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1.
Yuanting Su Dr. Xingyong Wang Yuantao Li Prof. You Song Yunxia Sui Prof. Xinping Wang 《Angewandte Chemie (International ed. in English)》2015,54(5):1634-1637
A series of bis[N,N‐di‐(4‐methoxylphenyl)amino]arene dications 1 2+– 3 2+ have been synthesized and characterized. Their electronic structures were investigated by various experiments assisted by theoretical calculations. It was found that they are singlets in the ground state and that their diradical character is dependent on the bridging moiety. 3 2+ has a smaller singlet–triplet energy gap and its excited triplet state is thermally readily accessible. The work provides a nitrogen analogue of Thiele’s hydrocarbon with considerable diradical character. 相似文献
2.
Cheng Zhang Samara MedinaRivero Wuyue Liu David Casanova Xiaozhang Zhu Juan Casado 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11413-11417
A tetracyano quinoidal tetrathiophene, having a central bi(thieno[3,4‐c]pyrrole‐4,6‐dione) acceptor, has been studied. The recovered aromaticity of the thiophenes produces a diradical species with cross‐conjugation between the inter‐dicyano and inter‐dione acceptor paths. A diradical character of y0=0.61 and a singlet–triplet gap of ?2.76 kcal mol?1 were determined. Competition between the two cross‐conjugated paths enhances the disjointed character of the SOMOs and results in the confinement of the diradical to the molecular center, enabling a thermodynamic diradical stabilization featuring a half‐life of 262 hours. Cross‐conjugation effects have been also addressed in the anionic species (up to a radical trianion). 相似文献
3.
Slavko Radenkovi? Svetlana Markovi? Ratko Ku? Nevena Stankovi? 《Monatshefte für Chemie / Chemical Monthly》2011,17(4):1013-1019
Abstract
An electronic structure study of singlet and triplet states of two series of polyacenequinododimethides was performed using the B3LYP method. It was found that the ground state of all examined polyacenequinododimethides is a singlet with significant diradical character. The diradical character of the compounds under investigation was estimated using the unrestricted symmetry-broken and complete active space methods. It was shown that polyacene-2,3-quinododimethides have more pronounced diradical character than polyacene-2,x-quinododimethides. The diradical character of polyacene-2,x-quinododimethides monotonically increases with their increasing molecular size. Within the series of polyacene-2,3-quinododimethides the diradical character is not a monotonic function of the number of hexagons. It was found that pentacene-2,3-quinododimethide has the most pronounced diradical character in this series. It can be predicted on the basis of the singlet–triplet gap values that even higher polyacenequinododimethides will be singlet, but not triplet molecules. 相似文献4.
Yong Ni Dr. Tullimilli Y. Gopalakrishna Dr. Hoa Phan Dr. Tun Seng Herng Shaofei Wu Yi Han Prof. Jun Ding Prof. Jishan Wu 《Angewandte Chemie (International ed. in English)》2018,57(31):9697-9701
Peri‐acenes are good model compounds for zigzag graphene nanoribbons, but their synthesis is extremely challenging owing to their intrinsic open‐shell diradical character. Now, the successful synthesis and isolation of a stable peri‐tetracene derivative PT‐2ClPh is reported; four 2,6‐dichlorophenyl groups are attached onto the most reactive sites along the zigzag edges. The structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It exhibits an open‐shell singlet ground state with a moderate diradical character (y0=51.5 % by calculation) and a small singlet–triplet gap (ΔES‐T=?2.5 kcal mol?1 by SQUID measurement). It displays global aromatic character, which is different from the smaller‐size bisanthene analogue BA‐CF3 . 相似文献
5.
Chao Chen Huapeng Ruan Zhongtao Feng Yong Fang Shuxuan Tang Yue Zhao Gengwen Tan Yuanting Su Xinping Wang 《Angewandte Chemie (International ed. in English)》2020,59(29):11794-11799
Although diradicals and azaacenes have been greatly attractive in fundamental chemistry and functional materials, the isolable diradical dianions of azaacenes are still unknown. Herein, we describe the first isolation of pyrene‐fused azaacene diradical dianion salts [(18‐c‐6)K(THF)2]+[(18‐c‐6)K]+? 1 2?.. and [(18‐c‐6)K(THF)]2+? 2 2?.. by reduction of the neutral pyrene‐fused azaacene derivatives 1 and 2 with excess potassium graphite in THF in the presence of 18‐crown‐6. Their electronic structures were investigated by various experiments, in conjunction with theoretical calculations. It was found that both dianions are open‐shell singlets in the ground state and their triplet states are thermally readily accessible owing to the small singlet–triplet energy gap. This work provides the first examples of crystalline diradical dianions of azaacenes with considerable diradical character. 相似文献
6.
Observation of a Thermally Accessible Triplet State Resulting from Rotation around a Main‐Group π Bond
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Arseni Kostenko Dr. Boris Tumanskii Dr. Miriam Karni Prof. Shigeyoshi Inoue Prof. Masaaki Ichinohe Prof. Akira Sekiguchi Prof. Yitzhak Apeloig 《Angewandte Chemie (International ed. in English)》2015,54(41):12144-12148
We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main‐group π bond, that is, the Si?Si double bond of tetrakis(di‐tert‐butylmethylsilyl)disilene ( 1 ). The highly twisted ground‐state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350–410 K. DFT‐calculated zero‐field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half‐field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet–triplet energy gap of only 7.3 kcal mol?1. 相似文献
7.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(45):14342-14346
Chichibabin's and Müller's hydrocarbons are classical open‐shell singlet diradicaloids but they are highly reactive. Herein we report the successful synthesis of their respective stable analogues, OxR‐2 and OxR‐3 , based on the newly developed oxindolyl radical. X‐ray crystallographic analysis on OxR‐2 reveals a planar quinoidal backbone similar to Chichibabin's hydrocarbon, in accordance with its small diradical character (y0=11.1 %) and large singlet–triplet gap (ΔES‐T=−10.8 kcal mol−1). Variable‐temperature NMR studies on OxR‐2 disclose a slow cis/trans isomerization process in solution through a diradical transition state, with a moderate energy barrier (ΔG≠298K=15–16 kcal mol−1). OxR‐3 exhibits a much larger diradical character (y0=80.6 %) and a smaller singlet–triplet gap (ΔES‐T=−3.5 kcal mol−1), and thus can be easily populated to paramagnetic triplet diradical. Our studies provide a new type of stable carbon‐centered monoradical and diradicaloid. 相似文献
8.
Ana Snchez‐Grande Jos I. Urgel Ale Cahlík Jos Santos Shayan Edalatmanesh Eider Rodríguez‐Snchez Koen Lauwaet Pingo Mutombo Dana Nachtigallov Reed Nieman Hans Lischka Bruno de la Torre Rodolfo Miranda Oliver Grning Nazario Martín Pavel Jelínek David cija 《Angewandte Chemie (International ed. in English)》2020,59(40):17594-17599
We report on the synthesis and characterization of atomically precise one‐dimensional diradical peripentacene polymers on a Au(111) surface. By means of high‐resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin‐flip inelastic excitations with an effective exchange coupling (Jeff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon‐based optoelectronics and spintronics. 相似文献
9.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(34):10317-10321
Tetrakis(trimethylsilyl)cyclobuta‐1,3‐diene ( 1 ) was subjected to a temperature‐dependent EPR study to allow the first spectroscopic observation of a triplet diradical state of a cyclobutadiene ( 2 ). From the temperature dependent EPR absorption area we derive a singlet→triplet ( 1 → 2 ) energy gap, E ST, of 13.9 kcal mol−1, in agreement with calculated values. The zero‐field splitting parameters D =0.171 cm−1, E =0 cm−1 are accurately reproduced by DFT calculations. The triplet diradical 2 is thermally accessible at moderate temperatures. It is not an intermediate in the thermal cycloreversion of cyclobutadiene to two acetylene molecules. 相似文献
10.
Dr. Anup Rana Yongseok Hong Dr. Tullimilli Y. Gopalakrishna Dr. Hoa Phan Dr. Tun Seng Herng Priya Yadav Prof. Jun Ding Prof. Dongho Kim Prof. Jishan Wu 《Angewandte Chemie (International ed. in English)》2018,57(38):12534-12537
The synthesis of a bithiophene‐bridged 34π conjugated aromatic expanded porphycene 1 and a cyclopentabithiophene bridged 32π conjugated anti‐aromatic expanded porphycene 2 by a McMurry coupling strategy is presented. Magnetic measurements and theoretical calculations reveal that both 1 and 2 exhibit an open‐shell singlet ground state with significant radical character (y0=0.63 for 1 ; y0=0.68, y1=0.18 for 2 ; y0: diradical character, y1: tetraradical character) and a small singlet–triplet energy gap (ΔES‐T=?3.25 kcal mol?1 for 1 and ΔES‐T=?0.92 kcal mol?1 for 2 ). Despite the open‐shell radical character, both compounds display exceptional stability under ambient air and light conditions owing to effective delocalization of unpaired electrons in the extended cyclic π‐conjugation pathway. 相似文献
11.
William T. G. Johnson David A. Hrovat Anne Skancke Weston Thatcher Borden 《Theoretical chemistry accounts》1999,102(1-6):207-225
Ab initio calculations on the lowest singlet and triplet states of 2,2-disilylcyclopentane-1,3-diyl find that the singlet
lies well below the triplet. The C
2 singlet diradical is calculated to be a minimum on the potential energy surface with an enthalpic barrier to ring closure
of ΔH
‡
298 = 13.5 kcal/mol at the CASPT2/6-31G* level of theory. The energy of the 1,3-divinyl-substituted singlet diradical is calculated
to be only 0.8 kcal/mol higher than that of 5,5-disilyl-1,3-divinylbicyclo[2.1.0]pentane at this level of theory, but the
transition state for their equilibration is computed to be 12.8 kcal/mol above the diradical in energy.
Received: 2 July 1998 / Accepted: 4 August 1998 / Published online: 16 November 1998 相似文献
12.
《中国化学》2018,36(6):487-490
Two‐electron oxidations of three 1,2‐di(bisphenylamino)‐benzenes afforded a class of nitrogen analogues of o‐quinodimethane. Their electronic structures in the ground state were studied by spectroscopic techniques including EPR and UV‐vis absorption spectroscopy. They have open‐shell singlet ground states with thermally accessible triplet states. One of them ( 1 2+) has been crystalized and isolated. SQUID measurements, single crystal X‐ray diffraction and theoretical calculations show 1 2+ has unexpected non‐Kekulé diradical character, sharply different from o‐quinodimethane. 相似文献
13.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(43):13669-13673
A stable 5,10‐bis(9‐fluorenylidene)porphyrin (Por‐Fl) diradicaloid was synthesized. It shows a quinoidal, saddle‐shaped geometry in the single crystal but can be thermally populated to a triplet diradical both in solution and in the solid state. Coordination with the Ni2+ ion (Por‐Fl‐Ni) does not significantly change the contorted conformation but reduces the singlet–triplet gap. Heat‐induced geometric change can explain the observed paramagnetic properties as well as unusual hysteresis in SQUID measurements. On the other hand, protonation (Por‐Fl‐2H+) dramatically changes the conformation while maintains the closed‐shell electronic structure. Our studies demonstrate how heat, coordination, and protonation affect the geometry, diradical character, and physical properties of conformationally flexible open‐shell singlet diradicaloids. 相似文献
14.
S. Markovi? S. Radenkovi? Z. Markovi? I. Gutman 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(13):2368-2372
The diradical character of zethrenes was investigated using a symmetry-broken UB3LYP/6-311G(d,p) method. The number of hexagons in the investigated molecules ranges from 6 to 12. It was found that all zethrenes are singlet
diradicals, whose diradical character increases with the increasing size of the molecules. A singlet diradical structure provides
a possibility for an electron pair to occupy different parts of space, and allows for achieving aromatic stabilization. It
can be predicted, on the basis of the singlet-triplet values, that even higher zethrenes will be singlet, but not triplet
molecules. 相似文献
15.
Ana Sánchez-Grande Dr. José I. Urgel Aleš Cahlík Dr. José Santos Shayan Edalatmanesh Eider Rodríguez-Sánchez Dr. Koen Lauwaet Dr. Pingo Mutombo Prof. Dana Nachtigallová Reed Nieman Prof. Hans Lischka Dr. Bruno de la Torre Prof. Rodolfo Miranda Dr. Oliver Gröning Prof. Nazario Martín Prof. Pavel Jelínek Prof. David Écija 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(40):17747-17752
We report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. Additionally, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S=0) singlet ground state. They are characterized by singlet–triplet spin-flip inelastic excitations with an effective exchange coupling (Jeff) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character which are potentially useful in carbon-based optoelectronics and spintronics. 相似文献
16.
Dr. Guangwu Li Dr. Tullimilli Y. Gopalakrishna Dr. Hoa Phan Dr. Tun Seng Herng Prof. Jun Ding Prof. Jishan Wu 《Angewandte Chemie (International ed. in English)》2018,57(24):7166-7170
A dithieno[a,h]‐s‐indacene‐ (DTI‐) based diradicaloid DTI‐2Br was synthesized and its open‐shell singlet diradical character was validated by magnetic measurements. On the other hand, its macrocyclic trimer DTI‐MC3 and tetramer DTI‐MC4 turned out to be closed‐shell compounds with global antiaromaticity, which was supported by X‐ray crystallographic analysis and NMR spectroscopy, assisted by ACID and 2D‐ICSS calculations. Such change can be explained by a subtle balance between two types of antiferromagnetic spin–spin coupling along the π‐conjugated macrocycles. The dications of DTI‐MC3 and DTI‐MC4 turned out to be open‐shell singlet diradical dications, with a singlet–triplet energy gap of ?2.90 and ?2.60 kcal mol?1, respectively. At the same time, they are both global aromatic. Our studies show that intramolecular spin–spin interactions play important roles on electronic properties of π‐conjugated macrocycles. 相似文献
17.
Jonathan D. Yuen Mingfeng Wang Jian Fan Dennis Sheberla Moureen Kemei Natalie Banerji Mariateresa Scarongella Sebastian Valouch Toan Pho Rajeev Kumar Eneida C. Chesnut Michael Bendikov Fred Wudl 《Journal of polymer science. Part A, Polymer chemistry》2015,53(2):287-293
The first observation that PBBTPD, a low bandgap, ambipolar conjugated donor-acceptor (DA) polymer based on benzobisthiadiazole (BBT), possesses an open-shell singlet ground state as well as a thermally accessible triplet state is described. Similarly, interesting electronic behavior in semiconducting organic DA oligomers based on BBT is also observed. Theoretical predictions have suggested that such behavior is due to the biradicaloid character of BBT and we provide experimental evidence indicating that these predictions are correct. Furthermore, the open shell character strengthens as the conjugation length increases, as observed in the BBT-based polymer, PBBTPD. We show that this biradicaloid structure is observed in each BBT moiety along the chain and that therefore PBBTPD is in fact a polyradicaloid. This observation will most likely aid in the development of better n-type polymeric acceptors for organic semiconductor applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 287–293 相似文献
18.
Dr. Qing Jiang Yi Han Ya Zou Dr. Hoa Phan Dr. Liu Yuan Dr. Tun Seng Herng Prof. Jun Ding Prof. Dr. Chunyan Chi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(67):15613-15622
Helicenes and extended helical π-conjugated compounds have been widely studied, but most of the systems contain only aromatic benzene or heterocyclic rings, showing local aromatic character. Herein, new S-shaped double [6]helicene 1 , which has two embedded para-quinodimethane (p-QDM) units, is reported. Due to the existence of a proaromatic quinoidal substructure, it has open-shell diradical character. Its model compound, C-shaped single [6]helicene 2 containing one p-QDM unit, was also synthesized and compared. Their ground-state structures and electronic properties were systematically studied by a combination of various experimental methods assisted by theoretical calculations. Compound 1 has a double-helical structure in the crystal, with the two terminal [6]helicene units bent in opposite directions (i.e., anti form). However, an anti/syn isomerization process with a moderate interconversion energy barrier was observed on the NMR timescale. Compound 1 shows amphoteric redox behavior. It also exhibits open-shell diradical character (y0=12.1 %) and a small singlet–triplet gap. On the other hand, compound 2 has a typical closed-shell nature. The dication and dianion of 1 also show open-shell diradical character. The dianion of 2 and the tetraanion of 1 exhibit similar electronic structures to their respective isoelectronic structures, that is, [6]helicene and a double [6]helicene. This work provides some insights into the design and synthesis of stable helical π systems with open-shell diradical character and magnetic activity. 相似文献
19.
Density functional theory and complete active space self-consistent field computations are applied to elucidate the singlet diradical character of square planar, diamagnetic nickel complexes that contain two bidentate ligands derived from o-catecholates, o-phenylenediamines, o-benzodithiolates, o-aminophenolates, and o-aminothiophenolates. In the density functional framework, the singlet diradical character is discussed within the broken symmetry formalism. The singlet-triplet energy gaps, the energy gained from symmetry breaking, the spin distribution in the lowest triplet state, and the form of the magnetic orbitals are applied as indicators for the singlet diradical character. Moreover, a new index for the diradical character is proposed that is based on symmetry breaking. All symmetry breaking criteria show that the complexes obtained from o-catecholates and o-benzodithiolates have the largest and the smallest singlet diradical character, respectively. The singlet diradical character should be intermediate for the complexes derived from o-phenylenediamines, o-aminophenolates, and o-aminothiophenolates. The diradical character of all complexes suggests the presence of Ni(II) central atoms. This is also indicated by the d-populations computed by means of the natural population analysis. 相似文献
20.
A Stable Trimethylenemethane Triplet Diradical Based on a Trimeric Porphyrin Fused π‐System
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Kenichi Kato Prof. Dr. Ko Furukawa Prof. Dr. Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2018,57(30):9491-9494
Trimethylenemethane (TMM) diradical is the simplest non‐Kekulé non‐disjoint molecule with the triplet ground state (ΔEST=+16.1 kcal mol?1) and is extremely reactive. It is a challenge to design and synthesize a stable TMM diradical with key properties, such as actual aliphatic TMM diradical centers and the triplet ground state with a large positive ΔEST value, since such species provide detailed information on the electronic structure of TMM diradical. Herein we report a TMM derivative, in which the TMM segment is fused with three NiII meso‐triarylporphyrins, that satisfies the above criteria. The diradical shows delocalized spin density on the propeller‐like porphyrin π‐network and the triplet ground state owing to the strong ferromagnetic interaction. Despite the apparent TMM structure, the diradical can be handled under ambient conditions and can be stored for months in the solid state, thus allowing its X‐ray diffraction structural analysis. 相似文献