Impact of an ortho-cyano group on photophysical properties and performance of OLEDs based on D-A–A type pyrazine push-pull system

A series of novel D–A–A push-pull systems based on a 2-cyanopyrazine acceptor core bearing various electron-donating fragments are synthesized and investigated. The effect of the cyano group on the spectral-luminescent properties of molecules in solvents of different polarities and films obtained by thermal vacuum deposition has been investigated. Fast and delayed luminescence was studied at room temperature and 77K. The energy gap between the S1 and T1 states is estimated. The reasons for the weak thermally activated delayed fluorescence are discussed. It has been found that increasing the efficiency of light-emitting organic diodes up to 20 times took place when a cyano group introduces into fluorophores.