Organic heterojunctions are widely used in organic electronics and they are composed of semiconductors interfaced together. Good ordering in the molecular packing inside the heterojunctions is highly desired but it is still challenging to interface organic single crystals to form single-crystalline heterojunctions. Here, we describe how organic heterojunctions are formed by interfacing two single crystals from a droplet of a mixed solution containing two semiconductors. Based on crystallization of six organic semiconductors from a droplet on a substrate, two distinct crystallization mechanisms have been recognized in the sense that crystals form at either the top interface between the air and solution or the bottom interface between the substrate and solution. The preference for one interface rather than the other depends on the semiconductor–substrate pair and, for a given semiconductor, it can be switched by changing the substrate, suggesting that the preference is associated with the semiconductor–substrate molecular interaction. Furthermore, simultaneous crystallization of two semiconductors at two different interfaces to reduce their mutual disturbance results in the formation of bilayer single crystals interfaced together for organic heterojunctions. These single-crystalline heterojunctions exhibit ambipolar charge transport in field-effect transistors, with the highest electron mobility of 1.90 cm2 V–1 s–1 and the highest hole mobility of 1.02 cm2 V–1 s–1. Hence, by elucidating the interfacial crystallization events, this work should greatly harvest the solution-grown organic single-crystalline heterojunctions.

emerging as an enabling technology. [1][2][3][4] The combination of flexibility and responsiveness allows applications in various fields, including wearable electronics, soft robotics, drug delivery, biomedical devices, and biomimetic design. [5][6][7][8][9][10] Among various material options, polymers play an essential role in fabricating flexible sensors and soft actuators due to their tailorability and the potential of integrating multiple functionalities, such as adaptive response to signals (e.g., chemical, mechanical, electrical), energy harvesting and storage, and biochemical sensing. [3,10] Adding responsive functionality to a polymer often involves methods such as copolymerizing monomers with different capability, attaching layers of active materials to a polymer matrix, building in molecular orientation or internal polarization, introducing structural heterogeneity by combining amorphous and crystalline domain or multi-layer assembly, and preparing composites by hybridizing organic and inorganic materials. [2,[11][12][13][14] Among various techniques, utilizing dynamic chemistry to enable polymer responsivity has received significant attention in the past few decades. [15,16] Reversible interactions, including dynamic covalent bonding, hydrogen bonding, ionic bonding, π-π stacking, and metal-ligand coordination, are susceptible to environmental variation and can achieve multiple physical and chemical responses via bond breaking and reforming. [17][18][19][20][21] Fascinating material properties arise from disrupting the equilibrium state of dynamic bonding, for example: polymers with spiropyran go through force-induced covalent-bond activation and give rise to visible color and fluorescence; supramolecular polymers containing metal-ligand motifs can self-heal by exposing to ultraviolet irradiation; and polymers functionalized by self-complementary hydrogen bonded ureidopyrimidinone (UPy) moieties shows shape-memory effect through temperature change. [22][23][24] Among these options, metal-ligand coordination bonding is particularly appealing to realize a particular desired response, because of the ease of tuning the stability of the bond.One of the most popular polymers for fabricating sensors and actuators is polydimethylsiloxane (PDMS). [2,7] It commonly serves as an essential substrate or a responsive component due to the attractive physical and chemical properties, including low Polymers are at the core of emerging flexible sensor and soft actuator technology. Ideal candidates not only respond to external stimuli but also have programmable response intensity and speed. Incorporating dynamic interactions into polymers has been widely studied. However, most research has focused on synthesis methods and on optical and mechanical effects of these interactions. Here, a new and tunable method of enabling environmentally adaptive polymers are introduced. Specifically, polar functionalities are "hidden" within polydimethylsiloxane (PDMS). When unveiled, these polar functionalities change the hydrophilicity ...

The separation of C8 aromatics (xylenes and ethylbenzene) remains one of the most challenging industrial separations due to their similar structures and properties. Suitable adsorbents that can distinguish the small differences among isomers are urgently demanded. Herein, we demonstrate a strategy to realize the precise discrimination of C8 aromatics by constructing a nonaromatic confined pore environment with mixed polycycloalkane-type ligands. The nonaromatic low-polar pore environment avoids strong convergent interactions between the framework and the common phenyl rings while creating possibilities to amplify the difference between host–guest/guest–guest interactions regarding the different methyl (ethyl) group positions of isomers. The resultant metal–organic framework, ZUL-C3, with either tetragonal or monoclinic lattice, exhibits outstanding separation performance for C8 aromatics, not only realizing the simultaneous separation of four isomers from each other but also setting a benchmark for the dynamic separation performance of OX/PX and OX/MX.

Dynamic bonds are a powerful approach to tailor the mechanical properties of elastomers and introduce shape-memory, self-healing, and recyclability. Among the library of dynamic crosslinks, electrostatic interactions among oppositely charged...

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