Time-controllable roll-up onset of polythiophene sheets into nanotubes that exhibit circularly polarized luminescence

Enhancement of Circularly Polarized Luminescence from Pulsating Nanotubules

Enhancing the dissymmetry factor (glum ) is a crucial issue in developing circularly polarized luminescence (CPL) materials. Herein, based on supramolecular self-assembly of diethyl l-glutamate-cyanodiarylethene (L-GC) in mixed solution of EtOH-H2 O with different water fraction, enhanced circularly polarized emission from pulsating nanotubules is realized. In the mixture of ethanol and water (30/70, v/v), L-GC self-assembles into roll-up-type dense nanotubes and shows l-CPL. Remarkably, by increasing the water fraction to 80% and 90%, the diameter of the roll-up nanotubes increases and the dissymmetry factor of the nanotubes is significantly enhanced from 6.9 × 10-3  (dense nanotubes) to 3.7 × 10-2 (loose nanotubes) because of the enhanced intermolecular interactions and more ordered supramolecular stacking when increasing the water fraction. An efficient way is provided here to realize the increase of the dissymmetry factor by only changing the composition of solvents.

Stimuli-Responsive Transformable Supramolecular Nanotubes

Supramolecular nanotubes produced by self-assembly of organic molecules can have unique structural features such as a one-dimensional morphology with no branching, distinguishable inner and outer surfaces and membrane walls, or a structure that is hollow and has a high aspect ratio. Incorporation of functional groups that respond to external chemical or physical stimuli into the constituent organic molecules of supramolecular nanotubes allows us to drastically change the structure of the nanotubes by applying such stimuli. This ability affords an array of controllable approaches for the encapsulation, storage, and release of guest compounds, which is expected to be useful in the fields of physics, chemistry, biology, and medicine. In this article, I review the supramolecular nanotubes developed by our group that exhibit morphological transformations in response to pH, chemical reaction, light, temperature, or moisture.

Photo-responsive hole formation in the monolayer membrane wall of a supramolecular nanotube for quick recovery of encapsulated protein

Nanotubes with a single monolayer membrane wall comprised of a synthetic glycolipid and one of two synthetic azobenzene derivatives were assembled. X-ray diffraction, infrared, UV-visible, and circular dichroism spectroscopy clarified the embedding style of the azobenzene derivatives in the membrane wall, revealing that, depending on their different intermolecular hydrogen bond strengths, one azobenzene derivative was individually dispersed whereas the other formed a J-type aggregate. The non-aggregated derivative was insensitive to UV irradiation due to tight fixation by the surrounding glycolipid. In contrast, the aggregated derivative was sensitive to UV irradiation, which induced trans-to-cis isomerization of the derivative and disassembly of the J-type aggregate. Subsequent dissociation of the derivative into the bulk solution resulted in the formation of many nanometer-scale holes in the membrane wall. Although a model protein encapsulated within the nanotubes was slowly released over time from the two open ends of the nanotubes without UV irradiation, exposure to UV irradiation resulted in faster, preferential release of the protein through the holes in the membrane wall. The present findings are expected to facilitate the development not only of efficient means of recovering guest compounds stored within nanotubes but also the development of novel stimuli-responsive capsules in biological and medical fields.

Phthalocyanine-Triggered Helical Dipeptide Nanotubes with Intense Circularly Polarized Luminescence

Nanotubes with circularly polarized luminescence (CPL) are attracting much attention due to many potential applications, such as chiroptical materials, displays, and sensing. However, it remains a challenge to change the assemblies of ordinarily molecular building blocks into CPL supramolecular nanotubes. Herein, the regulation of quite common dipeptide (Fmoc-FF) assemblies into unprecedented helical nanotubes exhibiting intense CPL is reported by simply doping a few phthalocyanine (octakis(carboxyl)phthalocyaninato zinc complex (Pc)) molecules. Interestingly, altering the Fmoc-FF/Pc molar ratios over a wide range cannot change the nanotubes structures according to transmission electron microscopy (TEM) and atomic force microscope (AFM) measurements. Although molecular dynamics simulations suggest that the noncovalent interactions between Fmoc-FF and Pc are quite weak, few Pc molecules can still change the secondary structures of a large number of Fmoc-FF assemblies, which hierarchically form helical supramolecular nanotubes with long-range ordered molecular packing, leading to intense CPL signals with large luminescence dissymmetry factor (g_lum  = 0.04). Consequently, the chiral reorganization of Fmoc-FF assemblies is dependent on the coassembly between Pc molecule and Fmoc-FF supramolecular architectures. These results open the possibility for the fine-tuning of helix and supramolecular nanotubes with CPL properties by using a small number of cofactors.

EQCM Analysis of the Insertion Phenomena in a n-Doped Poly-Alkyl-Terthiophene With Regioregular Pattern of Substitution

In the present work, we have undertaken the study of the n-doping process in poly-3,3″-didodecyl-2,2':5',2″-terthiophene (poly-33″-DDTT) employing the electrochemical quartz crystal microbalance (EQCM). The present study aims at understanding how cathodic charge in n-doped poly-33″-DDTT is compensated. For this purpose, the in situ analysis of the variations of the polymeric mass has been considered. Poly-33″-DDTT was obtained as a thin coating onto a metallic substrate via the anodic coupling of the corresponding monomer 3,3″-didodecyl-2,2':5',2″-terthiophene (33″-DDTT). When subjected to electrochemical n-doping in the polarization interval -2.5 ≤ E _appl ≤ 0 V vs. Ag/Ag⁺, the films of poly-33″-DDTT varied their mass according to a mechanism of cations insertion during n-doping and cations extraction during polymer neutralization. In fact, the electrochemical doping of polythiophenes requires the accompanying exchange of charged species to maintain the electroneutrality within the structure of the polymer in all states of polarization. At the end of a full electrochemical cycle (consisting of the n-doping and the successive neutralization of poly-33″-DDTT), the polymer retains a fraction of the mass acquired during n-doping, thus manifesting the phenomena of mass trapping. The combined analysis of electrochemical and microgravimetric data suggests that poly-33″-DDTT in the n-doped state undergoes (or electrocatalyzes) uncontrolled electrochemical reactions that are not accompanied by mass variations.

Self-Assembly and Circularly Polarized Luminescence from Achiral Pyrene-Adamantane Conjugates by Selective Inclusion with Cyclodextrins

The interaction between guest chromophores or lumiphores with host chiral cavity and their induced chirality is an important topic in supramolecular chemistry. Kodaka and Harata proposed a rule to explain the induced circular dichroism of the guest chromophores by host cyclodextrins. However, it remains unknown how a circularly polarized luminescence (CPL) signal will change when the lumiphores interacted with cyclodextrins in different modes. Here, we designed an achiral pyrene-adamantane conjugated guest molecule, N-(pyren-1-yl)adamantane-1-carboxamide (ACNP), and investigated its interactions with α/β/γ-cyclodextrins (CDs) and its induced CPL. Depending on the size match of the pyrene, adamantine with different cyclodextrins, distinct performance was observed. While α-CD could not induce a CPL signal of ACNP, β-CD could induce CPL in two modes, through adamantyl or direct pyrenyl induction, which could produce a CPL signal with opposite signs. γ-CD could always induce a negative CPL signal. Therefore, a rule of induced CPL of lumiphores by cyclodextrins can be proposed.

Chirality in polythiophenes: A review

Chiroptical polythiophene (PTh), as one of the most important chiral conductive polymers, is an emerging and hot topic in chiral materials, which shows great application potentials in fields as diverse as chiral sensing and separation, asymmetry catalysis, chiroptoelectronics, and even chiro-spintronics. This review summarizes progress in chiral polythiophenes (PThs) in the past 10 years, including the synthesis, properties and applications. Main focus is placed on the manner in which chirality is implemented and the optical activity of the chiral PThs. We showcase examples in which the chirality of PThs is induced by side chain substituents with point, planar, and axial chirality or arises from external chiral media. Application of chiral PThs is also included. Finally, perspectives for further development are offered.

Silica covering driven intensity enhancement and handedness inversion of the CPL signals of the supramolecular assemblies

Dipeptide-based hybrid materials with enhanced and inversed circularly polarized luminescence signals were fabricated through a dynamic supramolecular templating approach.