A conjugated <i>β</i>-triketone, tris(2-naphthoyl)methane (<b>tnm</b>H), has been synthesized and successfully utilized as an antenna moiety for sensitization of the trivalent lanthanoids Eu³⁺_,Sm³⁺_,Yb³⁺and Nd³⁺, in an isomorphous series of mononuclear complexes formulated as [Ln(<b>tnm</b>)₃(DMSO)₂] (Ln³⁺= Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺and Yb³⁺). The photophysical properties of the materials were characterized as comprehensively as possible, with overall quantum yields, intrinsic quantum yields based on calculated radiative decays, and sensitization efficiencies reported. This investigation improves understanding of the sensitization processes occurring in the near-infrared (NIR) region systems in particular, where quantitative data is currently scarce. In fact, the [Yb(<b>tnm</b>)₃(DMSO)₂] and its deuterated analogue, [Yb(<b>tnm</b>)₃(<i>d₆-</i>DMSO)₂], present high values of overall quantum yield of 4% and 6%, respectively, which makes them useful and readily accessible references for future investigation of NIR-emitting systems.

<div><div><div><p>The tetrazole-functionalised calixdiquinone 5,17-di-tert-butyl-26,28-bis-(tetrazol-5-ylmethoxy)- calix[4]-25,27-diquinone Q was synthesised by chemical oxidation of the bis-tetrazole calix[4]arene precursor using PbO2/HClO4. The single crystal X-ray structure determination of Q confirmed the structure and showed binding of a water molecule in the solid state. Chemical reduction of Q to the dihydroquinone QR was achieved using N,N-diethylhydroxylamine. Comparison of the solution phase photophysical properties of Q or QR in the presence of terbium ions showed significant excitation only with QR, suggesting redox switching of the photophysical response may be possible with this or similar receptors.</p></div></div></div>