The mysterious "triangle power" -- terpenes

Triangulene is a new kind of three line ground state condensed ring compound Among them, the simplest all hydrocarbon trigone is supposed to be composed of 22 carbon atoms fused by six groups of six membered rings It was predicted to exist as early as the 1950s but never synthesized Triangle structure is generally recognized as a stable structure in mechanics, but in the field of chemistry, it is not necessarily a stable chemical structure The stability of trigonene is not very good, because it contains two unpaired covalent electrons, which is easy to oxidize and has very high activity Nature Nanotechnology chemistry is a discipline that constantly explores new fields and new substances Chemists are always challenging the impossible to synthesize chemicals with special properties There have been previous studies on the synthesis of substituted triazenes, while the problem of the synthesis of unsubstituted "pure" triazenes has now been solved Niko pavli qiek of IBM Research Center in Switzerland, etc through scanning tunneling electron microscopy and atomic force microscopy (STM / AFM) technology, they used surface synthesis method to obtain unsubstituted trigonene, and characterized this molecule, and finally "saw" the existence of trigonene This research result is published on Nature Nanotechnology Because triarylene is easy to oxidize, the general synthesis route is difficult to succeed The team used the opposite strategy, using subtraction instead of the usual addition Dihydrotriangulene, a precursor compound, has two more hydrogen atoms than triangulene and can combine with two unpaired electrons of triangulene to improve the structural stability And then they try to get rid of the two hydrogen, and they get the trigone The research team placed the precursor compounds (2a, 2b) of dihydrotriazene on the surface of Cu (111), NaCl (100) and Xe (111), and then "cut" two hydrogen atoms and create unpaired electrons at the atomic level by applying two consecutive voltage pulses with STM / AFM microscope probes The synthesis of trigonene (source: Nature Nanotechnology), while other scientists have invested a lot of energy in the introduction of heteroatoms in the center of trigonene, by adjusting its molecular structure and physical properties to explore its new potential Takuji HATAKEYAMA group of chemistry department, Kansai University, Japan, published an article on angew Chem Int ed., reporting their new progress in the synthesis of 4,8,12-triazene diversity at heteroatom center, including the preparation of nitrogen-containing macrocyclic precursor and the introduction of central heteroatom via electrophilic c-li bond and C-H bond substitution reaction The researchers also found that they are bowl like three-dimensional structures, which are different from those with phosphorus or silicon as the center Representative triazenes and their synthesis strategies (source: Angew Chem Int Ed.) the figure above shows some representative heteroatom triangles and their synthesis strategies For example, boron centered trigonene D is a good core framework of electron transport materials, which can be used in organic light-emitting diodes and disk liquid crystals with bipolar carrier transport characteristics; phosphorus centered trigonene E can be used to package fullerenes due to its bowl shaped structure The traditional strategies of building heteroatom center triarylene include: 1 The aromatic rings around triarylamine, triaryphosphine, triarylboron are connected by funk reaction; 2 The aromatic nucleophilic substitution reaction of snar type However, the limitation of these methods is that the bridging atoms are only limited to carbon, oxygen and sulfur In order to solve this problem, the author first synthesized the nitrogen-containing macrocyclic precursor 1, then lithium-halide exchange and nucleophilic attack on electrophilic reagents such as boron, phosphorus and silicon, introduced heteroatoms, and finally constructed six membered rings respectively through the substitution reaction of C-H bond to obtain 4,8 of heteroatom center, This strategy has the characteristics of universality and diversity In short, the previous strategies are all from the inside out, first introducing heteroatoms and then forming a ring on the outside; in this paper, from the outside to the inside, first synthesizing a large ring precursor, then introducing a heteroatom center to guide the subsequent formation of a ring The synthesis of TOT derivatives (source: nature) and other scientists have made efforts to further understand the unique properties of triazenes Trioxytriangulene (TOT) is a kind of neutral π radical with delocalized single electron occupied orbit (SOMO) Professor Morita's research group from Aichi University of technology in Japan designed and synthesized two kinds of TOT derivatives with substituents, and found that this organic intermediate radical is as stable as ordinary organic molecules In addition, the team of Professor Nakai Haoji from Waseda University, who cooperates with him, explained the mechanism of the unusual near-infrared absorption characteristics of the crystal polymer through quantum chemical calculation Through the study of the magnetic properties of neutral radicals 2 and 3, it is found that both of them can exist stably in air at room temperature, either in solid state or in solution state The researchers found that the high chemical stability originated from the delocalization of unpaired electrons in π - electron system There is a broad absorption band at 1134 nm and 1488 nm, respectively, and this absorption band can only be observed along the direction of the crystal column in their single crystal polarization reflection spectrum These anisotropic reflectance spectra clearly show that the long wave absorption bands of 2 and 3 are due to the π - π interaction in the solid state In order to overcome the huge computational problems caused by free radicals and polymers in quantum chemistry, Professor Nakai has developed divide and conquer, The calculation method of DC) greatly reduces the amount of calculation, and the quantum chemical calculation of multiple molecular aggregates can be carried out by extracting some column stacking structures (up to 60 molecules and 4380 atoms) The calculation shows that with the increase of the number of stacking molecules, the absorption wavelength is gradually red shifted When the number reaches a certain value, the wavelength is close to the experimental near-infrared absorption wavelength, thus the optical absorption spectrum observed in the experiment is well reproduced In addition, the calculation also shows that due to the stacking of 2 and 3 into one-dimensional columnar structure, the electronic orbits of different molecules overlap It is this strong interaction between molecules that causes the unusual absorption of near-infrared light The excitation diagram (source: nature) summarizes the existing research achievements in the field of triazene, including the synthesis of the most "pure" Triazene, the synthesis of new hybrid Triazene derivatives, and the in-depth study of the unique properties of triazene Its unique structure has the application potential in many fields The next task is not only to open the "brain hole", but also to synthesize more new structural trigonenes The research on their unique properties and applications should be further deepened It can be imagined that one day, we will unveil this mysterious "triangle power" and conquer it completely.