Alternating 2,7- and 3,6-linked carbazole copolymers as wide band gap energy transfer donors

An alternating copolymer comprising 3,6-linked-9-(2-ethylhexyl)-9H-carbazole and 2,7-linked-3,6-dimethyl-9-(2-hexyldecy)-9H-carbazole has been prepared using Suzuki cross-coupling conditions. The polymer was characterised by nuclear magnetic resonance spectroscopy, UV–Vis absorption spectroscopy, fluorescence spectroscopy and its weight-average molecular weight was estimated using gel permeation chromatography. The polymer is thermally stable up to 420 °C and displays a wide band gap (3.2 eV) and a narrow emission band at 400 nm with a full width at half maximum of 56 nm. Electroluminescence studies indicated that the polymer emitted principally blue light when blended with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole and was found to be a good energy transfer donor to bis(2-(2′-benzothienyl)-pyridinato-N,C3′)iridium (acetylacetonate) and provided devices with an efficiency of 0.1 cd/A, and a turn-on voltage of 5.6 V.