White luminescence achieved by a multiple thermochromic emission in a hybrid organic-inorganic compound based on 3-picolylamine and copper(I) iodide

Three copper(I) complexes have been obtained by the reaction of CuI with 3-picolylamine in acetonitrile solution and characterized by X-ray powder diffraction, both from synchrotron and laboratory radiation. Photophysical investigations in the solid state revealed highly efficient thermally-activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) up to 18%. Notably, the complex [Cu2I2(3pica)](infinity) displays a strong luminescence thermochromism due to the presence of both (1,3)(X + M) LCT excited states and a lower-lying cluster-centered ((CC)-C-3) one, leading to multiple emission at room temperature; as a result, a white luminescence is achieved with a PLQY of 4.5%.