Intermolecular interactions-photophysical properties relationships in phenanthrene-9,10-dicarbonitrile assemblies

Phenanthrene-9,10-dicarbonitriles show various luminescence behaviour in solution and in the solid state. Aggregation patterns of phenanthrene-9,10-dicarbonitriles govern their luminescent properties in the solid state. Single crystal structures of phenanthrene-9,10-dicarbonitriles showed head-to-tail intraplane (or quasi-intraplane) intermolecular interactions and π-stacking patterns with eclipsing of molecules when viewed orthogonal to the stacking plane. The π-stacking interactions were detected in the X-ray structures of phenanthrene-9,10-dicarbonitriles and studied by DFT calculations at the M06–2X/6–311++G(d,p) level of theory and topological analysis of the electron density distribution within the framework of QTAIM method. The estimated strength of the C⋯C contacts responsible for the π-stacking interactions is 0.6–1.1 kcal/mol. The orientation of molecules in crystals depends on the substituents in phenanthrene-9,10-dicarbonitriles. Distinct molecular orientation and packing arrangements in crystalline phenanthrene-9,10-dicarbonitriles ensured perturbed electronic communication among the nearest and non-nearest molecules through an interplay of excimer and dipole couplings. As a result, the intermolecular interactions govern the solid state luminescence of molecules.