Reproducible on–off switching of the light emission from the electroluminescent device containing a spin crossover complex

Abstract To examine the mechanism of a reproducible on–off switching of light emission from a novel organic electroluminescent (EL) device consisting of a spin crossover complex of [Fe(dpp)2](BF4)2 (dpp = 2,6-di(pyrazol-1-yl)pyridine) and chlorophyll a, we have investigated the EL properties of an ITO/chlorophyll a:[Fe(dpp)2](BF4)2/Al device. The comparison with a reference device not containing [Fe(dpp)2](BF4)2 revealed that the introduction of [Fe(dpp)2](BF4)2 results in small threshold voltage and large external quantum efficiency. Moreover, the EL spectra in the low-temperature region, where [Fe(dpp)2](BF4)2 is in the low-spin state, showed the emission from the ITO electrode, suggesting that injected electrons pass through the active layer via [Fe(dpp)2](BF4)2.