Silole-containing polyacetylenes. Synthesis, thermal stability, light emission, nanodimensional aggregation, and restricted intramolecular rotation

We synthesized three substituted polyacetylenes carrying 1,2,3,4,5-pentaphenylsilolyl (PS) pendants, i.e., -[HC=C(PS)](n)- (1), -{HC=C[(CH2)(9)OPS]}(n)- (2) and -(C6H5)C=C[(CH2)(9)OPS]} (n)- (3), and succeeded in turning polymers 2 and 3 from weak luminophors into strong emitters by external stimuli of aggregation and cooling. The silolylacetylene monomers HCequivalent toCPS (10), HCequivalent toC(CH2)(9)OPS (11), and C(6)H(5)Cequivalent toC(CH2)(9)OPS (12) were polymerized by NbCl5- and WCl6-Ph4Sn catalysts, which gave high molecular weight polymers in high yields (M-w up to similar to70 x 10(3) Da and yield up to similar to80%). The structures and properties of the polymers were characterized and evaluated by IR, UV, NMR, DSC, TGA, PL, EL, and nanoparticle size analyses. The polymers were thermally stable and lost little weights when heated to similar to350 degreesC. Whereas all the polymers were practically nonluminescent when molecularly dissolved, polymers 2 and 3 became emissive when aggregated in poor solvents or when cooled to low temperatures. Restricted intramolecular rotation or twisting of the silole chromophores in the solid nanoaggregates or at the low temperatures may be responsible for the aggregation- or cooling-induced emission. A multilayer electrolumineseence device using 3 as an active layer emitted a blue light of 496 nm with maximum brightness, current efficiency, and external quantum yield of 1118 cd/m(2), 1.45 cd/A, and 0.55%, respectively.