Modular synthesis, host-guest complexation and solvation-controlled relaxation of nanohoops with donor-acceptor structures

Synthesis and Properties of a Strained Triple Nanohoop

A strained triple nanohoop with a shared central benzene unit is synthesized using a threefold intramolecular ring-closing approach. Among the five possible constitutional isomers, the isomer with the highest D3h symmetry is isolated, the structure of which contains three nanohoop blades and a central hexaphenylbenzene unit. The structure is elucidated using NMR spectroscopy and mass spectrometry. The optical and electrochemical properties are investigated, revealing a moderate fluorescence quantum yield of 40 %. A water-soluble nanomaterial is prepared using a nanoparticle encapsulation method, and a fluorescence quantum yield of 10 % is retained, which demonstrates the potential of the nanomaterial in biological systems.

Facile Synthesis of Donor-Acceptor Heterocycloarenes Based on Pyrazine Derivatives Possessing Intriguing Iodide Ion Capture Properties

Donor-acceptor (D-A) conjugated systems have been extensively investigated and play important roles in organic electronics. Incorporating D-A structures into (hetero)cycloarenes endows them tunable electronic properties, while the well-defined cavity remains. However, the synthetic complexity of introducing electron-acceptor moieties into (hetero)cycloarenes limits their development and applications. In this paper, the first family of electronically tunable D-A heterocycloarenes (DAHCn, n = 1-5) based on pyrazine derivatives was facilely synthesized through cyclocondensation reaction from a tetraketone-functionalized heterocycloarene precursor prepared using the ketal-protection strategy. The effect of expanded conjugation and the inserted electron-withdrawing group on the electronic structures of the D-A heterocycloarenes was studied systematically by X-ray crystallographic analysis, various spectroscopic measurements, and theoretical calculations. Interestingly, the presence of an electron-withdrawing group polarizes the inner C(sp2)-H and significantly increases the binding affinities of D-A heterocycloarenes to the iodide anion. Meanwhile, the anion affinity can be further modulated by the type of attached substituents and the distance of polarization. More importantly, the dicyanopyrazine derivative DAHC3 shows the highest binding strength to the iodide ion as a 2:1 sandwich complex (log β2 = 12.3 and ΔG = -69.1 kJ mol-1), which is the strongest iodide receptor using C(sp2)-H hydrogen bonding interactions reported to date. Our finding provides a new strategy to design and synthesize D-A heterocycloarenes and strong anion receptors.

Multi-heteroatom doped nanographenes: enhancing photosensitization capacity by forming an electron donor-acceptor architecture

Systematically tuning and optimizing the properties of synthetic nanographenes (NGs) is particularly important for NG applications in diverse areas. Herein, by devising novel electron donor-acceptor (D-A) type structures, we reported a series of multi-heteroatom-doped NGs possessing an electron-rich chalcogen and electron-deficient pyrimidine or pyrimidinium rings. Comprehensive experimental and theoretical investigations revealed significantly different physical, optical, and energetic properties compared to the non-doped HBC or chalcogen-doped, non-D-A analogues. Some intriguing properties of the new NGs such as unique electrostatically oriented molecular stacking, red-shifted optical spectra, solvatochromism, and enhanced triplet excitons were observed due to the formation of the D-A electron pattern. More importantly, these D-A type structures can serve as photosensitizers to generate efficiently reactive-oxygen species (ROS), and the structure-related photosensitization capacity that strengthens the electron transfer (ET) process leads to significantly enhanced ROS which was revealed by experimental and calculated studies. As a result, the cell-based photodynamic therapy (PDT) indicated that the cationic NG 1-Me+ is a robust photosensitizer with excellent water-solubility and biocompatibility.

Host-Guest Chemistry in Binary and Ternary Complexes Utilizing π-Conjugated Carbon Nanorings

The carbon nanorings, possessing a radial π system, have garnered significant attention primarily due to their size-dependent photophysical properties and the presence of a unique curved π-conjugated cavity. This is evidenced by the rapid proliferation of publications. Furthermore, the integration of building blocks into CPP skeletons can confer [n]CPPs with novel and exceptional photophysical and electronic characteristics, as well as chiral properties and host-guest interactions, thereby augmenting the diversity of [n]CPPs. Notably, the curved π surface structures and concave cavity of carbon nanorings enable them to host aromatic or non-aromatic guests with a complementarily curved surface, resulting in interesting binary or ternary complexes. This review provides a comprehensive treatment of literature reports on binary and ternary complexes, focusing on both their host-guest interactions and properties. It is important to note that the scope of this review is limited to host-guest chemistry in binary and ternary complexes based on π-conjugated carbon nanorings.

Appending Coronene Diimide with Carbon Nanohoops Allows for Rapid Intersystem Crossing in Neat Film

The development of innovative triplet materials plays a significant role in various applications. Although effective tuning of triplet formation by intersystem crossing (ISC) has been well established in solution, the modulation of ISC processes in the solid state remains a challenge due to the presence of other exciton decay channels through intermolecular interactions. The cyclic structure of cycloparaphenylenes (CPPs) offers a unique platform to tune the intermolecular packing, which leads to controllable exciton dynamics in the solid state. Herein, by integrating an electron deficient coronene diimide (CDI) unit into the CPP framework, a donor-acceptor type of conjugated macrocycle (CDI-CPP) featuring intramolecular charge-transfer (CT) interaction was designed and synthesized. Effective intermolecular CT interaction resulting from a slipped herringbone packing was confirmed by X-ray crystallography. Transient spectroscopy studies showed that CDI-CPP undergoes ISC in both solution and the film state, with triplet generation time constants of 4.5 ns and 238 ps, respectively. The rapid triplet formation through ISC in the film state can be ascribed to the cooperation between intra- and intermolecular charge-transfer interactions. Our results highlight that intermolecular CT interaction has a pronounced effect on the ISC process in the solid state, and shed light on the use of the characteristic structure of CPPs to manipulate intermolecular CT interactions.

Modulation of [8]CPP properties by bridging two phenylene units

We report the synthesis and characterization of two new fluorophores, consisting of a [8]cyclo-para-phenylene core in which two phenylenes are bridged by either a nitrogen atom or a carbonyl group. The nitrogen bridge increases the HOMO-LUMO gap, whereas the carbonyl bridge decreases it. These results provide guidelines to control the electronic properties of nanohoops.