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.

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The study of the transformation of heavy metals during the coal combustion process is of great significance to controlling their emission. In this study, three coals with different contents of arsenic (As), lead (Pb), and mineral elements were selected. The experiments were conducted at 900−1300 °C using a drop tube furnace system. The transformation of As and Pb during the combustion processes of the three coals was obtained. It was found that both the gaseous and particulate phases were important forms of As and Pb in the combustion products. As the temperature increased, the proportion of gaseous-phase As of the YBS (Yuan Baoshan) coal and JT (Jing Tai) coal first increased and then decreased, and the proportion of gaseous-phase As of the HLH (Huo Linhe) coal increased slightly. As the temperature increased, the proportion of gaseousphase Pb of the three coals increased and reached approximately 65% at 1300 °C. For the particulate phase, As and Pb were mainly present in ultramicrometer particles after combustion. The differences in the three coal components caused the different distributions of As and Pb in the gaseous and solid combustion products. The coal with a high content of iron (Fe) and calcium (Ca) was more conducive to the migration of gaseous-phase As to solid-phase As during flue gas cooling, while the effects of Ca and sulfur (S) on Pb transformation in the coal were offset. The original modes of occurrence of As and Pb in the three coals were mainly organic-bound and residual forms. During the combustion process, the organic-bound As and Pb were completely released, the residual As and Pb were partially released, and small amounts of water-soluble and ion-exchangeable As and Pb were formed. The analysis of the distribution characteristics of As and Pb in the combustion products showed that the direct release ratios of As and Pb during high-temperature combustion were greater than 45%. During flue gas cooling, more than 60% of As and Pb in the submicrometer particle were produced by transformation from the gaseous phase to particulate phase.

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