Organic fluorophores with reversible emission switching behavior are promising materials for applications in sensors, optical recording, security inks, and optoelectronics. A variety of aggregation-induced emission (AIE) luminogens with mechanochromic luminescence has been prepared, and the transformation of efficient bluer-emitting crystals to amorphous powders with redder and weaker emission is proposed to be the cause for such behavior. However, detailed mechanistic understanding from experimental to theoretical is lacking. In this work, we present the design and synthesis of a group of bis­(diarylmethylene)­dihydroanthracenes with butterfly-like shapes. These molecules exhibit aggregation-induced emission characteristics due to the restriction of intramolecular motion in the aggregated state. They show mechanochromism, because of the transformation between crystal and amorphous states with different colors and efficiencies aided by grinding/heating or solvent fuming processes. By investigation of their single-crystal structures and theoretical calculations, the loose molecular packing with noncovalent intermolecular interactions, the extent of conformational twisting, and the packing density of the luminogens, as well as freedom of intermolecular motion in the excited state, are stemmed for their reversible polymorphism-dependent emission behaviors.

wileyonlinelibrary.com COMMUNICATIONreported mechanochromic luminescent materials contain a single luminophore with two fl uorescent states, and thus their fl uorescence can be switched between two colors or two different intensities. [ 5a , 6 ] However, examples exhibiting mechanochromic phosphorescence are rather rarely seen in literature, except for a few metal complexes showing mechanochromic phosphorescence with short lifetimes. [ 7 ] It is known that room temperature phosphorescent (RTP) emissions often occur in metal complexes, but rare for pure organic luminogens. [ 8 ] The development of organic mechanochromic phosphorescence is of great importance from both a scientifi c and a practical point of view.Our group has observed RTP in organic crystals of nonplanar molecules containing carbonyl groups, while phosphorescence is absent in the corresponding amorphous aggregates. This phenomenon has been attributed to crystallization-induced phosphorescence (CIP). [ 9 ] Inspired if mechanochromic or thermochromic phosphorescence can be achieved by means of reversible morphology transformation between the crystalline and amorphous states of those luminescent organic materials. Unfortunately, quick crystallization of those RTP luminogens makes it diffi cult to obtain their amorphous aggregates by mechanical stimulus or thermal method. Therefore, to achieve mechanochromic phosphorescence, it is desirable to attenuate the crystallization ability of those luminegens, which can be realized through a suitable molecular design.In this paper, we present the unique photoluminescent (PL) properties of solid materials based on luminogen 1 ( Figure 1 ), where carbazolyl groups are introduced at the p -positions of phenyl rings in benzophenone molecule. In the molecular crystals of luminogen 1 , the fl uorescent processes can be significantly inhibited with the assistance of chloroform (TCM). However, luminogen 1 exhibiting RTP with ultralong lifetime and the RTP decay process is observable even with the naked eyes, which is unusual for organic luminogens. Remarkably, the persistent RTP of 1 can be repeatedly switched on and off facilely by repeating the fuming-heating or fuming-grinding process. Meanwhile, when phosphorescence was shut down, the solid materials can exhibit multiple fl orescent states depending on the morphologies. The different fl uorescent states can be reversibly switched between each other when vapor, thermal, and mechanical stimuli were applied. Owing to the versatile

Lead (Pb) and cadmium (Cd) are highly toxic and are widespread in agricultural soils, representing risks to plant and human health. In this study, Davidia involucrata was cultivated in soil with different concentrations of Pb and Cd and sampled after 90 days. We used ANOVA to analyse the photosynthesis of D. involucrata and the ability of Pb and Cd to enrich and migrate in roots, stems and leaves. Various results are described here. 1) Under individual and combined Pb and Cd stress, the accumulation factors in the roots were greater than 1, which was significantly greater than those in the stems and leaves (P < 0.05), and the translocation factors both were less than 1. The Pb and Cd enrichment ability of D. involucrata roots was significantly higher than that of stems and leaves, and the migration ability of the two heavy metals in D. involucrata was weak. 2) The Mg-dechelatase activities of chlorophyll degradation products increased under stress due to high concentrations of Pb and Cd. However, chlorophyllase activity was higher at relatively low concentrations of the two heavy metals (P < 0.05). δ-Aminolevulinic acid and porphobilinogen of chlorophyll synthesis products are easily converted to uroporphyrinogen III under low concentrations of Cd, which promotes the synthesis of chlorophyll.3) The effect of Cd stress alone on the chlorophyll concentration was not significant. Under combined stress, concentrations of Pb and Cd in the range of 400~800 mg�kg -1 and 5~20 mg�kg -1 significantly promoted an increase in photosynthetic pigments (P < 0.05). 4) Inhibition of the net photosynthetic rate increased with increasing Pb and Cd concentrations under both individual and combined stress. In addition, the root of D. involucrata had a strong absorption and fixation effect on heavy metals, thereby reducing metal toxicity and improving the tolerance of D. involucrata to heavy metals. , et al. (2020) Response of photosynthesis to different concentrations of heavy metals in Davidia involucrata. PLoS ONE 15(3): e0228563.

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