Characteristics of organic light-emitting devices consisting of dye-doped spin crossover complex films

Two organic light-emitting devices (OLEDs) were fabricated to investigate the mechanism of electroluminescence (EL) switching accompanying the spin transition of [Fe(dpp)2](BF4)2 (dpp = 2,6-di(pyrazol-1-yl)pyridine) observed in an OLED with the structure indium tin oxide (ITO)/[Fe(dpp)2](BF4)2:chlorophyll a/Al, consisting of a chlorophyll a (Chl a)-doped [Fe(dpp)2](BF4)2 film. One OLED consisted of poly(N-vinylcarbazole) (PVK) between an ITO electrode and the active layer, and the other contained the electron transporting dye Nile Red (NR) as an emitting dopant material instead of the hole transporting Chl a. In both devices ITO/PVK/[Fe(dpp)2](BF4)2:Chl a/Al and ITO/[Fe(dpp)2](BF4)2:NR/Al, EL emission from the dye compound was observed, irrespective of the spin state of [Fe(dpp)2](BF4)2. It was determined that the EL switching accompanying the spin transition was dominated by a change in the molecular orbital level concerning electron transport in [Fe(dpp)2](BF4)2. Highlights ► Organic light emitting devices containing a spin crossover complex were fabricated. ► Emission characteristics with different structures and dyes were explored. ► Electron injection into dye is a key for the on/off reproducible emission switching. ► Change in the molecular orbital energy level dominates the emission switching. ► Spin crossover complex is a valid tool for controlling characteristics of devices.