz assumes a relatively stiff structure in solution and shows a large refractive index increment of 0.55 cm(3) g(-1); powder X-ray diffraction analysis of PMeBTz supports a face-to-face type stacking of the polymer chains in the solid;state. All of the polymers show photoluminescence in solutions and in the solid, and an electroluminescence device using PMeBTz as the emitting layer gives emission of light at lambda(max) = 680 nm with 100 cd m(-2) at 8 V. A thin film of PMeBTz gives an optical third-order nonlinear susceptibility chi((3)) of 2.5 x 10(-11) esu, which is larger than observed with PTh and PPy films, and comparison of the chi((3)) value with that (0.3 x 10(-11) esu) of nonregioregular poly(4-methylthiazole-2,5-diyl) (PMeTz) reveals the importance of the regioregular structure of PMeBTz to give the larger chi((3)) value.