White-light electroluminescence from a layer incorporating a single fully-organic spiro compound with phosphine oxide substituents

We have investigated the potential as an OLED emitter of a spiro compound with phosphine substituents initially designed as a host layer for triplet emitters. This is motivated by the fact that the spiro architecture is expected to reduce the detrimental impact of intermolecular interactions, thus allowing for the use of a single-component layer. Moreover, theoretical calculations suggest that this compound displays all features required for a thermally-assisted delayed fluorescence (TADF) behavior. The photophysical properties of the compound in solution are extremely unusual, as illustrated in particular by a dual emission band with relative intensities strongly depending on the experimental conditions. Although no TADF behavior is evidenced in OLED devices, the compound unexpectedly generates a white light signal, which is interpreted as the result of the formation of both intramolecular and intermolecular (exciplex) charge-transfer states.