Luminescence properties of diamino-dicyano substituted benzene and 1,4-pyrazine

The photophysics of several positional isomers of dicyano-diamino benzenes and 1,4-pyrazines in liquid and frozen solutions has been investigated in several organic solvents. Depending on the relative position of donor and acceptor groups the fluorescence lifetimes and quantum yields change over an order of magnitude and more than a double, respectively. This effect can be rationalized in terms of the relative positioning of amino and nitrile groups and the interplay between singlet and triplet sublevels as a direct consequence of the former.

► Dicyano-diamino benzenes and 1,4-pyrazines photophysics strongly depends on the substituents position.
► Absorption, fluorescence and phosphorescence experiments reveal how and why some of the compounds are very strong emitters.
► It is concluded that differences in charge distribution and intersystem-crossing explains the observed trends.