Abstract:Molecularly-defined cyclic azobenzene oligomers were prepared and chain-length and topology-dependent on photoresponsive properties were investigated.
“…The photoisomerization of a series of macrocyclic oligomers containing azobenzene moiety in the main chain and their linear analogs was studied by Zhu and co-workers [ 266 ] (Scheme 24 ). Tetraethylene glycol (TEG) was chosen as the building block for the preparation of amphiphilic polymers of good solubility.…”
Section: Polymers Bearing Macrocycle(s) and Azo Motif(s)mentioning
confidence: 99%
“… Scheme 24 The synthesis of the molecularly-defined linear 201 and cyclic oligomers 202 (n = 1–6) [ 266 ] …”
Section: Polymers Bearing Macrocycle(s) and Azo Motif(s)mentioning
Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans–cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds’ structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed.
“…The photoisomerization of a series of macrocyclic oligomers containing azobenzene moiety in the main chain and their linear analogs was studied by Zhu and co-workers [ 266 ] (Scheme 24 ). Tetraethylene glycol (TEG) was chosen as the building block for the preparation of amphiphilic polymers of good solubility.…”
Section: Polymers Bearing Macrocycle(s) and Azo Motif(s)mentioning
confidence: 99%
“… Scheme 24 The synthesis of the molecularly-defined linear 201 and cyclic oligomers 202 (n = 1–6) [ 266 ] …”
Section: Polymers Bearing Macrocycle(s) and Azo Motif(s)mentioning
Azobenzene derivatives due to their photo- and electroactive properties are an important group of compounds finding applications in diverse fields. Due to the possibility of controlling the trans–cis isomerization, azo-bearing structures are ideal building blocks for development of e.g. nanomaterials, smart polymers, molecular containers, photoswitches, and sensors. Important role play also macrocyclic compounds well known for their interesting binding properties. In this article selected macrocyclic compounds bearing azo group(s) are comprehensively described. Here, the relationship between compounds’ structure and their properties (as e.g. ability to guest complexation, supramolecular structure formation, switching and motion) is reviewed.
“…When building discrete oligomers, the efficient orthogonal chain terminal deprotections, together with end‐to‐end coupling reaction, are highly desirable for a high degree of polymerization (DP) and scalable preparation. A number of coupling reactions, such as Suzuki coupling, Sonogashira, Stille, Buchwald, Wittig, copper catalyzed azide–alkyne cycloaddition (CuAAC), and Glaser coupling reactions, as well as esterification, amidation, and etherification, have been utilized in precision synthesis of oligomers. Among them, metal‐catalyzed coupling reactions are frequently used owing to their versatility, effectiveness, and sometimes “click‐like” manner .…”
Orthogonal maleimide and thiol deprotections were combined with thiol-maleimide coupling to synthesizediscrete oligomers/macromolecules on ag ram scale with molecular weights up to 27.4 kDa (128mer,7 .9 g) using an iterative exponential growth strategy with ad egree of polymerization (DP) of 2 n À1. Using the same chemistry,a"readable" sequence-defined oligomer and ad iscrete cyclic topology were also created. Furthermore,u niform dendrons were fabricated using sequential growth (DP = 2 n À1) or double exponential dendrimer growth approaches (DP = 2 2 n À1) with significantly accelerated growth rates.Aversatile,efficient, and metal-free method for construction of discrete oligomers with tailored structures and ah igh growth rate would greatly facilitate researchi nto the structure-property relationships of sophisticated polymeric materials.Itiswell-documented that the property/function of polymers strongly relies on molecular weight (MW), topology and sequence distribution. [1] Nature creates av ariety of biopolymers,s uch as DNA [2] and proteins, [3] with precisely defined chain lengths,f unctional sequences,a nd topologies.S ince most artificial polymers are polydisperse with various chemical structures and MWs at the molecular level, the research on structure-property relationship is mainly limited to ambiguous or statistical evaluation methods. [4] Therefore,i t is of great interest for the synthesis of discrete oligomers with uniform chain lengths (that is,am onodisperse MW), monomer unit sequences,a nd topologies,t oa dvance more comprehensive and accurate study of the structure-property relationships of polymers. [5] Driven by this challenge,chemists have made numerous efforts to synthesize discrete oligomers utilizing diverse approaches.Within these pioneering works, [6] iterative sequential, [7] or exponential [8] growth through terminal deprotections/transformations and end-to-end couplings, [9] is commonly used for preparation of discrete oligomers.W henb uilding discrete oligomers,t he efficient orthogonal chain terminal deprotections,t ogether with endto-end coupling reaction, are highly desirable for ah igh degree of polymerization (DP) and scalable preparation. A number of coupling reactions,s uch as Suzuki coupling, [8b] Sonogashira, [9a] Stille, [9b] Buchwald, [8e] Wittig, [9c] copper catalyzed azide-alkyne cycloaddition (CuAAC), [8d, i, k, l] and Glaser coupling reactions, [10] as well as esterification, [11] amidation, [9d] and etherification, [8c, 9e] have been utilized in precision synthesis of oligomers.A mong them, metal-catalyzed coupling reactions are frequently used owing to their versatility, effectiveness,a nd sometimes "click-like" manner. [7g, 8d, i, k] However,m etal ions may accumulate after many cycles and thereby contaminate target products.This circumstance might yield inaccurate measurements when investigating the structure-property relationships of the discrete oligomerslimiting their potential for future applications.Herein, for the first time,wecombined orthogo...
“…Star-shaped azos are also different from linear or cyclic azo n -mers with the same number of azo-fragments (trimers, tetramers, etc.). First of all, this is manifested in different supramolecular structures the stars and the linear or cyclic [11] n -mers can build. Moreover, the branching results in lower melting temperatures, and lower viscosity [6,12,13], meaning that these properties are topology-dependent.…”
In this paper, the columnar supramolecular aggregates of photosensitive star-shaped azobenzenes with benzene-1,3,5-tricarboxamide core and azobenzene arms are analyzed theoretically by applying a combination of computer simulation techniques. Without a light stimulus, the azobenzene arms adopt the trans-state and build one-dimensional columns of stacked molecules during the first stage of the noncovalent association. These columnar aggregates represent the structural elements of more complex experimentally observed morphologies—fibers, spheres, gels, and others. Here, we determine the most favorable mutual orientations of the trans-stars in the stack in terms of (i) the π–π distance between the cores lengthwise the aggregate, (ii) the lateral displacements due to slippage and (iii) the rotation promoting the helical twist and chirality of the aggregate. To this end, we calculate the binding energy diagrams using density functional theory. The model predictions are further compared with available experimental data. The intermolecular forces responsible for the stability of the stacks in crystals are quantified using Hirshfeld surface analysis. Finally, to characterize the self-assembly mechanism of the stars in solution, we calculate the hydrogen bond lengths, the normalized dipole moments and the binding energies as functions of the columnar length. For this, molecular dynamics trajectories are analyzed. Finally, we conclude about the cooperative nature of the self-assembly of star-shaped azobenzenes with benzene-1,3,5-tricarboxamide core in aqueous solution.
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