Linker-dependent control of the chiroptical properties of polymethylene-vaulted trans-bis[(β-iminomethyl)naphthoxy]platinum(II) complexes

The effects of polymethylene bridges on the chiroptical properties of trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms were examined both experimentally and theoretically using newly designed planar chiral Pt analogues (1) having three-dimensional superstructures. A series of optically pure polymethylene-vaulted Pt complexes (R)- and (S)-1 were synthesized and characterized with regard to the chiroptical behaviour of the trans-bis[(β-iminomethyl)naphthoxy]platinum(II) platforms. These complexes were found to exhibit structure-dependent chiroptical characteristics in solution, such that the absolute values of specific rotation, the circular dichroism dissymmetry factor (gabs) and the circularly polarized luminescence dissymmetry factor (glum) all increased upon shortening the polymethylene bridges. Density functional theory and time dependent density functional theory calculations were used to analyse vaulted and non-vaulted complexes, which demonstrated that the present linker-dependent chiroptical properties resulted from constraint-induced changes in the square planar Pt coordination centres rather than from chiral distortion along the coordination platforms.

Supramolecular Chirality Achieved by Assembly of Small π-Molecules of Octahydrobinaphtols with Axial Chirality

5,5',6,6',7,7',8,8'-Octahydro-1,1'-bi-2-naphthol (hbNaph) is an axially chiral molecule consisting of a smaller π-electronic system than that for 1,1'-bi-2-naphthol (BINOL). The absorption and circular dichroism (CD) bands of hbNaph appear in a shorter wavelength region below 310 nm, compared to those of BINOL, and its fluorescence is in the invisible UV region. However, increasing the concentration of hbNaph in solution up to 0.1 M results in its absorption edge gradually extending to longer wavelength, with a shoulder around 330 nm, and finally increasing to about 450 nm. At the same time, blue fluorescence is clearly observed, as well as a new CD band with the sign of the Cotton signals reversed from those obtained for dilute solutions. These results suggest that, at high concentrations, hbNaph forms chiral aggregates, in which π-electrons are delocalized over multiple molecules. To further understand how molecular axial chirality is transformed to supramolecular chirality, we attempted to construct aggregate models by simulating CD spectra using a time-dependent density functional theory. The only reasonable model obtained was that involving the counterclockwise R-enantiomer forming a clockwise helix, while the clockwise S-enantiomer forms a counterclockwise helix. We conclude, however, that, for such helixes, the most plausible model is densely packed and forms when the dihedral angle between the two phenol rings of hbNaph is acute, at around 75°, which reproduces the aggregate-induced CD sign inversion.

Enhancement of Chiroptical Responses of trans-Bis[(β-iminomethyl)naphthoxy]platinum(II) Complexes with Distorted Square Planar Coordination Geometry

The relationship between the coordination geometry and photophysical properties of trans‐bis[(β‐iminomethyl)naphthoxy]platinum(II) was investigated both experimentally and theoretically. A series of platinum(II) complexes with differently substituted iminomethyl groups were synthesized, and their photophysical properties were examined in solution, in the crystalline, and in the PMMA film‐dispersed state, respectively (PMMA=poly(methyl methacrylate)). These complexes showed structure‐dependent emission spectra, in which the color of the luminescence in the crystalline state varied over a range of about 40 nm depending on the specific bowl‐shaped molecular structure. The chiral complexes with (R,R)‐ and (S,S)‐configurations were found to have structure‐dependent chiroptical properties both in solution and the PMMA film‐dispersed state such that the intensity of circular dichroism (CD) and circularly polarized luminescence (CPL) were enhanced with bulky cyclic substituents at the nitrogen atoms. A theoretical study using density functional theory (DFT) and time‐dependent (TD)‐DFT calculations revealed that the enhancement of chiroptical responses is due to the amplification of the magnetic dipole moment caused by the distortion of the square planar geometry.

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.

Excimer-origin CPL vs. monomer-origin magnetic CPL in photo-excited chiral binaphthyl-ester-pyrenes: critical role of ester direction

Two chiral binaphthyl (BNp) derivatives bearing oppositely oriented ester linkers to two pyrene (Py) moieties [(R)/(S)-1 and (R)/(S)-2] enabled Py-origin circularly polarized luminescence (CPL), magnetic CPL (MCPL), and circular dichroism (CD). (R)-1 that exhibited (-)-sign CD showed (+)-sign Py-excimer CPL but did not exhibit MCPL. Conversely, (R)-2, with (-)-sign CD, did not show excimer-origin CPL, but exhibited clear Py-monomer MCPL.

Solvent-sensitive signs and magnitudes of circularly polarised luminescence and circular dichroism spectra: probing two phenanthrenes as emitters endowed with BINOL derivatives

A C₂-symmeric binaphthyl framework bearing phenanthrene as the emitter exhibited circularly polarised luminescence (CPL) in dilute solutions.

Phosphonoselenoic acid esters from the reaction between phosphoroselenoyl chlorides and Grignard reagents: synthetic and stereochemical aspects

Substitution reactions between a phosphoroselenoyl chloride and Grignard reagents proceeded smoothly at the phosphorus atom to furnish phosphonoselenoic acid esters in moderate to high yields.

Circularly Polarized Luminescence from Simple Organic Molecules

This article aims to show the identity of "circularly polarized luminescent active simple organic molecules" as a new concept in organic chemistry due to the potential interest of these molecules, as availed by the exponentially growing number of research articles related to them. In particular, it describes and highlights the interest and difficulty in developing chiral simple (small and non-aggregated) organic molecules able to emit left- or right-circularly polarized light efficiently, the efforts realized up to now to reach this challenging objective, and the most significant milestones achieved to date. General guidelines for the preparation of these interesting molecules are also presented.

Sign inversion of circularly polarized luminescence by geometry manipulation of four naphthalene units introduced into a tartaric acid scaffold

Tethering four 1- versus 2-naphthyls to the same chiral scaffold derived from tartaric acid led to oppositely signed circularly polarized luminescence (CPL) and circular dichroism (CD) in solution, which not only reveals the decisive role of the spatial arrangement of chromophores/fluorophores in determining the chiroptical behaviors but also provides us with a versatile tool for switching the signs of CPL and CD without using the antipodal scaffold.

Photoexcited state chirality transfer. Hidden tunability of circularly polarized luminescent binaphthyl–anthracene tandem molecular systems

Circularly polarized luminescent properties of binaphthyl with two achiral anthracenes were tuned by exploiting photoexcited-state chirality transfer from the binaphthyl to anthracenes when open- or closed-type binaphthyl structure was chosen.

Solid-state circularly polarised luminescence of atropisomeric fluorophores embedded in achiral myo-inositol-containing polyurethanes

Two chiral binaphthyl fluorophores in two myo-inositol based polyurethane matrices with high grass transition temperatures emitted circularly polarised luminescence with a high circular anisotropy factor.

Circularly polarized luminescence of biaryl atropisomers: subtle but significant structural dependency

The signs of circularly polarised luminescence and circular dichroism of chiral biaryl organic fluorophores in CHCl₃⁻ and PMMA film were successfully controlled by the internal axial chirality and the axial bonding position of biaryl units.

Circularly polarized luminescence by visible-light absorption in a chiral O-BODIPY dye: unprecedented design of CPL organic molecules from achiral chromophores

Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) O-BODIPYs (R)-1 and (S)-1 by irradiation with visible light is first detected as proof of the ability of a new structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|g(lum)|) in solution falls into the usual range of that obtained from other simple organic molecules (10(-5)-10(-2) range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1'-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications.

Nonclassical dual control of circularly polarized luminescence modes of binaphthyl–pyrene organic fluorophores in fluidic and glassy media

The fluorescent modes and signs of the circularly polarized luminescence of an axially chiral binaphthyl–pyrene organic fluorophore were successfully controlled by changing from a fluidic chloroform solution to a glassy poly(methyl methacrylate) solid film.

Enhancing circularly polarised luminescence by extending the π-conjugation of axially chiral compounds

π-Conjugated (R)- and (S)-2,2′-diphenyl-4-biphenanthrol (VAPOL) exhibited an efficient circularly polarised luminescence (CPL) (∼1.3 × 10⁻³) at 376 nm. By comparison, (R)- and (S)-3,3-diphenyl-2,2-bi-1-naphthol (VANOL) exhibited no CPL.