Malononitrile derivatives as push-pull molecules: Structure - properties relationships characterization

A series of molecules with a dicyanovinyl acceptor connected with various substituted phenyls as donor blocks were synthesized and characterized. The thermal, electrochemical and photophysical properties of these compounds were investigated and compared. DSC and TGA measurements revealed that all compounds showed high both different melting transitions and the beginning of decomposition. The electrochemical studies did not show significant differences in energy band gap being between 2.41 and 2.55 eV (except for one with carbazole unit), which was also supported by the density functional theory calculations. They emitted light with higher photoluminescence quantum yield in film than in solution. Blends containing the malononitrile derivatives dispersed in a solid matrix consisting of poly(9-vinylcarbazole) and (2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole) emitted with small or high contribution from the host, signaling efficient or incomplete energy transfer from host to guest molecules. Emission of light under external voltage by diodes based on these blends was observed.