Magnetic Circularly Polarized Luminescence in the Photoexcited States of Racemic [n]Helicenes (n=3-5,7) in Tetrahydrofuran and Dimethyl Sulfoxide Solutions

This paper reports the first magnetic circularly polarized luminescence (MCPL) characteristics of racemic helicenes, including four unsubstituted [n]helicenes (n=3,4,5,7) and two [4]helicene derivatives bearing methoxy substituents, in tetrahydrofuran (THF) and dimethyl sulfoxide (DMSO) solutions. The value of |g_MCPL | was calculated to be of the order of 10^-3  T^-1 within 350-430 nm under the north-up (N-up) and south-up (S-up) Faraday geometries in an external magnetic field of 1.6 T. The [n]-dependent MCPL signs were altered by the N-up and S-up geometries.

Remarkable Effects of External Magnetic Field on Circularly Polarized Luminescence of EuIII (hfa)3 with Phosphine Chirality

Herein, magnetic circularly polarized luminescence (CPL) (MCPL) spectroscopy was conducted to analyze an Eu^III (hfa)₃ complex with three chiral P^III -ligands. Resultantly, (R)-chirality luminophores with S-up orientation and (S)-chirality luminophores with N-up orientation were observed to possess symmetrical mirror image spectra, i. e., they were enantiomers. Similarly, the (R)-chirality luminophores with N-up orientation and the (S)-chirality luminophores with S-up orientation were also enantiomers. Contrarily, (R)-S-up and (S)-S-up were diastereomers and did not possess a mirror-image relationship. Likewise, (R)-N-up and (S)-N-up were diastereomers. The J-dependency of g_MCPL and g_CPL datasets suggested that the N-up/S-up external magnetic field, with the aid of chiral P^III -ligands, increased the g_MCPL values by two- to sixteen-fold and modulated the g_MCPL signs at J=1-4. Additionally, the origins of the nonideal mirror-symmetric CPL and MCPL spectral characteristics of Eu^III (hfa)₃ with three chiral P^III -ligands were discussed in terms of parity (space-inversion, P)-symmetry, time-reversal (T)-symmetry, and PT-symmetry laws.

Deep-red circularly polarised luminescent C70 derivatives

Optically active fullerenes, including C₆₀ and C₇₀ derivatives carrying organic substituents, are used in a range of applications because of their unique spectroscopic, catalytic, and chiral recognition properties. However, their inherent photoexcited chirality is yet to be elucidated because of their very poor fluorescence quantum yield (Φ_f). We synthesised a new chiral C₇₀ derivative, X70A, with 20% yield, by reacting bis-borylated xanthene with C₇₀ in a one-step double addition reaction, followed by a successful optical resolution. The isolation of two separate X70A enantiomers was confirmed by mirror-image circular dichroism spectroscopy in the range of 300–750 nm. In toluene, the enantiomeric pair of X70A clearly revealed mirror-image circularly polarised luminescence (CPL) spectra with a high |g_lum| value of 7.0 ×  10⁻³ at 690 nm. The first fullerene-based deep-red CPL of X70A should provide a new guideline for the design of chiral nanocarbon materials.

Sign dependence of MCPL spectra on type and position of substituent groups of pyrene and phenanthrene derivatives

Diamagnetic achiral pyrene and phenanthrene derivatives substituted with electron-donating hydroxyl/methoxy groups and electron-withdrawing carboxylic acid groups exhibited clear magnetic circularly polarised luminescence (MCPL) spectra at 360-460 nm in dilute solvents upon the application of N-up and S-up Faraday geometries under an external magnetic field of 1.6 T. Their MCPL signs were also susceptible upon application of the same Faraday geometry.

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.

Stereospecific Synthesis of Cyclic Sulfite Esters with Sulfur-Centered Chirality via Diastereoselective Strategy and Intramolecular H-Bonding Assistance

Stereospecific synthesis of several cyclic sulfite esters containing three stereogenic centers from enantiopure 1,1,4,4-tetraarylbutanetetraols was achieved. Chiral sulfur centers were constructed stereospecifically via a diastereoselective reaction with the assistance of an intramolecular H-bonding interaction. The absolute configuration of the S atom was elucidated by using the corresponding single-crystal X-ray diffraction analysis of the synthesized monochloride cyclic sulfite esters. Furthermore, a crystallographic evidence of the specific intramolecular C(sp³)-H···C_Ar weak H-bondings was presented, and its dramatic effect on the ¹H NMR spectral properties was revealed. This intriguing behavior was unambiguously rationalized by different shielding effects of the neighboring phenyl rings. Additionally, the theoretical results obtained on the basis of MP2 calculations fully supported the existence of intramolecular hydrogen bonding interactions being responsible for the observed unique chemical and spectral properties.

Sign inversion in magnetic circularly polarised luminescence of fused aromatics with 1.6 T N-up/S-up Faraday geometry

Although 12 diamagnetic fused aromatics with or without substituents exhibit mirror-symmetric magnetic circularly polarised luminescence (MCPL) through N-up and S-up Faraday geometries under a magnetic field intensity of 1.6 T, their signs (single and multiple) and magnitudes depend strongly on either the aromatic structures or the peripheral positions of the substituents.

Diamagnetic fused aromatics exhibit mirror-symmetric magnetic circularly polarised luminescence (MCPL) depend on either the aromatic structures or the peripheral positions of the substituents through N-up and S-up Faraday geometries under a 1.6 T magnetic field.

Chirogenesis and Pfeiffer Effect in Optically Inactive EuIII and TbIII Tris(β-diketonate) Upon Intermolecular Chirality Transfer From Poly- and Monosaccharide Alkyl Esters and α-Pinene: Emerging Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD)

We report emerging circularly polarized luminescence (CPL) at 4f-4f transitions when lanthanide (Eu^III and Tb^III) tris(β-diketonate) embedded to cellulose triacetate (CTA), cellulose acetate butyrate (CABu), D-/L-glucose pentamethyl esters (D-/L-Glu), and D-/L-arabinose tetramethyl esters (D-/L-Ara) are in film states. Herein, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate (fod) and 2,2,6,6-tetramethyl-3,5-heptanedione (dpm) were chosen as the β-diketonates. The g_lum value of Eu(fod)₃ in CABu are +0.0671 at 593 nm (⁵D0→7F₁) and −0.0059 at 613 nm (⁵D0→7F₂), respectively, while those in CTA are +0.0463 and −0.0040 at these transitions, respectively. The g_lum value of Tb(fod)₃ in CABu are −0.0029 at 490 nm (⁵D4→7F₆), +0.0078 at 540 nm (⁵D4→7F₅), and −0.0018 at 552 nm (⁵D4→7F₅), respectively, while those in CTA are −0.0053, +0.0037, and −0.0059 at these transitions, respectively. D-/L-Glu and D-/L-Ara induced weaker g_lum values at 4f-4f transitions of Eu(fod)₃, Tb(fod)₃, and Tb(dpm)₃. For comparison, Tb(dpm)₃ in α-pinene showed clear CPL characteristics, though Eu(dpm)₃ did not. A surplus charge neutralization hypothesis was applied to the origin of attractive intermolecular interactions between the ligands and saccharides. This idea was supported from the concomitant opposite tendency in upfield ¹⁹F-NMR and downfield ¹H-NMR chemical shifts of Eu(fod)₃ and the opposite Mulliken charges between F-C bonds (fod) and H-C bonds (CTA and D-/L-Glu). An analysis of CPL excitation (CPLE) and CPL spectra suggests that (+)- and (–)-sign CPL signals of Eu^III and Tb^III at different 4f-4f transitions in the visible region are the same with the (+)-and (–)-sign exhibited by CPLE bands at high energy levels of Eu^III and Tb^III in the near-UV region.

Mirror-image magnetic circularly polarized luminescence (MCPL) from optically inactive EuIII and TbIIItris(β-diketonate)

Five optically inactive Eu^III and Tb^III complexes with achiral organic ligands revealed north-up/south-up magnet geometry dependent mirror-image magnetic circularly polarized luminescence in solutions, in films and bulk powder under 1.6 Tesla.

Circularly polarised luminescence from planar-chiral Phanephos/Tb(iii)(hfa)3 hybrid luminophores

Planar-chiral Phanephos, containing the coordinatable P(iii), formed P(iii)/Tb(iii)(hfa)₃ hybrid luminophores that successfully emitted characteristic circularly polarised luminescence (CPL) due to ⁵D₄→⁷F₅ transitions in solution. On the other hand, BINAP, containing P(iii)[double bond, length as m-dash]O as axially chiral ligand, exhibited no detectable CPL with Tb(iii)(hfa)₃.