Naphthyl-Substituted Carbodiphosphoranes: Synthesis, Formation of Copper(I) Complexes, and Thermally Activated Delayed Fluorescence Properties

Abstract We present the two-step synthesis of two new 2-naphthyl-substituted carbodiphosphoranes (CDPs). In the first step, either two equivalents of P(Naph)Ph2 (Naph = 2-naphthyl) and CH2Br2 or P(Naph)Ph2 and [Ph3P(CH2Br)]Br are reacted, whereby the symmetrical bis(phosphonium) salt 1a and the unsymmetric salt 1b are obtained. Subsequently, the CDPs 2a and 2b were prepared by deprotonation with two equivalents of potassium bis(trimethylsilyl)amide. After isolation, the coordination chemistry of 2a and 2b toward CuCl is explored where, depending on the stoichiometries of the starting materials, mononuclear (3a and 3b) and dinuclear compounds (4a and 4b) are obtained. All prepared compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis, and for 1a/b, 2a, 3b, and 4a/b, single crystals suitable for X-ray diffraction studies could be obtained. Furthermore, the photophysical properties of the 2-naphthyl-substituted CDPs 2a/b and their corresponding CuI complexes 3a/b and 4a/b have been investigated by steady-state and time-resolved luminescence studies at room temperature and at 77 K in various aggregation states, and further insight is provided by DFT/TD-DFT calculations. While 2a/b display features of thermally activated delayed fluorescence (TADF), 3a/b and 4a/b exhibit a much more complex excited-state behavior due to the interplay of metal-to-ligand charge transfer (MLCT) and naphthyl ligand-centered (LC) states, resulting in multiple simultaneous luminescence phenomena involving TADF, 1LC, and 3LC emission.