Synthesis and Chiroptical Properties of Chiral Carbazole-Based BODIPYs

Recent Advances of Chiral Isolated and Small Organic Molecules: Structure and Properties for Circularly Polarized Luminescence

This paper explores recent advancements in the field of circularly polarized luminescence (CPL) exhibited by small and isolated organic molecules. The development and application of small CPL molecule are systematically reviewed through eight different chiral skeleton sections. Investigating the intricate interplay between molecular structure and CPL properties, the paper aims at providing and enlighting novel strategies for CPL-based applications.

A series of boron difluoride complexes of azinylcarbazoles: synthesis and structure-property relationships

A series of boron difluoride (BF₂) complexes of azinylcarbazoles 1b-1h were synthesized, and the effects of the structure of azine moieties on the photophysical and electrochemical properties of the BF₂ complexes were clarified. UV-vis analysis of 1b with quinoline, 1c with isoquinoline, and fully fused 1d revealed that fusion with a benzene ring to a pyridylcarbazole BF₂ complex (1a) resulted in red shifts of longest-maximum absorption wavelengths (λ_max). UV-vis analysis of 1e and 1f with pyrimidine, 1g with pyridazine, and 1h with pyrazine revealed that substitution of a carbon atom to a nitrogen atom in 1a also resulted in red shifts of λ_max. The fluorescence quantum yields (Φ_f) decreased from 1a to 1b-1h, and especially, the fluorescence of 1e, 1g, and 1h was quenched in solution. At 77 K, the emission intensities of 1b-1h were significantly increased compared with those at ambient temperature, and they also exhibited phosphorescence with relatively narrow energy gaps between the singlet and triplet excited states. These results on the emission at 77 K indicate that the quench of fluorescence from 1e, 1g, and 1h at ambient temperature originates from both internal conversions and intersystem crossing. In the solid state, all of the complexes including 1e, 1g, and 1h exhibited emission. Distinctive aggregation-induced emission properties were observed for 1e-1h. Electrochemical measurements revealed that the replacement of the pyridine moiety in 1a with azine moieties reduced electrochemical gaps mainly due to a decrease in the LUMO levels. The effects of azine moieties on electronic structures were also discussed based on theoretical calculations.

Phenothiazine-, Dihydroacridine-, and Acridone-Based Boron Difluoride Complexes: Synthesis and Structure-Property Relationships

Boron difluoride complexes of phenothiazine, 9,10-dihydroacridine, and acridone derivatives with a pyridyl group were synthesized. Their structures, dynamic conformational behaviors, and photophysical properties, including solid-state fluorescence, were disclosed. The effects of the oxidation state of the sulfur atom in the phenothiazine derivatives on their properties were also clarified.

Synthesis, Characterization, and Properties of BN-Fluoranthenes

Boron/nitrogen-doped fluoranthenes, a new class of BN-doped cyclopenta-fused polycyclic aromatic hydrocarbons, were synthesized via pyrrolic-type nitrogen directed C-H borylation. Regioselective bromination of BN-fluoranthene (3a) gave mono- and dibrominated BN-fluoranthenes. The halogenated BN-fluoranthene (3b) can undergo various of further cross-coupling reactions to deliver a series of BN-fluoranthenes. Moreover, incorporating BN unit in to fluoranthene resulted in a wider HOMO-LUMO energy gaps. The aromaticities of the BN-fluoranthene (3a) were quantified by experimental and computational studies.

Highly contorted superhelicene hits near-infrared circularly polarized luminescence

Herein we describe a novel superhelicene structure consisting of three hexa-peri-hexabenzocoronene (HBC) units arranged in a helical geometry and creating two carbo[5]helicenes and a carbo[7]helicene. The central HBC bears a...

Facile Synthesis of Azahelicenes and Diaza[8]circulenes through the Intramolecular Scholl Reaction

Carbazole-based aza[7]helicenes and hetero[9]helicenes were successfully obtained via the intramolecular Scholl reaction of 3,6-bis(biphenyl-2-yl)carbazole congeners, while the reaction of 3,6-bis(naphthylphenyl)-appended carbazole gave a triple helicene via an unexpected simultaneous double aryl rearrangement. DFT calculations suggested that the rearrangement proceeded via an arenium cation intermediate. In addition, the reaction of methoxy-appended substrate gave an azahepta[8]circulene via the concurrent C-C bond formation. These helical dyes showed circularly polarized luminescence. The azahepta[8]circulene was further transformed into deeply saddle-distorted dibenzodiaza[8]circulenes as the first example of its solution-based synthesis and unambiguous structural determination.

Solution-Processable Chiral Boron Complexes for Circularly Polarized Red Thermally Activated Delayed Fluorescent Devices

Circularly polarized luminescence (CPL) molecules, especially those with thermally activated delayed fluorescence (TADF) properties, have attracted considerable attention due to their great potential for chiroptical organic light emitting diode (OLED) devices. Here we developed a new pair of TADF emitters with CPL based on boron complexes using chiral donor (cD) binaphthalene, acceptor (A) biphenyl boron β-diketonate, and donor (D) biphenylamine in a cD-A-D architecture. With this design, both efficient intramolecular charge transfer (ICT) and chiral ICT for high-performance CPL were established, leading to high dissymmetry factors (|g_lum|) up to 2.2 × 10^-3 in solution and significantly red-shifted emission around 600 nm for red TADF with a quantum yield over 15% in doped films. More impressively, with these chiral TADF emitters, solution-processed red circularly polarized OLEDs (CP-OLEDs) exhibit external quantum efficiencies (EQEs) up to 2.0% and efficient circularly polarized electroluminescence with dissymmetry factors of 2.6 × 10^-3, which are among the best performances of the reported solution-processed orange-red and red TADF CP-OLEDs. These results illustrate the great success of the cD-A-D strategy in designing high-performance CPL TADF emitters with axially chiral boron complexes, providing important clues to understand efficient chiral transfer for large |g_lum| values and high device performance of CP-OLEDs.

Chiral Benzothiazole Monofluoroborate Featuring Chiroptical and Oxygen-Sensitizing Properties: Synthesis and Photophysical Studies

Advances in personalized medicine are prompting the development of multimodal agents, that is, molecules that combine properties promoting various diagnostic and therapeutic applications. General approaches exploit chemical conjugation of therapeutic agents with contrast agents or the design of multimodal nanoplatforms. Herein, we report the design of a single molecule that exhibits potential for different diagnostic modes as well as the ability to sensitize oxygen, thus offering potential for photodynamic therapy. Exceptionally, this work involves the synthesis and chiral resolution of an enantiomeric pair of chiral monofluoroborates that contain a stereogenic boron atom. Combining experimental and theoretical chiroptical studies allowed the unambiguous determination of their absolute configuration. Photophysical investigations established the ability of this compound to sensitize oxygen even in the absence of heavy atoms within its structure. The synthesis of a chiral benzothiazole monofluoroborate paves a way to multimodal diagnostic tools (fluorescence and nuclear imaging) while also featuring potential therapeutic applications owing to its ability to activate oxygen to its singlet state for use in photodynamic therapy.

Synthesis and Optical Properties of Axially Chiral Bibenzo[b]carbazole Derivatives

Pure organic materials with the circularly polarized luminescence (CPL) property have attracted significant research interest over the past few decades. In this study, a series of axially chiral bibenzo[b]carbazole derivatives were synthesized by adopting palladium- and iridium-catalyzed direct C-H functionalization reactions as the key steps. These compounds exhibited CPL characteristics with considerably large dissymmetry factors up to 2.81 × 10^-2 in the solid state, indicating the formation of well-ordered aggregates.

Studying the reactivity of alkyl substituted BODIPYs: first enantioselective addition of BODIPY to MBH carbonates

The first enantioselective addition of alkyl BODIPYs to Morita-Baylis-Hillman (MBH) carbonates is reported. This is the first reported enantioselective methodology using the methylene position of BODIPYs as a nucleophile. The reaction is efficiently catalyzed by cinchona alkaloids, achieving high enantioselectivities and total diastereoselectivity. The use of cinchona alkaloid pseudo enantiomers (chinine/cinchonine) allows us to obtain both pairs of enantiomers in similar yields and enantioselectivities, a common issue in this type of reaction. The photophysical study of these dyes (absorption and fluorescence) has been performed in order to determine their parameters and explore future possible application in bioimaging. In addition, electronic circular dichroism (ECD) studies supported by time-dependent density functional theory (TD-DFT) calculations were also performed.

Ultrastrong Red Circularly Polarized Luminescence Promoted from Chiral Transfer and Intermolecular Förster Resonance Energy Transfer in Ternary Chiral Emissive Nematic Liquid Crystals

Chiral emissive liquid crystals (N*-LCs) have been proved to greatly amplify the circularly polarized luminescence (CPL) signals due to highly regular spiral arrangement of dyes in a well-organized liquid crystals system. Normally, CPL materials with a high luminescence dissymmetry factor (g_lum) and quantum yield (QY) can meet the real application requirement. Here, four chiral aggregate-induced emission (AIE) active donors (Guests A1-A4: R-C2, R-C4, R-C6, R-C8, chiral dopant, and energy donor) and achiral AIE-active acceptors (Guest B: PBCy, CPL emitter) were doped into the commercial nematic liquid crystals E7 (N-LCs, Host) to form CPL-active ternary chiral emissive N-LCs (T-N*-LCs), respectively. This kind of T-N*-LCs could emit strong red CPL with QY = 16.56% and g_lum up to 1.51 through intermolecular energy transfer and chirality induction from the supramolecular self-assembly of T-N*-LCs. This work provides the effective strategy for the development of high g_lum CPL materials.

Synthesis and electronic properties of carbazole-based core-modified diporphyrins showing near infrared absorption

Directly linked carbazole-based core-modified diporphyrin D2 and fused diporphyrin F2 were synthesized. These diporphyrins showed significant electronic interactions and conjugation allowing for redshifted near infrared (NIR) absorption and small HOMO-LUMO gaps as confirmed by NIR absorption spectroscopy, cyclic voltammetry (CV) measurements, and DFT calculations.

Aggregation-Induced Circularly Polarized Luminescence from Boron Complexes with a Carbazolyl Schiff Base

A variety of carbazolyl-appended Schiff bases were readily synthesized from 1-formylcarbazoles and aniline derivatives. Boron complexation of the resulting ligands allowed for facile preparation of new carbazole-based BODIPY analogues showing solid-state fluorescence. Furthermore, some dyes were converted into chiral compounds through the Et₂ AlCl-mediated incorporation of a binaphthyl unit. The chiral dyes showed aggregation-induced fluorescence and circularly polarized luminescence (CPL) with the Φ_F and g_lum of up to 0.22 and -3.5×10^-3 , respectively, in the solid state. The solid-state fluorescence and CPL were well characterized by the crystal packing analyses and DFT calculations.