Self-discriminating termination of chiral supramolecular polymerization: tuning the length of nanofibers.

Directing the supramolecular polymerization towards a preferred type of organization is extremely important in the design of functional soft materials. Proposed herein is a simple methodology to tune the length and optical chirality of supramolecular polymers formed from a chiral bichromophoric binaphthalene by the control of enantiomeric excess (ee). The enantiopure compound gave thin fibers longer than a few microns, while the racemic mixture favored the formation of nanoparticles. The thermodynamic study unveils that the heterochiral assembly gets preference over the homochiral assembly. The stronger heterochiral binding over homochiral one terminated the elongation of fibrous assembly, thus leading to a control over the length of fibers in the nonracemic mixtures. The supramolecular polymerization driven by π-π interactions highlights the effect of the geometry of a twisted π-core on this self-sorting assembly.

Circularly Polarized Luminescence in Chiral Aggregates: Dependence of Morphology on Luminescence Dissymmetry.

The self-assembly of a chiral perylene bisimide bichromophoric derivative possessing a 1,1'-binaphthalene bridge was investigated by adopting two different methodologies, leading to the formation of aggregates with dissimilar morphologies. The chiral nature of the aggregated structures was optically probed with the help of circular dichroism (CD), vibrational circular dichroism (VCD), and circularly polarized luminescence (CPL). The one-dimensional aggregates formed in methylcyclohexane (MCH) exhibited twice the value of luminescence dissymmetry factor (glum) when compared with the spherical aggregates formed in chloroform at higher concentration. The summation of excitonic couplings between the individual chromophoric units in an aggregated system is responsible for the remarkably high luminescence dissymmetry exhibited by the chiral aggregates. The nanostructures could be successfully embedded into polymer films, leading to the fabrication of solid-state materials with high CPL dissymmetry that can find novel applications in chiroptical sensing, memory, and light-emitting devices based on organic nanoparticles.

Circularly polarized luminescence in supramolecular assemblies of chiral bichromophoric perylene bisimides.

Chiral bichromophoric perylene bisimides are demonstrated as active materials of circularly polarized emission. The bichromophoric system exhibited circularly polarized luminescence with dissymmetry factors typical of that of similar organic chiral chromophoric systems in the monomeric state. Variation in solvent composition led to the formation of stably soluble helical aggregates through intermolecular interactions. A large enhancement in the dissymmetry of circularly polarized luminescence was exhibited by the aggregated structures both in the solution and solid states. The sum of excitonic couplings between the individual chromophoric units in the self-assembled state results in relatively large dissymmetry in the circularly polarized luminescence, thereby giving rise to enhanced dissymmetry factors for the aggregated structures. The spacer between chiral center and chromophoric units played a crucial role in the effective enhancement of chiroptical properties in the self-assembled structures. These materials might provide opportunities for the design of a new class of functional bichromophoric organic nanoarchitectures that can find potential applications in the field of chiroptical memory and light-emitting devices based on supramolecular electronics.

Fingerprint signatures of lanthanide circularly polarized luminescence from proteins covalently labeled with a ß-diketonate europium(III) chelate.

Fingerprint signatures of circularly polarized luminescence (CPL) are observed from Staphylococcus aureus nuclease (SNase), bovine serum albumin (BSA), and insulin (Ins) labeled with europium(III) complexes containing a ß-diketonate ligand, where SNase shows a virtually opposite CPL sign compared to those of BSA and Ins.

Nona-coordinated chiral Eu(III) complexes with stereoselective ligand-ligand noncovalent interactions for enhanced circularly polarized luminescence.

Circularly polarized luminescence (CPL) of chiral Eu(III) complexes with nona- and octa-coordinated structures, [Eu(R/S-iPr-Pybox)(D-facam)(3)] (1-R/1-S; R/S-iPr-Pybox, 2,6-bis(4R/4S-isopropyl-2-oxazolin-2-yl)pyridine; D-facam, 3-trifluoroacetyl-d-camphor), [Eu(S,S-Me-Ph-Pybox)(D-facam)(3)] (2-SS; S,S-Me-Ph-Pybox, 2,6-bis(4S-methyl-5S-phenyl-2-oxazolin-2-yl)pyridine), and [Eu(Phen)(D-facam)(3)] (3; Phen, 1,10-phenanthroline) are reported, and their structural features are discussed on the basis of X-ray crystallographic analyses. These chiral Eu(III) complexes showed relatively intense photoluminescence due to their (5)D(0) → (7)F(1) (magnetic-dipole) and (5)D(0) → (7)F(2) (electric-dipole) transition. The dissymmetry factors of CPL (g(CPL)) at the former band of 1-R and 1-S were as large as -1.0 and -0.8, respectively, while the g(CPL) of 3 at the (5)D(0) → (7)F(1) transition was relatively small (g(CPL) = -0.46). X-ray crystallographic data indicated specific ligand-ligand hydrogen bonding in these compounds which was expected to stabilize their chiral structures even in solution phase. CPL properties of 1-R and 1-S were discussed in terms of transition nature of lanthanide luminescence.

Circular dichroism and circularly polarized luminescence triggered by self-assembly of tris(phenylisoxazolyl)benzenes possessing a perylenebisimide moiety.

Chiral tris(phenylisoxazolyl)benzenes possessing a perylenebisimide moiety assembled to form helical stacks. The self-assembling behavior of the helical stacks responded to changes in solvent properties, temperature, and concentration. Strong circular dichroism (CD) and circularly polarized luminescence (CPL) of their assemblies were displayed, and were controlled by external stimuli.

Noncovalent ligand-to-ligand interactions alter sense of optical chirality in luminescent tris(ß-diketonate) lanthanide(III) complexes containing a chiral bis(oxazolinyl) pyridine ligand.

Highly luminescent tris[ß-diketonate (HFA, 1,1,1,5,5,5-hexafluoropentane-2,4-dione)] europium(III) complexes containing a chiral bis(oxazolinyl) pyridine (pybox) ligand--[(Eu(III)(R)-Ph-pybox)(HFA)(3)], [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)], and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)])--exhibit strong circularly polarized luminescence (CPL) at the magnetic-dipole ((5)D(0) → (7)F(1)) transition, where the [(Eu(III)(R)-Ph-pybox)(HFA)(3)] complexes show virtually opposite CPL spectra as compared to those with the same chirality of [(Eu(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Eu(III)(R)-Me-Ph-pybox)(HFA)(3)]. Similarly, the [(Tb(III)(R)-Ph-pybox)(HFA)(3)] complexes were found to exhibit CPL signals almost opposite to those of [(Tb(III)(R)-i-Pr-pybox)(HFA)(3)] and [(Tb(III)(R)-Me-Ph-pybox)(HFA)(3)] complexes with the same pybox chirality. Single-crystal X-ray structural analysis revealed ligand-ligand interactions between the pybox ligand and the HFA ligand in each lanthanide(III) complex: π-π stacking interactions in the Eu(III) and Tb(III) complexes with the Ph-pybox ligand, CH/F interactions in those with the i-Pr-pybox ligand, and CH/π interactions in those with the Me-Ph-pybox ligand. The ligand-ligand interactions between the achiral HFA ligands and the chiral pybox results in an asymmetric arrangement of three HFA ligands around the metal center. The metal center geometry varies depending on the types of ligand-ligand interaction.

Chemical-stimuli-controllable circularly polarized luminescence from anion-responsive π-conjugated molecules.

Introduction of a BINOL-boron moiety to dipyrrolyldiketones as precursors of anion-responsive π-conjugated molecules results in the formation of a chiral environment in the form of anion-free receptors and anion-binding complexes. Conformation changes by inversion (flipping) of two pyrrole rings as a result of anion binding can control the chiroptical properties of the anion receptors. In particular, appropriate pyrrole ß-substituents induce distorted receptor π-planes and, as a result, give larger circularly polarized luminescence (CPL), which can be tuned by chemical stimuli (anions). This is the first example of chemical-stimuli-responsive CPL properties.

Observation of chiral aggregate growth of perylene derivative in opaque solution by circularly polarized luminescence.

The concentration-dependent enhancement of the luminescence dissymmetry factor has suggested that pi-conjugated chiral perylene derivatives in a high concentrated opaque solution grow to aggregated structures with higher optical chirality.