Polycationic Open‐Shell Cyclophanes: Synthesis of Electron‐Rich Chiral Macrocycles, and Redox‐Dependent Electronic States

Abstract

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.

Hybridized Local and Charge Transfer Modulated Triplet Decay Brightens Ultra-Long Circularly Polarized Afterglow and Chiral Diradical Activity

“…The diradical character y0 of [(S)-PO2] 2•2+ is calculated to be 0.953 by Yamaguchi's scheme at the same UB3LYP−D3/6−31G(d) level (details see SI), which surpasses the previous TPA-based chiral diradicals (y0 = 0.53, 0.64). 56,73 Besides, the VT-ESR experiment is executed to unveil the spin ground state in [(S)-PO2] 2•2+ [(SbF6)2] 2− . The IT intensities gradually decrease with decreasing temperature from 160 to 95 K, corroborating a singlet ground state of these diradicals (Figure 5g).…”

Circularly Polarized Luminescent π‐Conjugated Chiral Nanorings and Nanobelts

“…52a). [69] The enantiomers of 123 and 124 were successfully separated through chiral HPLC. 124 has been demonstrated a high emission quantum efficiency of up to 0.99, and the B CPL = 100.2 M −1 cm −1 was calculated, which is the among the highest values reported for organic chiral macrocycles.…”

“…d) In situ UV/Vis-NIR spectra monitored by spectroelectrochemical measurements in CH 2 Cl 2 upon the oxidation of 123 at increased scan potentials (0-2.5 V). Reproduced with permission [69]. Copyright 2024, Wiley-VCH GmbH, Weinheim.…”