Novel photo-alignment polymer layer capable of charge transport

Abstract

With the progress of organic electronics, materials possessing various functionalities are attracting much attention. Here we have synthesized a novel photo-alignment polymer composed of a conjugated carbazole main-chain and a coumarin side-chain through nickel(0)-mediated polymerization. Carbazole is a well-known hole transporting material and coumarin is also famous for its good photo-alignment properties. The photochemical reactivity of the coumarin side-chain was monitored by UV vis spectroscopy and the liquid crystal (LC) photo-alignment direction of the polymer film was proved to be perpendicular to the polarization direction of the irradiated UV light. The highest occupied molecular orbital (HOMO) level of the polymer, measured from both cyclic voltammetry and photoelectron spectroscopy, was -5.32 eV. Organic light-emitting diodes (OLEDs) of the configuration [ITO/polymer/NPB/Alq(3)/LiF/Al] showed a higher efficiency (2.17%) and brightness (14 000 cd (.) m(-2)) than a control device due to enhanced charge balance.