Efficient electronic coupling is the key to constructing optoelectronic functional π systems. Generally, the delocalization of π electrons must comply with the framework constructed by covalent bonds (typically σ bonds), representing classic through-bond conjugation. However, through-space conjugation offers an alternative that achieves spatial electron communication with closely stacked π systems instead of covalent bonds thus enabling multidimensional energy and charge transport. Because of the ever-accelerating advances of through-space conjugation studies, researchers are inspired greatly by the beauty of through-space conjugated systems and their potential in high-tech applications. In this mini review, we introduce some representative and newly developed π systems having the through-space conjugation feature. In addition to discussing the profound impacts of through-space conjugation on the luminescence properties and charge transport, we will review some impressive findings of distinctive molecules with attractive characteristics, such as aggregation-induced emission, thermally activated delayed fluorescence, bipolar charge transport, and multichannel. These achievements may bring about new breakthroughs of theory, materials, and devices in the fields of organic electronics and molecular electronics.

Molecular potentiometers that can indicate displacement-conductance relationship, and predict and control molecular conductance are of significant importance but rarely developed. Herein, single-molecule potentiometers are designed based on ortho-pentaphenylene. The ortho-pentaphenylene derivatives with anchoring groups adopt multiple folded conformers and undergo conformational interconversion in solutions. Solvent-sensitive multiple conductance originating from different conformers is recorded by scanning tunneling microscopy break junction technique. These pseudo-elastic folded molecules can be stretched and compressed by mechanical force along with a variable conductance by up to two orders of magnitude, providing an impressively higher switching factor (114) than the reported values (ca. 1~25). The multichannel conductance governed by through-space and through-bond conducting pathways is rationalized as the charge transport mechanism for the folded ortho-pentaphenylene derivatives. These findings shed light on exploring robust single-molecule potentiometers based on helical structures, and are conducive to fundamental understanding of charge transport in higher-order helical molecules.

Constructing single‐molecule parallel circuits with multiple conduction channels is an effective strategy to improve the conductance of a single molecular junction, but rarely reported. We present a novel through‐space conjugated single‐molecule parallel circuit (f‐4Ph‐4SMe) comprised of a pair of closely parallelly aligned p‐quaterphenyl chains tethered by a vinyl bridge and end‐capped with four SMe anchoring groups. Scanning‐tunneling‐microscopy‐based break junction (STM‐BJ) and transmission calculations demonstrate that f‐4Ph‐4SMe holds multiple conductance states owing to different contact configurations. When four SMe groups are in contact with two electrodes at the same time, the through‐bond and through‐space conduction channels work synergistically, resulting in a conductance much larger than those of analogous molecules with two SMe groups or the sum of two p‐quaterphenyl chains. The system is an ideal model for understanding electron transport through parallel π‐stacked molecular systems and may serve as a key component for integrated molecular circuits with controllable conductance.

Intramolecular charge transfer (ICT) has significant impacts on organic optoelectronic materials, photochemistry, biotechnology, and so on. However, it is hard to stabilize the ICT state because of the rapid nonradiative charge recombination process, which often quenches light emission. In this work, we use new foldamers of the protonated pyridine-modified tetraphenylethene derivatives that possess through-space conjugation (TSC) characters as the models to study the impact of TSC on the ICT state. Steady and transient spectroscopies illustrate that the lifetime of the ICT state in the molecule with strong TSC can be much longer than those of molecules without TSC, giving rise to a higher fluorescence quantum yield. By combining the theoretical calculations, we demonstrate that the strong TSC can stabilize the ICT state and slow the charge recombination rate by more efficiently dispersing charges. This is a conceptually new design strategy for functional optoelectronic materials that require more stable ICT states.

Blue luminescent materials are always highly desired for organic light‐emitting diodes (OLEDs) but the electroluminescence (EL) performances for most blue emitters still need to be improved in both efficiency and stability. In this work, four bipolar molecules with twisted donor‐acceptor structures (PIPD‐MP‐DPA, PIPD‐MP‐IMDB, PIPD‐MP‐DMAC, and PIPD‐MP‐DPAC) are designed and synthesized. These molecules possess good thermal and electrochemical stabilities, and exhibit strong deep‐blue photoluminescence. Their non‐doped OLEDs show deep‐blue EL emissions at 418–438 nm, and high maximum external quantum efficiencies (ηext,max) of up to 4.4% with a CIEy value of only 0.078. Furthermore, the phosphorescent OLEDs (PhOLEDs) based on PIPD‐MP‐DPA host achieve excellent ηext,max of 25.9% and 28.0% for green and orange, respectively, with small efficiency roll‐offs. In addition, PIPD‐MP‐DPA is also employed to construct hybrid white OLEDs (WOLEDs), giving high ηext,max of 21.6% for two‐color WOLEDs, and 16.3% for four‐color WOLEDs. In brief, these bipolar materials reveal outstanding EL performances in deep‐blue fluorescent, phosphorescent, and hybrid white OLEDs, indicating huge potential applications in display and lighting techniques.

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The construction of multivalued logic circuits by multiple quantum-interfered states at the molecular level can make full use of molecular diversity and versatility, broadening the application of molecular electronics. Understanding charge transport through different conducting pathways and how they interact with each other in molecules with a secondary structure is an indispensable foundation to achieve this goal. Herein, we elucidate the synergistic effect from through-space and through-bond conducting pathways in foldamers derived from ortho-pentaphenylene by the separate modulation on these pathways. The shrinkage of central heterocycles’ sizes allows foldamers to stack with larger overlap degrees, resulting in level-crossing and thus transformation from constructive quantum interference (CQI) to destructive quantum interference (DQI) in a through-space pathway. The alteration of central heterocycles’ connection sites enhances through-bond conjugation, leading to amplified contribution from a through-bond pathway. The enhanced through-bond pathway destructively interferes with the through-space pathway, exerting a suppression effect on transmission. Therefore, four quantum-interfered states of through-space and through-bond combination are generated, including through-space CQI-dominated states, through-space DQI-dominated states, through-space CQI states with through-bond suppression, and through-space DQI states with through-bond suppression. These findings enable us to regulate charge transport within high-order structures via multiple conducting pathways and provide a proof of concept to construct multivalued logic circuits.

The coal fires, a global catastrophe for hundreds of years, have been proved extremely difficult to control, and hit almost every coal-bearing area globally. Meanwhile, underground coal fires contain tremendous reservoir of geothermal energy. Approximately one billion tons of coal burns underground annually in the world, which could generate ~1000 GW per annum. A game-changing approach, environmentally sound thermal energy extraction from the intractable natural coalfield fires, is being developed by utilizing the waste energy and reducing the temperature of coalfield fires at the same time. Based on the Seebeck effect of thermoelectric materials, the temperature difference between the heat medium and cooling medium was employed to directly convert thermal energy into clean electrical energy. By the time of December 2016, the power generation from a single borehole at Daquan Lake fire district in Xinjiang has been exceeded 174.6 W. The field trial demonstrates that it is possible to exploit and utilize the waste heat resources in the treated coal fire areas. It promises a significant impact on the structure of global energy generation and can also promote progress in thermoelectric conversion materials, geothermal exploration, underground coal fires control and other energy related areas.