Amphiphile desymmetrisation-induced steric relief governs self-assembly pathways in aqueous media

Optimal Method to Realize Quantitative Detection of 1D and 2D Nanoassemblies Based on AIE-Active Bolaamphiphilic Molecules

Controllable transformation between the bolaamphiphilic molecule assemblies with different morphological nanostructures represents an exciting new direction for materials. However, there are still significant challenges for the quantitative detection and real-time monitoring of a controllable nanoself-assembly process due to insufficient measuring methods. Herein, we propose a new and effective fluorescence technology for realizing quantitative detection of a controllable conversion process of one-dimensional (1D)/two-dimensional (2D) nanoassemblies by introducing AIEgens as the fluorescence signal part. First, an aggregation-induced emission (AIE)-active bolaamphiphilic molecule (TPE-C8-Br) was designed and synthesized by incorporating tetraphenylethene (TPE) as the chromophore into the cationic amphiphile. Subsequently, the 1D nanofibrous morphology of TPE-C8-Br was successfully converted into the 2D rectangular and circular sheet of tosylate (TPE-C8-Ts) and sodium 1-hexanesulfonate (TPE-C8-HS) with the same molecular skeleton by the simple counterion change, respectively. Interestingly, all 2D nanoassemblies exhibited a stronger fluorescence sensitization effect than that of the 1D nanoassembly at the concentration above the critical micelle concentration (CMC) due to the higher degree of aggregation; thus, the rotation of the AIE-active TPE moiety is more restricted in TPE-C8-Ts and TPE-C8-HS. More meaningfully, a rather good linear correlation (FI = 3174.86 + 5282.29MP, R2 = 0.999) and a quadratic correlation (FI = 2113.71 + 5163.56MP - 2966.07MP2) were obtained between the molar percentage (MP) of the 2D nanoassembly and the fluorescence intensity (FI). The two proposed methods respond very well with regard to dependability, which can be used for the quantitative calculation of the molar ratio of 1D and 2D components in the controllable nanoself-assembly process. Therefore, this work offers an efficient and practical method for realizing the dynamic monitoring and quantitative detection of mutual conversion between different nanoassemblies.

Coaxial Helices in Chiral Supramolecular Aggregates from Highly Hindered Chiral Allenes

Chiral allenes self-assembly following a cooperative mechanism into a supramolecular chiral aggregate consisting of two coaxial helices: the internal helix described by the allene stack and the external helix which consist in a 4-helix described by the four allene substituents. More precisely, this supramolecular aggregate possesses six axially chiral elements within its structure-the allene, the allene stack (internal helix) and the stacks of the four allene substituents (external 4-helix)-. Interestingly, slight variations in the magnitude of the tilting degree while keeping its P- or M- orientation (internal helix) can vary the orientation of the 4-axial motifs at the external helix. Thus, while (P)-1 produces a supramolecular helix with a Θ ca. 15° (Pint) and a M1/P2/M1'/P2' orientation of the four axial motifs at the periphery, (P)-2 produces a supramolecular helix with a Θ ca. 23° (Pint) and a P1/P2/P1'/P2' orientation of the four axial motifs at the external helix. As a result, the ECD spectra and the AFM images of the (P)-1 and (P)-2 supramolecular aggregates dominated by the 1 and 1' substituents of the chiral allene indicate opposite handedness although the chirality of the building block and the orientation of the allene stack are the same.

Pyrrole βC-B-N Fused Porphyrins: Molecular Structures and Opto-Electrochemical Studies

Herein, we report the design, synthesis, structure, and electrochemical study of doubly βC-B-N fused Ni(II) porphyrins (1-trans, 1-cis, 2-trans, and 2-cis). These compounds have been synthesized from A2B2 type dipyridyl Ni(II) porphyrins (Ar=Ph for 1 a; Ar=C6F5 for 2 a) via Lewis base-directed electrophilic aromatic borylation reactions. The solution state structures of these compounds have been established using 1H NMR, 11B NMR, 1H-1H COSY, 1H-13C HSQC, and 19F-13C HSQC NMR techniques. Single crystal X-ray analysis have revealed that 1-trans, 1-cis, and 2-trans adopt ruffled conformations, with alternate meso-carbons on the opposite sides of the mean porphyrin plane. The Soret bands in the absorption spectra of the B-N fused molecules are ~40 nm redshifted compared to unfused Ni(II) porphyrin precursors. The B-N fusion have diminished the redox potential of fused porphyrins. Although 1-trans and 1-cis, show four oxidation processes, 2-trans and 2-cis show only three oxidation processes. DFT studies have revealed that the tetrahedral geometry of the boron has induced a twist in the π-conjugation, which destabilizes the HOMO and stabilizes the LUMO in 1-trans, 1-cis, 2-trans, and 2-cis.