Sign control of circularly polarized luminescence of chiral Schiff-base Zn(II) complexes through coordination geometry changes.

The handedness of circularly polarized luminescence (CPL) of Zn(II) complexes with a chiral Schiff-base ligand can be controlled by coordination geometry changes in solution and in the solid state. The relationships between molecular structure and chiroptical properties were discussed with the results of X-ray diffraction analysis and DFT calculations.

Multi-colour circularly polarized luminescence properties of chiral Schiff-base boron difluoride complexes.

A series of chiral Schiff-base boron difluoride complexes was synthesized and their photophysical properties were examined. These complexes showed multi-colour (blue, yellow and red) photoluminescence in solution and in the solid state with good emission quantum yield (Φ) depending on the π-systems of the ligands. The chiral complexes exhibited circularly polarized luminescence (CPL) with an absolute luminescence dissymmetry factor (glum) of up to the 1.3 × 10-3 in solution and 1.9 × 10-2 in the drop-cast film state. Density functional theory (DFT) and time-dependent (TD) DFT calculations were conducted to further understand the photophysical properties.

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

Invited for this month's cover picture are the groups of Masahiro Ikeshita and Takashi Tsuno at Nihon University and Yoshitane Imai at Kindai University (Japan). The cover picture shows the comparison of circularly polarized luminescence (CPL) properties of square planar platinum(II) complexes with different coordination geometry. Computational studies have been carried out to investigate these structure-dependencies, and revealed that the distortion of the coordination geometry results into an enhancement the chiroptical responses of these compounds. Read the full text of their Research Article at 10.1002/open.202100277.

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

The relationship between the coordination geometry and photophysical properties of trans-bis[(ß-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.

Magnetic Circularly Polarized Luminescence from PtII OEP and F2 -ppyPtII (acac) under North-up and South-up Faraday Geometries.

The magnetic circularly polarized luminescence (MCPL) and photoluminescence (PL) spectra of achiral (2,3,7,8,12,13,17,18-octaethylporphyrinato)platinum(II), PtOEP, and [2-(4',6'-difluorophenyl)pyridinato-N,C2' ]platinum(II) acetylacetonate-O,O, F2 -ppyPt(acac), in toluene and dichloromethane solutions were recorded under an external magnetic field of 1.6 T with N-up and S-up Faraday geometries. The MCPL signs of PtOEP and F2 -ppyPt(acac) were controlled solely by changing the N-up and S-up geometries. The MCPL/PL wavelengths of F2 -ppyPt(acac) in solutions were varied by the ratio of the monomeric and excimeric species.

Sign inversion of magnetic circularly polarized luminescence in Iridium(iii) complexes bearing achiral ligands.

Optically inactive, paramagnetic Ir(iii)(ppy)3 and Ir(iii)(ppy)2(acac) (ppy: 2-phenylpyridinate and acac: acetylacetonate) showed nearly mirror-symmetric magnetic circularly polarised luminescence (MCPL) spectra in dilute dichloromethane and dimethyl sulfoxide under N-up and S-up geometries in a 1.6-T magnetic field. However, the MCPL signs of Ir(iii)(ppy)3 and Ir(iii)(ppy)2(acac) under the same N-up (or S-up) Faraday geometry were opposite to each other when one ppy was replaced with an acac. This ligand exchange approach provides facile control of the MCPL sign, irrespective of the Faraday geometry.