A C-H activation-based enantioselective synthesis of lower carbo[n]helicenes

The three-dimensional structure of carbohelicenes has fascinated generations of molecular chemists and has been exploited in a wide range of applications. Their strong circularly polarized luminescence has attracted considerable attention in recent years due to promising applications in new optical materials. Although the enantioselective synthesis of fused carbo- and heterohelicenes has been achieved, a direct catalytic enantioselective method allowing the synthesis of lower, non-fused carbo[n]helicenes (n = 4-6) is still lacking. We report here that Pd-catalysed enantioselective C-H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[n]helicenes. Computational mechanistic studies indicate that both the C-H activation and reductive elimination steps contribute to the overall enantioselectivity. The observed enantio-induction seems to arise from a combination of non-covalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. The photophysical and chiroptical properties of the synthesized scalemic [n]helicenes have been systematically studied

Synthesis, structural characterization, and chiroptical properties of planarly and axially chiral boranils

International audience2-Amino[2.2]paracyclophane reacts with salicylaldehyde or 2-hydroxyacetophenone to yield imines that then give access to a new series of boranils (8b–d) upon complexation with BF2. These novel boron-containing compounds display both planar and axial chiralities and were examined experimentally and computationally. In particular, their photophysical and chiroptical properties were studied and compared to newly prepared, simpler boranils (9a–d) exhibiting axial chirality only. Less sophisticated chiral architectures were shown to demonstrate overall stronger circularly polarized luminescence (CPL) activity

Circularly polarized-thermally activated delayed fluorescent materials based on chiral bicarbazole donors

G. P. thanks the SCBM, the “PTC du CEA” (POLEM) and the ANR (iChiralight, ANR-19-CE07-0040) for funding and David Buisson, Amélie Goudet and Sabrina Lebrequier. J. C. and L. Fa. acknowledge the Ministère de l’Education Nationale, de la Recherche et de la Technologie, the CNRS and the Spectroscopies-CDTP core facility is also acknowledged. The St. Andrews team thanks the China Scholarship Council, 201906250199 to W. S. and 202006250026 to J. W., E. Z.-C. is a Royal Society Leverhulme Trust Senior Research fellow (SRF\R1\201089). We thank the EPSRC (EP/R035164/1) for funding.We describe herein a molecular design to generate circularly polarized thermally activated delayed fluorescence emitters in which chiral bicarbazole donors are connected to acceptor units via a rigid 8-membered cycle and how the nature of the donor and acceptor units affect the photophysical and chiroptical properties.Publisher PDFPeer reviewe

Synthesis of chiral fluorescent molecules

Les molécules émettrices de lumière circulairement polarisée (CPL) possèdent un fort potentiel d'application dans de nombreux domaines tels que dans le stockage optique d'informations, les technologies anti-contrefaçon ou encore en tant que dopants dans les couches émettrices de dispositifs électroluminescents. D'un point de vue plus fondamental, un des défis d'aujourd'hui consiste à imaginer des concepts moléculaires permettant de combiner l'émission de CPL avec d'autres types de propriétés de luminescence (comme l'émission de fluorescence retardée, TADF, ou de la fluorescence par transfert de proton intramoléculaire a l'état excité, ESIPT). Ces travaux de thèse explorent plusieurs aspects de cette thématique recherche. Dans une première partie, les premières molécules combinant des propriétés de CPL et d'ESIPT ont été développées et leurs propriétés ont été étudiées et rationnalisées à l'aide de calculs théoriques. Elles ont également été utilisées en tant que “switchs” chiroptiques. Deux autres chapitres se concentrent sur la conception, et l'étude de molécules possédant des propriétés d'émission de TADF et de CPL ainsi que sur l'optimisation de leurs propriètés via une étude des relations structures propriétés approfondies. Enfin, un dernier chapitre porte sur la synthèse et l'étude de nouveaux émetteurs de CPL constitués d'un motif chiral configurationnellement stable accolé à fluorophore actif de type donneur-accepteur de géométrie hélicoidale de faible stabilité conformationnelle.Molecules displaying circularly polarized luminescence (CPL) have numerous potential applications in many fields such as optical data storage, anti-counterfeiting technologies and more notably as emissive material in electroluminescent devices. From a fundamental point of view, one of today's challenge is to combine CPL emission with other peculiar properties such as TADF (Thermally Activated Delayed Fluorescence) or ESIPT (Excited State Intramolecular Proton Transfer). This works aims to explore several aspects of this thematic. Thus, in a first project, the first molecules combining CPL emission with ESIPT has been developed, studied and used as a chiroptical switch. Two other chapters of this thesis focus on the conception and study of fluorophores combining TADF emission with CPL emission as well as the optimization of their photophysicals and chiropticals properties through a structure-activity relationship study. Lastly, the study and the synthesis of new CPL emitters with both a configurationally stable chiral moieties and a twisted donor-acceptor with a low stability helicoidal geometry has been performed

Excited State Intramolecular Proton Transfer Based Fluorophores with Circularly Polarized Luminescence Emission

International audienceAbstract Herein, the first molecular design allowing the combination of circularly polarized luminescence (CPL) and excited state intramolecular proton transfer (ESIPT) fluorescence is described. In this novel class of emitters, the chiroptical activity originates from a chiral excitonic coupling induced by the tethering of two ESIPT fluorophores via a readily accessible trans ‐1,2‐diaminocyclohexane scaffold. This approach has notably allowed the synthesis in a single step of a CPL‐active molecule displaying a very large Stokes shift (up to 12 087 cm −1 in toluene solution) and the synthesis in three steps of one of the rare examples of CPL‐active purely organic dual‐emission materials

Chiral perturbation on single benzene‐based fluorophores: A structure/(chir)optical activity relationship study

International audienceAbstract In this paper, we describe the synthesis and the (chir)optical properties of a novel series of circularly polarized luminescent emitters. These molecules involve a compact single benzene‐based donor‐acceptor fluorophore composed of two cyclic alkylamines as electron donors and a phthalonitrile moiety as electron acceptor linked to a configurationally stable BINOL acting as a chiral perturbation unit. These new compounds display fair quantum yields (up to 66%) with emission maxima around 500 nm in toluene solutions, and the study of their chiroptical properties has shown that the cyclic alkylamine's ring size affects significantly the luminescence dissymmetry factors, reaching 2.2 × 10 −3 for the larger cyclic alkylamine moieties

A C-H Activation-Based Enantioselective Synthesis of Lower Carbo[n]helicenes (n = 4-6)

The unique three-dimensional structure of carbohelicenes have fascinated generations of molecular chemists and has been exploited through a wide range of applications. In particular, their strong circularly polarized luminescence (CPL) has raised much attention in recent years due to promising applications in the design of new optical materials. Whereas a number of important precedents report enantioselective syntheses of fused carbo- and heterohelicenes, a direct catalytic enantioselective method allowing the synthesis of lower, nonfused carbo[n]helicenes (n = 4-6) is still lacking. We report that Pd-catalysed enantioselective C–H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these simple carbo[n]helicenes. Computational mechanistic studies indicate that both the C–H activation and reductive elimination steps contribute to the overall enantioselectivity. In addition, the observed enantio-induction seems to arise from a combination of noncovalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. Moreover, the current method allows a comparative study of the CPL properties of lower carbo[n]helicenes, which led to the discovery that carbo[4]helicenes actually display CPL responses comparable to the higher carbo[6]helicene congeners

Synthesis, structural characterization and chiroptical properties of lanarly and axially chiral boranils

International audience2-Amino[2.2]paracyclophane reacts with salicylaldehyde or 2-hydroxyacetophenone to yield imines that then give access to a new series of boranils (8b–d) upon complexation with BF2. These novel boron-containing compounds display both planar and axial chiralities and were examined experimentally and computationally. In particular, their photophysical and chiroptical properties were studied and compared to newly prepared, simpler boranils (9a–d) exhibiting axial chirality only. Less sophisticated chiral architectures were shown to demonstrate overall stronger circularly polarized luminescence (CPL) activity

Circularly polarized-thermally activated delayed fluorescent materials based on chiral bicarbazole donors

We describe herein a molecular design to generate circularly polarized thermally activated delayed fluorescence emitters in which chiral bicarbazole donors are connected to acceptor units via a rigid 8-membered cycle and how the nature of the donor and acceptor units affect the photophysical and chiroptical properties

Stable π‑Extended Thio[7]helicene-Based Diradical with Predominant Through-Space Spin–Spin Coupling

In this work, a novel π-extended thio[7]helicene scaffold was synthesized, where the α-position of the thiophene unit could be functionalized with bulky phenoxy radicals after considerable synthetic attempts. This open-shell helical diradical, ET7H-R, possesses high stability in the air, nontrivial π conjugation, persistent chirality, and a high diradical character (y0 of 0.998). The key feature is a predominant through-space spin–spin coupling (TSC) between two radicals at the helical terminals. Variable-temperature continuous-wave electron spin resonance (cw-ESR) and superconducting quantum interference device (SQUID) magnetometry in the solid state reveal a singlet ground state with a nearly degenerate triplet state of ET7H-R. These results highlight the significance of a stable helical diradicaloid as a promising platform for investigating intramolecular TSCs