Thiophene copolymers with benzothiadiazole units

PL and EL emissions from a very low-bandgap copolymer 94 ( g = 1.27 eV) was demonstrated by Swedish researchers [135]. The material has two absorption peaks at 400 and 780 nm and emits light in the NIR region. The PL spectrum of thin films has one peak at 1035 nm which is blue shifted by ca 60 nm on annealing at 200 °C for 10 min. An ITO/PEDOT/94/Ca/Al diode starts to emit the light at very low bias of 1.1 V (A,el = 970 nm). The for a non-optimized device was fairly low (0.03-0.05%)  

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Commonly known as DTBT, the structural unit of 4,7-di(thiophene-2-yl)benzo[c][l,2,5]thiadiazole has been extensively used to construct D-A copolymers of small bandgaps. Shown in Scheme 15.6, the synthesis of DTBT starts with the cyclization of 1,2-diaminobenzene under thionyl chloride to form the central unit, benzothiadiazole (BT). This BT unit is then brominated... 

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