Introduction of a 4-Hexyl-2-thienyl Substituent on Pyridine Rings as a Route for Brightly Luminescent 1,3-Di-(2-pyridyl)benzene Platinum(II) Complexes

The synthesis and characterization of two new complexes, namely Pt(1,3-bis(4-(4-hexyl-2-thienyl)-pyridin-2-yl)-5-mesitylbenzene)Cl and Pt(1,3-bis(4-(4-hexyl-2-thienyl)-pyridin-2-yl)-5-(2-thienyl)benzene)Cl, are reported. Both exhibit luminescence quantum yields approaching unity (Φlum = 0.96–0.99) in the green region of the visible spectrum (534–554 nm) in diluted degassed dichloromethane solution. Similarly to other N^C^N platinum(II) complexes, a broad emission band grows in the deep red region (738–752 nm) upon increasing the concentration, due to the creation of bi-molecular emissive excited states. Interestingly, it appears that the introduction of a 2-thienyl group on the pyridine rings is a route to maintain excellent quantum yields even in concentrated solution. In order to have an insight into the electronic properties of the novel compounds, density functional theory (DFT) and time-dependent (TD)DFT approaches were employed to calculate the molecular geometry, the ground state, the electronic structure and the excited electronic states of the complexes, both as a monomers and dimers in solution.