Room-Temperature Phosphorescence of Pure Axially Chiral Bicarbazoles

Abstract

Ultralong room-temperature phosphorescence (RTP) is greatly important in a series of applications, but obtaining RTP from metal-free organic materials is still an enormous challenge due to the spin-forbidden nature of triplet excitons. Because of its electron-rich nature and easy derivatization, carbazole (Cz) is widely used to build organic RTP and thermally activated delayed fluorescence (TADF) materials. However, Liu et al. (Nat. Mater. 2021, 20, 175) recently demonstrated that the RTP of Cz is induced by charge traps of its isomeric impurity in commercial sources. Here, on the basis of the classical El-Sayed rule and the recently discovered intersystem crossing promotion principles (twisted structure and charge transfer), we designed and prepared highly pure (>99.9%) (R/S)-octahydrobinaphthyl-based bicarbazoles (BiCz) for high-performance RTP (Φ P = 23%; τ p = 1.09 s). Interestingly, BiCz exhibited photoactivated TADF and RTP in isolated and aggregated states, respectively, and thus would be an efficient tool for rejuvenating Cz-based RTP.

“Point-Line-Plane-Helix” Binuclear Platinum(II) Complexes: Metal-Induced Chirality, Chirality Self-Sorting, and Chiroptical Properties

“…As depicted in Figures 3 and 4, the point and axial chiralities of the bridging ligands remain constant in the single crystals of (R,R,R,R p ,M)/ (S,S,S,S p ,P)-Me and (S,S,S,S p ,P)-iPr, revealing the fact that the point chirality and even axial chirality are stable enough to avoid racemization during the synthesis process. 29,30 As expected, not only molecular structures but also molecular arrangements of (R,R,R,R p ,M)/(S,S,S,S p ,P)-Me are mirrored, 24,25,31,32 because they are a pair of enantiomers (Figure 3a). As an example, (R,R,R,R p ,M)-Me is a two-layer-helix structure.…”

Circularly Polarized Luminescence Switching, Chirality Self‐Sorting, and Cell Imaging of Chiral Rhodamine Dyes

“…(R)/(S)-octahydro-BINOL (Commercially available, ee > 99%) were adopted as starting materials because their derivatives might have good solubility and high fluorescence quantum yields. [58,61] Under the same…”

“…[33][34][35][36][37][38] We always have focused on the synthesis and chiroptical properties of BINOL/BINAM derivatives. [53][54][55][56][57][58][59][60][61] In the present work, we utilize a simple and straightforward way to link two rhodamine chromophores by different chiral bridges. The conjugated (R,R,R)/(S,S,S) birhodamine dyes (1 and 2, Figure 1b) with one axial chirality and two spirocyclic chiralities in the middle and periphery of two rhodamine chromophores, respectively, show the interesting CD and CPL switching and lysosome-targetable properties.…”

Recent advances in room temperature phosphorescence of chiral organic materials

“…Indeed, scientists reinvestigate carbazole RTP systems and pay strong attention to the purity of the obtained compounds to fully elucidate the potential role of this side product on the intensity of the phosphorescence emission. In this context, Xiang et al have recently described a new pair of axially chiral bicarbazole derivatives, namely R / S ‐ BiCz (Figure 7), 77 based on the combination of the Cz core with an aromatic ketone used as ISC facilitator, and with a twisted binaphthyl skeleton for inducing the chirality property while limiting the conjugation between the two aromatic units. To ensure the absence of isomeric impurity found in commercial Cz sources, the preparation of the key building block was performed through a Pd‐catalyzed coupling reaction and the purity of the final targets was further confirmed by HPLC analyses after additional column chromatography and recrystallization.…”