Weakly fluorescent (Z)-4-arylidene-5-(4H)-oxazolones (1), ΦPL < 0.1%, containing a variety of conjugated aromatic fragments and/or charged arylidene moieties, have been orthopalladated by reaction with Pd­(OAc)2. The resulting dinuclear complexes (2) have the oxazolone ligands bonded as a C^N-chelate, restricting intramolecular motions involving the oxazolone. From 2, a variety of mononuclear derivatives, such as [Pd­(C^N-oxazolone)­(O2CCF3)­(py)] (3), [Pd­(C^N-oxazolone)­(py)2]­(ClO4) (4), [Pd­(C^N-oxazolone)­(Cl)­(py)] (5), and [Pd­(C^N-oxazolone)­(X)­(NHC)] (6, 7), have been prepared and fully characterized. Most of complexes 3–6 are strongly fluorescent in solution in the range of wavelengths from green to yellow, with values of ΦPL up to 28% (4h), which are among the highest values of quantum yield ever reported for organometallic Pd complexes with bidentate ligands. This means that the introduction of the Pd in the oxazolone scaffold produces in some cases an amplification of the fluorescence of several orders of magnitude from the free ligand 1 to complexes 3–6. Systematic variations of the substituents of the oxazolones and the ancillary ligands show that the wavelength of emission is tuned by the nature of the oxazolone, while the quantum yield is deeply influenced by the change of ligands. TD-DFT studies of complexes 3–6 show a direct correlation between the participation of the Pd orbitals in the HOMO and the loss of emission through non-radiative pathways. This model allows the understanding of the amplification of the fluorescence and the future rational design of new organopalladium systems with improved properties.

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Cationic [Cu­(P^P)­(Htbz)]­PF6 [P^P = xantphos, dpephos; Htbz = 2-(4-thiazolyl)­benzimidazole] and the corresponding neutral complexes [Cu­(P^P)­(tbz)], obtained through deprotonation of the diimine ligand, have been synthesized with the aim of analyzing the role of the diphosphane and Htbz deprotonation in the emissive properties of these complexes. For the study of the diphosphane effect, the luminescence properties of these compounds have been compared with those of the reported analogous derivatives with Htbz and carborane diphosphanes. Complexes [Cu­(P^P)­(Htbz)]­PF6 (P^P = xantphos, dpephos) and [Cu­(dpephos)­(tbz)] display thermally activated delayed fluorescence, which has been studied, revealing a ΔE(S1–T1) between 658 and 455 cm–1. Theoretical calculations indicate different origins for the absorptions, leading to the observed emissions.