Synthesis, Optical and Electrochemical Properties of Isomeric Dibenzophenanthroline Derivatives

Acid‐catalysed Friedländer cyclization of 2‐aminobenzophenones with 1,2‐, 1,3‐, and 1,4‐cyclohexadiones, followed by aromatization, has been used to prepare dibenzophenanthrolines (DBPs) containing 1,10‐, 1,7‐ and 4,7‐phenanthroline units, whose optoelectronic properties have been compared. The LUMO energies for all isomers were similar but the 4,7‐isomers possessed significantly higher HOMOs than the other isomers, resulting in them having smaller HOMO‐LUMO energy gaps. Compared with 1,10‐DBP isomers, the emission of 1,7‐DBPs is strongly quenched due to efficient charge transfer. The 4,7‐DBP isomers show strongly enhanced photoluminescence due to excimer formation but appear to be less photostable due to their higher HOMO levels. Bis(phenylethynyl)‐substituted derivatives demonstrated improved solubility and stronger luminescence properties than their unsubstituted analogues.