In the solid state, amino acids (alanine and phenylglycine) with appended pyrene segments self‐assembled into α‐helix‐like structures by asymmetrical H‐bonds between carboxylic acid and amide segments, further inducing supramolecular tilted chirality of the achiral pyrenes. These structures bind melamine and electron‐deficient units through H‐bond and charge‐transfer interactions, respectively. Charge‐transfer interactions enhance the dissymmetry g‐factor of absorption (gabs; up to 1.4×10−2) with an extended Cotton effect active region (from 250 to 600 nm). Incorporating melamine inverts the handedness of circularly polarized luminescence and boosts the dissymmetry g‐factor (glum). Melamine also induces macroscopic chirality at the nanoscale, whereby the 2D lamellar structures are transformed into 1D helices at the nanoscale, leading to giant tubular structures at the microscale.
Deep understanding of structure–property relationship between packing of chiral building units and their chiroptical behaviors would significantly facilitate the rational design and fabrication of the emerging chiroptical materials such as circularly polarized luminescence (CPL) emissive materials. In this paper, we unveil the universal existence of supramolecular tilt helical superstructures in self‐assembled π‐conjugated amino acid derivatives. A series of coded amino acid methyl esters were conjugated to anthracene segments at N‐terminus, which afforded 21 and 31 symmetry supramolecular tilt chirality in solid‐states. Helical assemblies enabled diversified Cotton effects and CPL performances, which were in accordance with the tilted chirality between anthracene segments. Such correlation shows fine universality, whereby the chiroptical prediction could be realized. Furthermore, on top of charge‐transfer complexation, manipulation of CPL emission colors and handedness were realized.
Charge‐transfer (CT) complexation between electron‐rich and deficient aromatics has been widely applied in functional optical and photovoltaic materials. The selective complexation and spontaneous disassociation behavior of a dynamic charge‐transfer coassembly possess potential in designing smart and dynamic luminescent materials, which however have not been addressed so far. In this work, the transient charge‐transfer driven coassembly between π‐conjugated amino acids and tetracyanobenzene, showing dynamic luminescent transition and circularly polarized luminescence (CPL) evolution property, is illustrated. Transient coassembly behaviors are independent to the diverse binding sites covering fluorene, naphthalene, and anthracene, attributed to the intramolecular CH…π interaction. Incorporation of fluorescent dyes enables a transient light harvesting process with hyperchromic CPL properties. Spontaneous green‐to‐red CPL transition hydrogels are also fabricated by embedding a competitive CT donor. Using a polymeric matrix treated by organic solvents, charge‐transfer coassembly is immobilized with diverse circularly polarized luminescence. Such sensitive complexation shows applications in moisture‐responsive luminescent materials and multiple luminescent color evolutions are realized.
Materials with chiroptical activity
in the near-infrared (NIR)
region are emerging candidates for photothermal agents responding
to circularly polarized light. However, design, synthesis, and application
of organic species with NIR chiroptical activity remain considerable
challenges. Here, we present a charge-transfer (CT) strategy to realize
chiroptical properties in the NIR region. The NIR chiroptical activity
facilitated photothermal performance, which could be tuned by circularly
polarized NIR light. The building unit of pyrene-conjugated amino
acid derivatives was self-assembled into helical structures with supramolecular
tilt chirality in a solid state. The space group and methyl esterification
were used to determine helicity parameters and chiroptical properties
including circularly polarized luminescence. The CT complexation between
pyrene-conjugated amino acid derivatives and the acceptor enabled
the absorbance at above 800 nm, inducing the Cotton effects in the
NIR-I region with dissymmetry g-factors at 10–3 magnitude, which were manipulated by the amino acid
domains. CT complexes behaved as efficient photothermal agents in
both the aqueous and solid phase. Due to the NIR Cotton effects, the
heating rate and maximum temperature could be readily controlled and
responded to the handedness of circularly polarized light. This work
used self-assembled π-conjugated amino acid derivatives and
a CT protocol to manipulate the chiroptical activity evolution in
the NIR region and realized circularly polarized light-controlled
photothermal performances.
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