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π-Conjugated chiral nanorings with intriguing electronic structures and chiroptical properties have attracted considerable interests in synthetic chemistry and materials science. We present the design principles to access new chiral macrocycles (1 and 2) that are essentially built on the key components of main-group electron-donating carbazolyl moieties or the π-expanded aza[7]helicenes. Both macrocycles show the unique molecular conformations with a (quasi) figure-of-eight topology as a result of the conjugation patterns of 2,2',7,7'-spirobifluorenyl in 1 and triarylamine-coupled aza[7]helicene-based building blocks in 2. This electronic nature of redox-active, carbazole-rich backbones enabled these macrocycles to be readily oxidized chemically and electrochemically, leading to the sequential production of a series of positively charged polycationic open-shell cyclophanes. Their redox-dependent electronic states of the resulting multispin polyradicals have been characterized by VT-ESR, UV-vis-NIR absorption and spectroelectrochemical measurements. The singlet (ΔES-T = -1.29 kcal mol-1) and a nearly degenerate singlet-triplet ground state (ΔES-T(calcd) = -0.15 kcal mol-1 and ΔES-T(exp) = 0.01 kcal mol-1) were proved for diradical dications 12+2• and 22+2•, respectively. Our work provides an experimental proof for the construction of electron-donating new chiral nanorings, and more importantly for highly charged polyradicals with potential applications in chirospintronics and organic conductors.

We herein describe the synthesis of a new class of axially chiral aza/boracyclophanes (BDN1, BXN1, BDB1 and BXB1) using binaphthyls as chiral building blocks and the main-group (B/N) chemistry with tunable electronic effects. All macrocycles substituted with triarylamine donors or triarylborane acceptors are strongly luminescent. These macrocycles showed two distinct meta and para π-conjugation pathways, leading to the formation of quasi figure-of-eight and square-shaped conformations. Interestingly, comparison of such structural models revealed that the former type of macrocycles BXN1 and BXB1 gave higher racemization barriers relative to the other ones. The results reported here may provide a new approach to engineer the optical stability of π-conjugated chiral macrocycles by controlling π-substitution patterns. The ring constraints induced by macrocyclization were also demonstrated to contribute to the configurational persistence as compared with the open-chain analogues p-BTT and m-BTT.

Supramolecular chemistry has received much attention for decades. Macrocyclic architectures as representative receptors play a vital role in supramolecular chemistry and are applied in many fields such as supramolecular assembly and host‐guest recognition. However, the classical macrocycles generally lack functional groups in the scaffolds, which limit their further applications, especially in optoelectronic materials. Therefore, developing a new design principle is not only essential to better understand macrocyclic chemistry and the supramolecular behaviors, but also further expand their applications in many research fields. In recent years, the doping compounds with main‐group heteroatoms (B, N, S, O, P) into the carbon‐based π‐conjugated macrocycles offered a new strategy to build macrocyclic architectures with unique optoelectronic properties. In particular, the energy gaps and redox behavior can be effectively tuned by incorporating heteroatoms into the macrocyclic scaffolds. In this Minireview, we briefly summarize the design and synthesis of new macrocycles, and further discuss the related applications in optoelectronic materials and supramolecular chemistry. [ABSTRACT FROM AUTHOR]

We herein present the synthetic approach to a new antiaromatic double aza[7]helicene C that features NN‐embedded polycyclic aromatic hydrocarbons (PAHs). This heteroatom‐doped helicene showed a rarely obtained long‐wavelength emission and far‐red circularly polarized luminescence (CPL) in the solid state. These optical and chiroptical properties could be ascribed to both the NN‐PAH core structure and the further extension through angular ring fusions. Such a unique electronic structure also culminated in facile chemical oxidations of neutral C to the positively charged chiral radical (C⋅+) and dication species (C2+). Interestingly, DFT computations revealed that the pyridazine central core showed an antiaromaticity‐to‐aromaticity switching, in contrast to the inversed transition for the helical periphery in cationic states. The reported approaches are anticipated to lead to the development of further redox‐active chiral systems for potential applications in chiroptoelectronics, spintronics as well as fluorescent bioimaging. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) from linear two‐coordinate coinage metal complexes is sensitive to the geometric arrangement of the ligands. Herein we realize the tuning of configuration from coplanar to orthogonal gradually by variation of substituents. In a complex with confined twist configuration, its blue emission peaking at 458 nm presents a high ΦPL of 0.74 and a short τTADF of 1.9 μs, which indicates a fast enough kr,TADF of 3.9×105 s−1 and a depressed knr of 1.4×105 s−1. Such outstanding luminescent properties are attributed to the proper overlap of HOMO and LUMO on CuId orbitals that guarantees not only small ΔEST but also sufficient transition oscillator strength for fast kr,S1 ${{k}_{{\rm r},{{\rm S}}_{1}}}$. Vacuum‐deposited blue OLEDs with either doped or host‐free emissive layer present external quantum efficiencies over 20 % and 10 %, respectively, demonstrating the practicality of the configurationally confined strategy for efficient linear CuI TADF emitters. [ABSTRACT FROM AUTHOR]

We herein describe a new design principle to achieve B/N‐doped cyclophane where an electron‐donor block of three triarylamines (Ar3N) and an acceptor block of three triarylboranes (Ar3B) are spatially separated on opposite sides of the π‐extended ring system. DFT computations revealed the distinct electronic structure of the block‐type macrocycle MC‐b‐B3N3 with a greatly enhanced dipole moment and reduced HOMO–LUMO energy gap in comparison to its analogue with alternating B and N sites, MC‐alt‐B3N3. The unique arrangement of borane acceptor Ar3B and amine donor Ar3N components in MC‐b‐B3N3 induces exceptionally strong intramolecular charge transfer in the excited state, which is reflected in a largely red‐shifted luminescence at 612 nm in solution. The respective linear open‐chain oligomer L‐b‐B3N3 was also synthesized for comparison. Our new approach to donor–acceptor macrocycles offers important fundamental insights and opens up a new avenue to unique optoelectronic materials. [ABSTRACT FROM AUTHOR]

Constructing chiral luminescent systems with both large luminescence dissymmetry factor (glum) and high luminous efficiency has been considered a great challenge. We herein describe a highly efficient approach to sterically stabilize the helical configurations of carbo[5]helicenes for improved CPL properties in a series of π-donor and π-acceptor substituted [5]helicenes (1, 2, 3, 4 and 5). Enabled by the ortho-installation of methyl groups as well as the steric effects of triarylamine (Ar3N) and triarylborane (Ar3B) handles in meta-substituted [5]helicenes, their optical resolution into enantiomers has been accomplished using preparative chiral HPLC. The molecular chirality of [5]helicenes can be transferred to Ar3B and Ar3N as light emitters, which allowed further investigations of their chiroptics, including optical rotation, circular dichroism (CD) and circularly polarized luminescence (CPL). Remarkably, 4 has been demonstrated to display dramatically enhanced CPL performance with a much larger glum (>1.2 × 10−2) and an increased emission quantum efficiency (ΦS = 0.75) compared with the other analogues, as a result of the isomeric tuning of substitutions with differential steric and electronic effects. These experimentally observed CPL activities were rationalized by TD-DFT computations for the angle (μ,m) between electric and magnetic transition dipole moments in the excited states. In addition, the conspicuous intramolecular donor–acceptor charge transfer led to thermal responses in the emissions of 2 and 4 over a broad temperature range. [ABSTRACT FROM AUTHOR]