Intermolecular energy transfer processes typically involve an exothermic transfer of energy from a donor site to a molecule with a substantially lower-energy excited state (trap). Here, we demonstrate that an endothermic energy transfer from a molecular organic host (donor) to an organometallic phosphor (trap) can lead to highly efficient blue electroluminescence. This demonstration of endothermic transfer employs iridium(III)bis(4,6-di-fluorophenyl)-pyridinato-N,C2′)picolinate as the phosphor. Due to the comparable energy of the phosphor triplet state relative to that of the 4,4′-N,N′-dicarbazole-biphenyl conductive host molecule into which it is doped, the rapid exothermic transfer of energy from phosphor to host, and subsequent slow endothermic transfer from host back to phosphor, is clearly observed. Using this unique triplet energy transfer process, we force emission from the higher-energy, blue triplet state of the phosphor (peak wavelength of 470 nm), obtaining a very high maximum organic light-emitting device external quantum efficiency of (5.7±0.3)% and a luminous power efficiency of (6.3±0.3)lm/W.

Organic-inorganic hybrid metal halide perovskites have emerged as a highly promising class of light emitters, which can be used as phosphors for optically pumped white light-emitting diodes (WLEDs). By controlling the structural dimensionality, metal halide perovskites can exhibit tunable narrow and broadband emissions from the free-exciton and self-trapped excited states, respectively. Here, we report a highly efficient broadband yellow light emitter based on zero-dimensional tin mixed-halide perovskite (CNHBr)SnBrI (x = 3). This rare-earth-free ionically bonded crystalline material possesses a perfect host-dopant structure, in which the light-emitting metal halide species (SnBrI, x = 3) are completely isolated from each other and embedded in the wide band gap organic matrix composed of CNHBr. The strongly Stokes-shifted broadband yellow emission that peaked at 582 nm from this phosphor, which is a result of excited state structural reorganization, has an extremely large full width at half-maximum of 126 nm and a high photoluminescence quantum efficiency of ∼85% at room temperature. UV-pumped WLEDs fabricated using this yellow emitter together with a commercial europium-doped barium magnesium aluminate blue phosphor (BaMgAlO:Eu) can exhibit high color rendering indexes of up to 85.

No abstract

Generating sustainable fuel from sunlight plays an important role in meeting the energy demands of the modern age. Here we report the synthesis of new two-coordinate, molecular Cu(I) and Au(I) complexes that were designed to absorb visible photons (vis > 103 M-1cm-1), maintain long excited state lifetimes (~1-0.1s), and perform stable photo-induced charge transfer to a target substrate with remarkably potent photoreducing capabilities (E+/* up to 2.33 V vs. Fc+/0). The photoredox performance was evaluated in a variety of solvents, and we were able to understand the influence of ligand design and metal center on the photophysical properties. Interestingly, we found that the Cu(I) systems have competitive figures of merit with widely used scarce metal photosensitizers such as Ru(bpy)32+ and Ir(ppy)3. This work illuminates two-coordinate coinage metal complexes as promising, abundant metal, solar fuels photosensitizers that offer exceptional tunability and photoredox properties.