Light-emitting diodes fabricated from biomolecular compounds

We fabricated ITO/biomolecule/Al junctions using chrolophyll a, cytochrome c, myoglobin, hemin, Vitamin B12. All the junctions worked as organic light-emitting diode (OLED). The quantum efficiencies of the fabricated OLED were of the order of 1 × 10−7 around V = 10 V, and did not seriously depend on whether or not a compound exhibits photoluminescence. Based on the energy diagram of the ITO/cytochrome c/Al junction, we discuss the difference of the EL spectrum from the photoluminescence or absorption spectrum.