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Theory Study and Present CT Trend of Organic Charge Transfer Complexes
Published in Atsushi Nagai, Koji Takagi, Conjugated Objects, 2017
Atsushi Nagai, Daniel J. Siegwart
Recently organic complexes with electron donor (D) and electron acceptor (A) moieties have emerged as promising candidates for advanced mechanochromic materials due to their intramolecular CT capability This endows the materials with charge ordering, spin density waves (SDWs), spin‐Peierls ground state, and superconductivity 17 Aromatic molecules, such as coronene, are typical examples of π‐electron systems able to donate electrons, depending on their ionization potential I. As a typical example, 7,7,8,8‐tetracyanoquinodimethane (TCNQ) can be easily reduced to form the open‐shell electron radical anion TCN Q when it comes into contact with electron donors. Recently a three‐component system comprising two differentbenzenoid hydrocarbons together with one molecule of TCNQ was reported.18 The pyreneTCNQ complex was synthesized with a molecular ratio of 1:1 in toluene under refluxing conditions. Notably the compound crystallized in a monoclinic system, with a space group of P21/n with half of the molecules of pyrene and TCNQ as the asymmetric part of the unit cell. The pyrene moiety is tilted with respect to the TCNQ along the stacks, with an angle between mean planes of 6o (Fig. 14.2). If this principle could be introduced into an oligomer ore polymer chain backbone, a force‐ sensitive CT complex as the chemical unit (mechanophore) would be linked into the polymer and oligomer backbones. Mechanical loading would then drive conversion of the mechanophore to a new chemical species. Therefore, we expect the possibility of completely alternating stacking for the CT complex between pyrene and TCNQ using mechanical grinding. This is to say the mechanochromism 19 phenomenon will be observed, which is characterized by changes in color (absorption) and/or luminescence as a result of mechanical grinding or pressing of a sample in the solid state. Accordingly the mechanical grinding of pyreneTCNQ complexes in the solid state would lead to a much higher increase of high CT complex absorption and the color of the grinded solid will change. To create the system described above utilized the simple structure of squaramide, which is typically synthesized via the stepwise reaction of commercially available squaric acid with amines and aromatic amines.20 The hydrogen bond donoracceptor properties of squaramide have attracted interest for various applications in supramolecular chemistry for example, as catalysts21, molecular sensors, 22 and in molecular recognition as receptors for charged guests.23 Moreover there is a growing number of bioactive squaramides involved in cancerous,24 inflammatory25 and infectious26 diseases, among others.
Synthesis, structure and properties of luminescent Cd(II) coordination polymers based on imidazole-decorated tetraphenylethylene
Published in Journal of Coordination Chemistry, 2021
Zou-Hong Xu, Shu-Man Zhao, Yue Zhao, Wei-Yin Sun
Coordination polymers (CPs) are inorganic-organic hybrid materials constructed by linkage of metal ions or clusters with organic linkers [1]. Over the last two decades, CPs have attracted attention because of their potential applications in gas storage and separation [2], heterogeneous catalysis [3], molecule storage and conversion [4], etc. In particular, there is increasing interest in the development of luminescent CPs for optoelectronic devices, fluorescent sensors and biomedical imaging due to tunability of luminescence [5]. Varied luminescent CPs have been constructed and the ones with d10 metal centers and conjugated organic ligands are candidates for photoluminescence [6]. As for organic ligands, aggregation-induced emission (AIE) chromophores, for example tetraphenylethylene (TPE) and its derivatives, can be used as building blocks for construction of CPs, and enhanced fluorescence can be expected [7]. TPE derivatives are excellent chromism materials and CPs with TPE derivatives will have abundant florescent properties, such as photochromism [8], solvatochromism [9], thermochromism [10], mechanochromism [7, 11], etc. Mechanochromism essentially is a color change triggered by mechanical stimulations such as grinding, compressing and shearing [12]. Such behavior is usually accompanied by a phase transition including the changes of molecular arrangements in the packing modes, aggregation states and intermolecular interactions [13]. The mechanochromism of organic TPE derivatives has been widely explored, however, mechanical stimulation remains unexplored for CPs.