ABSTRACT
Finely controlled circularly polarized luminescence (CPL) supramolecular polymerization based on a tetraphenylethene core with four l- or d-alanine branch side chains (l-1 and d-1) in the solution state is presented, resulting from the tuning of mechanical stimulus. Weak, green emissions of l-1 and d-1 in tetrahydrofuran (THF) were converted into strong blue emissions by tuning the mechanical stimulus. The strong blue emissions were caused by an aggregation-induced emission (AIE) effect during the formation of a supramolecular polymer. Lag time in the supramolecular polymerization was drastically reduced by the mechanical stimulus, which was indicative of the acceleration of the supramolecular polymerization. A significant enhancement of circular dichroism (CD) and CPL signals of l-1 and d-1 was observed by tuning the rotational speed of the mechanical stimulus, implying that the chiral supramolecular polymerization was accelerated by the mechanical stimulus.
ABSTRACT
Chiral guest binding on a self-assembly of a bichromophoric naphthalenediimide (NDI) derivative is modulated in response to pressure. The intermolecular packing in the supramolecular polymer is strengthened at high pressure, compressing the binding pockets and discharging the guest molecules.
ABSTRACT
Two difluoro-boron ß-diketonate complexes bearing chiral amido groups have been synthesized. Their mechano-responsive luminescence and chiroptical properties have been investigated in the solid state. Both compounds display a bright blue-green emission and a significant circularly polarized luminescence (CPL) signal in the crystalline state, with |g lum| values as high as 2.2-2.4 × 10-2. A bathochromic shift in emission, together with a decrease of |g lum| values to c.a. 3 × 10-3, is induced upon application of a shearing stress. For the DFB-Hex-amide compound, interestingly, sign inversion of the anisotropy factor g lum is observed under mechanical stimulation ("mechano-CPL effect"), which can be rationalized by a switching between monomer and excimer emission.
ABSTRACT
Supramolecular ordering and orientation of chromophores are tremendously accomplished in photosynthetic light harvesting complexes, which are crucial for long-range transfer of collected solar energy. We herein demonstrate the importance of optical purity on the organization of chromophoric chiral molecules for efficient energy migration. Enantiomeric bichromophoric compounds, which self-assemble into nanofibers capable of chiral recognition, were mixed to form supramolecular coassemblies with variable enantiopurity. The chiral molecules self-assembled into extended fibers regardless of enantiopurity, while their morphology was dependent on the enantiomeric excess. The optical purity of assemblies also had an effect on the emission efficiency; the nanofibers with higher enantiomeric excess afforded a larger emission quantum yield. The presence of an opposite enantiomer is considered to deteriorate the chiral molecular packing suitable for directional growth of the nanofiber, efficient exciton migration, and chiral guest recognition.
ABSTRACT
Self-assembling molecular systems often display amplified chirality compared to the monomeric state, which makes the molecular recognition more sensitive to chiral analytes. Herein, we report the almost absolute enantioselective recognition of a chiral perylenediimide (PDI) molecule by chiral supramolecular nanofibers of a bichromophoric naphthalenediimide (NDI) derivative. The chiral recognition was evaluated through the Förster resonance energy transfer (FRET) from the NDI-based host nanofibers to the guest PDI molecules. The excitation energy was successfully transferred to the guest molecule through efficient energy migration along the host nanofiber, thus demonstrating the light-harvesting capability of these hybrid systems. Furthermore, circularly polarized luminescence (CPL) was enantioselectively sensitized by the guest molecule as the wavelength band and sign of the CPL signal were switched in response to the chiral guest molecule.
