Precise Regulation of Distance between Associated Pyrene Units and Control of Emission Energy and Kinetics in Solid State

Many approaches have been explored to tune emission behaviors of organic luminogens. However, precise regulation of distances in dimers is seldom reported. Here, four pyrene derivatives are presented, and we precisely regulate the distance between pyrene units of X2P. Its crystal manifests unusual deep-blue excimer emission at 424 nm, while the crystal of X1P with only one pyrene unit for each molecule gives sky-blue emission with a maximum emission peak at 475 nm, which even shows an unexpected bathochromic shift effect compared with the emission of the needle crystal of X2EP with the largest conjugated structure and tunable tristate kinetics of excimer emissions upon different stimuli. Notably, the excimer decay time of the X2P crystal (26.4 ns) is apparently shorter than that of the X1P crystal (106.0 ns). The qualitative and quantitative analysis of π–π interactions with different distances between pyrene units in crystals was performed for the first time, leading to the conclusion that short distance and strong π–π interactions are vital to lower excited-state energy and weaken delayed fluorescence. This study introduces an easy and efficient way to precisely regulate distances in dimer and control the emission energy and kinetics of the decay process in the solid state for unique applications, as well as to predict the distance based on emission wavelength.