Helical β‐isoindigo‐Based Chromophores with B−O−B Bridge: Facile Synthesis and Tunable Near‐Infrared Circularly Polarized Luminescence

Abstract

It is essential to create organic compounds that exhibit circularly polarized luminescence (CPL) in the near-infrared (NIR) range. Helicene-type emitters possess appealing chiroptical features, however, such NIR molecules are scarce due to a paucity of synthetic strategies. Herein, we developed a series of helical βisoindigo-based BÀ OÀ B bridged aza-BODIPY analogs that were synthesized conveniently. The reaction of diimino-β-isoindigo with a heteroaromatic amine produced a restricted ligand cavity, which triggered off the generation of a BÀ OÀ B bridge. The BÀ OÀ B bridge led to distorted conformations that satisfy the helical requirements, resulting in excellent spectroscopic and chiroptical properties. Tunable CPL with the highest luminescence dissymmetry factor (g lum ) of 1.3 × 10 À 3 and a CPL brightness (B CPL = 11.5 M À 1 cm À 1 ) in the NIR region was achieved. This synthetic approach is expected to offer a new opportunity to chiral chemistry and increase flexibility for chiroptical tuning.

Rational Design of Circularly Polarized Luminescent Molecular Structures Toward NIR and Single Molecule White Light Emission

“…As illustrated in Scheme 1, two molecules, (R)/(S)-BIT and (R)/(S)-BITM, were synthesized by coupling NIR chromophore derivatives with axial chiral binaphthol (BINOL) in dry DMF at 80 °C for 12 h. The chemical structures of target molecules were confirmed through 1 H NMR, 13 C NMR, and mass spectra (MS), as detailed in the Supporting Information. Differential scanning calorimetry (DSC) results indicated that (R)/(S)-BIT and (R)/(S)-BITM exhibited high thermal stability, with melting temperatures (T m ) at 230 and 210 °C, and sublimation temperatures (T s ) as high as 380 and 384 °C, respectively (Figure S1, Supporting Information).…”

“…For organic small-molecule CPL materials, the current research mainly focuses on single-color visible emission regions, while single-molecule white light emission (SMWLE) or near-infrared (NIR) luminescence materials with CPL were rarely reported. [13] So far, only one work on the circularly polarized white light (CPWL) and two articles on NIR-CPL have been reported. Duan et al developed a CPL-active chiral emitter derived from guanidinesubstituted 1,8-naphthalimide (R/S-1), which exhibited singlemolecule white-color circularly polarized emission (CIE = 0.35, 0.36).…”

Metal Halide Perovskite Nanocrystals for Near-Infrared Circularly Polarized Luminescence with High Photoluminescence Quantum Yield via Chiral Ligand Exchange

“…As one of the novel optical properties of chiral materials, circularly polarized luminescence (CPL) in different wavelength regions is of strong interest in photonics applications. − In particular, the near-infrared (NIR) CPL has potential applications in chiral synthesis, biology, and communication, attributed to its combination of chiral characteristics and high penetration. − To date, few NIR CPL materials have been reported, mainly based on lanthanide complexes, , organic helical polymers, , and small organic molecules (SOM). , However, these materials suffer from a low photoluminescence quantum yield (PLQY) and complex preparation. The lanthanide complexes tend to have a relatively high dissymmetry factor ( g lum ) besides low PLQY, which is attributed to the Laporte-forbidden nature. , Meanwhile, according to energy gap theory, the design of organic molecules for superior NIR CPL (650–900 nm) is highly difficult. , Both helical polymers and SOM used for NIR CPL have low PLQY as well as requiring tedious preparation. − …”

“…1−3 In particular, the near-infrared (NIR) CPL has potential applications in chiral synthesis, biology, and communication, attributed to its combination of chiral characteristics and high penetration. 4−6 To date, few NIR CPL materials have been reported, mainly based on lanthanide complexes, 5,7 organic helical polymers, 8,9 and small organic molecules (SOM). 10,11 However, these materials suffer from a low photoluminescence quantum yield (PLQY) and complex preparation.…”

“…12,13 Meanwhile, according to energy gap theory, the design of organic molecules for superior NIR CPL (650−900 nm) is highly difficult. 9,14 Both helical polymers and SOM used for NIR CPL have low PLQY as well as requiring tedious preparation. 8−11 Metal halide perovskites have great potential for superior NIR CPL due to their extreme brightness, high PLQY, and coverage of visible to NIR optical emission.…”