Platinum Phosphors Containing an Aryl‐modified β‐Diketonate: Unusual Effect of Molecular Packing on Photo‐ and Electroluminescence

Abstract

AbstractThree new FPt1 [(2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′)(2,4‐pentanedionato‐ O,O)Pt(II)] analogues, Ph‐FPt, CzP‐FPt, and mCzP‐FPt, chelated with a 3‐aryl‐substituted acac ligand were synthesized. As shown by the results of X‐ray diffraction, the nearest neighboring molecules in the FPt1, Ph‐FPt, and CzP‐FPt crystals have a Pt–Pt distance of ~4.5, 4.5, and 7.0 Å, respectively. In contrast, in the mCzP‐FPt crystals, the nearest neighboring molecules exhibit a Pt–Pt distance of only 3.49 Å. All four Pt complexes show the same monomeric emission spectrum in dilute solution. However, in the crystalline state, mCzP‐FPt with a clear Pt–Pt bimetallic interaction shows only the low‐energy orange broadband emission; complexes FPt1, Ph‐FPt, and CzP‐FPt without significant Pt–Pt interaction (Pt–Pt distance > 4 Å) give higher‐energy emission closely resembling that of the monomeric species. The results provide clear evidence that the Pt–Pt bimetallic interaction is responsible for the low‐energy broadband emission of these Pt complexes. Unlike in the crystalline state, all of the four platinum complexes in the thin film give only the low‐energy broadband emissions with some difference in wavelength. In a similar manner, these platinum complexes‐based, non‐doped electroluminescence (EL) devices also emit only low‐energy orange broadband light. The non‐doped EL device using CzP‐FPt as the emitter showed a very promising external quantum efficiency of 10%, nearly five times higher than that of the FPt1 control device. The higher EL efficiency of the CzP‐FPt non‐doped device is mainly ascribed to the lower concentration of Pt–Pt dimers that effectively suppresses the self‐quenching between the orange emissive dimers.