Synthesis of Polymers with Alternating Organosilanylene and Oligothienylene Units and Their Optical, Conducting, and Hole-Transporting Properties

Polymers with alternating mono-, di-, or trisilanylene units and 2,5-oligothienylene groups, [(SiR2) x (C4H2S) m ] n (R = Me, Et, x = 1−3, m = 2−5), were synthesized and their optical, conducting, and hole-transporting properties were investigated. The UV absorption and emission maxima of the polymers shift to lower energies as the number of thienylene groups (m) between the silanylene units increases, while they are little affected by the silicon chain length (x). When the polymer films were exposed to FeCl3 vapor, semiconducting films with the conductivities of 1.3 × 10-4−2.3 × 10-1 S/cm were obtained. The conductivities tend to increase with m but decrease with increasing x. The double-layer-type EL devices were fabricated using some of the polymers (x = 1, m = 3−5; x = 2, m = 4) as the hole-transporting layer and tris(8-quinolinolato)aluminum(III) (Alq) as the electron-transporting-emitter layer. Reducing the number of m and x resulted in a high-voltage shift in the turn-on voltage and a decrease in the maximum current density of the device. The highest luminance of 2000 cd/m2 was obtained from a device based on the disilanylene−tetrathienylene alternating polymer (x = 2, m = 4).