1-Bromo-2-ethylhexane-d17 is labelled 1-Bromo-2-ethylhexane which was used in the synthesis of methoxy-4-(2-ethylhexyloxy)benzene, photovoltaic conjugated polymer, having benzo[1,2-b:4,5-b′]difuran building block and 1-bromo-4-(2′-ethylhexyloxy)benzene.