We investigate the energy transfer in donor-acceptor systems with reduced spectral overlap to assess the scope for emission colour tunability and the influence of spectral overlap on the luminescence efficiency. We use copolymers derived from poly [2-methoxy, 5-(2'-ethylhexyloxy)-1,4-phenylene vinylene], randomly attaching tetraphenylporphyrin side-chain units. We find that both photoluminescence and electroluminescence are widely tunable via control of the porphyrin concentration, with relatively efficient energy transfer in spite of Limited spectral overlap. We also find that luminescence efficiency is controlled by concentration quenching of the tetraphenylporphyrin, with only a minor effect of spectral overlap. This has implications for electrophosphorescent devices.