Synthesis of oligofluorenes by endcapping

An efficient one-step synthesis of 9,9-di(2-ethylhexyl)-2,7-fluorene oligomers via an endcapping reaction is reported. Controlled endcapping demands a full conversion of functional groups and thus the Yamamoto reaction was chosen as the aryl-aryl coupling method. SEC analysis showed that the endcapping is complete. The molecular weights were adjusted in the range from 1300 to 3800 g mol^-1 by different amounts of endcapper. The mixtures exhibit broad mesophases and the transition temperatures strongly increase with molecular weight. In the series of oligomers reported here, clearing temperatures between 57°C and over 360°C could be realized.