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1.
A series of triarylboranes, in which different substituents are introduced at the para position of the dimethylamino group of a 2‐dimesitylboryl‐2’‐(N,N‐dimethylamino)biphenyl core unit, have been comprehensively investigated to explore the effect of structural modification on photophysical properties. The introduction of electron‐accepting substituents would facilitate the HOMO→LUMO charge transfer (CT) transition. In contrast, the intramolecular CT transition is significantly prohibited when electron‐donating substituents are incorporated. Notably, the HOMO→LUMO CT transition mainly consists of the transition from the electron‐donating amino group to an electron acceptor other than boryl when a strong electron acceptor such as the dicyanovinyl group is present. This dicyanovinyl‐substituted compound displays sensing abilities to discriminate fluoride and cyanide ions. In solution in THF, the fluoride ions first bind to the boron center, then attack the α‐carbon atom of the dicyanovinyl group, whereas the cyanide anion acts on the electron‐accepting centers in the reverse sequence. As a result, the absorption and emission change in different manners upon addition of fluoride and cyanide ions.  相似文献   

2.
The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core.  相似文献   

3.
Electron‐donating molecules play an important role in the development of organic solar cells. (Z )‐2‐(2‐Phenylhydrazinylidene)acenaphthen‐1(2H )‐one (PDAK), C18H12N2O, was synthesized by a Schiff base reaction. The crystal structure shows that the molecules are planar and are linked together forming `face‐to‐face' assemblies held together by intermolecular C—H…O, π–π and C—H…π interactions. PDAK exhibits a broadband UV–Vis absorption (200–648 nm) and a low HOMO–LUMO energy gap (1.91 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital), while fluorescence quenching experiments provide evidence for electron transfer from the excited state of PDAK to C60. This suggests that the title molecule may be a suitable donor for use in organic solar cells.  相似文献   

4.
Thermal reactions of hitherto α‐(3‐pyridyl)‐N‐phenylnitrone ( 1 ) with mono‐substituted electron‐rich and electron‐neutral dipolarophiles are regio‐, and stereo‐selective (exo‐selective), controlled by LUMO ‐ dipole ‐ HOMO‐ dipolarophile interaction, and furnish syn‐5‐substituted‐3‐(3‐pyridyl)‐isoxazolidines ( 5 ) in high yields. With electron deficient dipolarophiles such as acrylonitrile there is observed a loss of regioselectivity as well as stereoselectivity and the regioselectivity is reversed in reactions with methyl vinyl ketone and methyl acrylate, due to intervention of HOMO‐dipole ‐ LUMO‐dipolarophile interaction, affording 4‐substi‐tuted‐3‐(3‐pyridyl)‐isoxazolidines ( 7 ) as major products. Reactions of nitrone ( 1 ) with disubstituted dipolarophiles such as methyl methacrylate and ethyl coronate furnish methyl syn‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐5‐carboxylate ( 8 ) and ethyl anti‐5‐methy‐3‐pyridyl‐1‐phenyl‐isoxazolidine‐4‐carboxylate ( 10 ), respectively, in high yields. Reaction with N‐Phenylmaleimide affords novel isoxazolidino‐pyrro‐lidinediones bearing a 3‐pyridyl moiety ( 11, 12 ). A mechanistic rationalization of the obtained results in terms of electronic, steric and secondary interactions is proffered.  相似文献   

5.
The molecular structure of the title salt, C11H17N4+·H2PO4, has been determined from single‐crystal X‐ray analysis and compared with the structure calculated by density functional theory (DFT) at the BLYP level. The crystal packing in the title compound is stabilized primarily by intermolecular N—H...O, O—H...N and O—H...O hydrogen bonds and π–π stacking interactions, and thus a three‐dimensional supramolecular honeycomb network consisting of R42(10), R44(14) and R44(24) ring motifs is established. The HOMO–LUMO energy gap (1.338 eV; HOMO is the highest occupied molecular orbital and LUMO is the lowest unoccupied molecular orbital) indicates a high chemical reactivity for the title compound.  相似文献   

6.
The electron positive boron atom usually does not contribute to the frontier orbitals for several lower‐lying electronic transitions, and thus is ideal to serve as a hub for the spiro linker of light‐emitting molecules, such that the electron donor (HOMO) and acceptor (LUMO) moieties can be spatially separated with orthogonal orientation. On this basis, we prepared a series of novel boron complexes bearing electron deficient pyridyl pyrrolide and electron donating phenylcarbazolyl fragments or triphenylamine. The new boron complexes show strong solvent‐polarity dependent charge‐transfer emission accompanied by a small, non‐negligible normal emission. The slim orbital overlap between HOMO and LUMO and hence the lack of electron correlation lead to a significant reduction of the energy gap between the lowest lying singlet and triplet excited states (ΔET‐S) and thereby the generation of thermally activated delay fluorescence (TADF).  相似文献   

7.
In 3,4‐di‐2‐pyridyl‐1,2,5‐oxadiazole (dpo), C12H8N4O, each mol­ecule resides on a twofold axis and inter­acts with eight neighbours via four C—H⋯N and four C—H⋯O inter­actions to generate a three‐dimensional hydrogen‐bonded architecture. In the perchlorate analogue, 2‐[3‐(2‐pyrid­yl)‐1,2,5‐oxadiazol‐4‐yl]pyridinium perchlorate, C12H9N4O+·ClO4 or [Hdpo]ClO4, the [Hdpo]+ cation is bisected by a crystallographic mirror plane, and the additional H atom in the cation is shared by the two pyridyl N atoms to form a symmetrical intra­molecular N⋯H⋯N hydrogen bond. The cations and perchlorate anions are linked through C—H⋯O hydrogen bonds and π–π stacking inter­actions to form one‐dimensional tubes along the b‐axis direction.  相似文献   

8.
In the title compound, (C10H9NOS6)K[Hg(SCN)4] or (EDT–TTF–CONHMe)K[Hg(SCN)4)], fully oxidized organic (EDT–TTF–CONHMe) radical cations form quasi‐one‐dimensional stacks running along the monoclinic 21 axis and alternating along the crystallographic [101] direction with inorganic anion stacks made from mixed K+–[Hg(SCN)4]2− ribbons. For each anion, three essentially collinear SCN ligands inter­act with the K+ ions via short N⋯K contacts, while the terminal N atom of the fourth SCN group is engaged in a number of hydrogen‐bond contacts with the –CH, –NH and –CH2 hydrogen‐bond donors of the amide function. Radical cations are dimerized along the stacks and the crystal conductivity is activated.  相似文献   

9.
The structure of trans‐3‐(3‐pyridyl)acrylic acid, C8H7NO2, (I), possesses a two‐dimensional hydrogen‐bonded array of supramolecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring molecules [3.821 (1) Å] along the a axis. The crystal structure of the photoproduct, rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride, C16H16N2O42+·2Cl, (II), consists of a three‐dimensional hydrogen‐bonded network built from crosslinking of helical chains integrated by self‐assembly of dipyridinium cations and Cl anions via different O—H...Cl, C—H...Cl and N+—H...Cl hydrogen‐bond interactions.  相似文献   

10.
The polycarbazoles have been proved to efficiently suppress the keto defect emission. Three carbazole‐based conjugated polymers, poly[9‐methyl‐3‐(4‐vinylstyryl)‐9H‐carbazole] (PBC), poly[9‐methyl‐3‐(2‐(5‐vinylthiophen‐2‐yl)vinyl)‐9H‐carbazole] (PBT) and poly[9‐methyl‐3‐(2‐(5‐vinylfuran‐2‐yl)vinyl)‐9H‐carbazole] (PBF), were investigated by quantum‐chemical techniques, and gain a detailed understanding of the influence of carbazole units and the introduction of electron‐donating on the electronic and optical properties. The electronic properties of the neutral molecules, HOMO‐LUMO gaps (ΔE), in addition to ionization potential (Ip) and electron affinity (Ea), are studied using B3LYP density functional theory. The lowest excitation energies (Eg) and the absorption wavelength are studied using the time dependent density functional theory (TDDFT). The calculated results show that all three series of polymers have good planarity. And the highest‐occupied molecular orbital (HOMO) energies lift about 0.36–0.61 eV and thus the IP decrease about 0.01–0.19 eV compared to polycarbazole, suggesting the significant improved hole‐accepting and transporting abilities. By introducing the electron‐donating 1,4‐divinylphenylene or 2,5‐divinylthiophene or 2,5‐divinylfuran units in the backbone, and the lowest‐unoccupied molecular orbital (LUMO) energies decrease 0.20–0.39 eV. In addition, PBC, PBT and PBF have longer maximal absorption wavelengths than polycarbazole. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 706–714, 2009  相似文献   

11.
A series of N‐methyl‐3,4‐fulleropyrrolidine (NMFP) derivatives were designed by selecting different π‐conjugated linkers and electron‐donating groups as D‐π‐A and D‐A systems. The optimised structures and photo‐physical properties of NMFP and its derivatives have been determined using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods with the B3LYP functional and the 6‐31G basis set. According to the computation analysis, both the π‐conjugated linkers and the electron‐donating groups can influence the electronic and photo‐physical properties of the NMFP derivatives. Our calculated results demonstrated that the electron‐donating groups, with significant electron‐donating ability, had the tendency to increase the highest occupied molecular orbital (HOMO) energy. The π‐conjugated linkers with lower resonance energy decreased the lowest occupied molecular orbital (LUMO) energy and caused a significant decrease in the energy gap (Eg) between the EHOMO and ELUMO. A Natural Bond Orbital (NBO) analysis examines the effect of the electron‐donating group, π conjugated linker, and electron‐withdrawing group for these NMFP derivatives. For the NMFP derivatives, a projected density of state (PDOS) analysis demonstrated that the electron density of HOMO and LUMO are concentrated on the electron‐donating group and the π‐conjugated linker, respectively. A TD‐DFT/B3LYP calculation was performed to calculate the electronic absorption spectra of these NMFP derivatives. Both the electron‐donating group and the π‐conjugated linker contribute to the major absorption peaks, which are assigned as HOMO to LUMO transitions and are red‐shifted relative to those of non‐substituted NMFP.  相似文献   

12.
The crystal structures of two salts, products of the reactions between [(5‐methyl‐2‐pyridyl)aminomethylene]bis(phosphonic acid) and 4‐aminopyridine or ammonia, namely bis(4‐aminopyridinium) hydrogen [(5‐methyl‐2‐pyridinio)aminomethylene]diphosphonate 2.4‐hydrate, 2C5H7N2+·C7H10N2O6P22−·2.4H2O, (I), and triammonium hydrogen [(5‐methyl‐2‐pyridyl)aminomethylene]diphosphonate monohydrate, 3NH4+·C7H9N2O6P23−·H2O, (II), have been determined. In (I), the Z configuration of the ring N—C and amino N—H bonds of the bisphosphonate dianion with respect to the Cring—Namino bond is consistent with that of the parent zwitterion. Removing the H atom from the pyridyl N atom results in the opposite E configuration of the bisphosphonate trianion in (II). Compound (I) exhibits a three‐dimensional hydrogen‐bonded network, in which 4‐aminopyridinium cations and water molecules are joined to ribbons composed of anionic dimers linked by O—H...O and N—H...O hydrogen bonds. The supramolecular motif resulting from a combination of these three interactions is a common phenomenon in crystals of all of the Z‐isomeric zwitterions of 4‐ and 5‐substituted (2‐pyridylaminomethylene)bis(phosphonic acid)s studied to date. In (II), ammonium cations and water molecules are linked to chains of trianions, resulting in the formation of double layers.  相似文献   

13.
Bis‐silylated and bis‐germylated derivatives of Lu3N@Ih‐C80 ( 3 , 4 , 5 ) were successfully synthesized by the photochemical addition of disiliranes 1 a , 1 b or digermirane 2 , and fully characterized by spectroscopic, electrochemical, and theoretical studies. Interestingly, digermirane 2 reacts more efficiently than disiliranes 1 a and 1 b because of its good electron‐donor properties and lower steric hindrance around the Ge?Ge bond. The 1,4‐adduct structures of 3 , 4 , 5 were unequivocally established by single‐crystal X‐ray crystallographic analyses. The electrochemical and theoretical studies reveal that the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the 1,4‐adducts are remarkably smaller than those of Lu3N@Ih‐C80, because the electron‐donating groups effectively raise the HOMO levels. It is also observed that germyl groups are slightly more electron‐donating than the silyl groups on the basis of the redox properties and the HOMO–LUMO energies of 4 and 5 . Bis‐silylation and bis‐germylation are effective and versatile methods for tuning the electronic characteristics of endohedral metallofullerenes.  相似文献   

14.
Reactions of the title free‐base porphyrin compound (TPyP) with dysprosium trinitrate hexahydrate in different crystallization environments yielded two solid products, viz. [μ‐5,15‐bis(pyridin‐1‐ium‐4‐yl)‐10,20‐di‐4‐pyridylporphyrin]bis[aquatetranitratodysprosium(III)] benzene solvate, [Dy2(NO3)8(C40H28N8)(H2O)2]·C6H6, (I), and 5,10,15,20‐tetrakis(pyridin‐1‐ium‐4‐yl)porphyrin pentaaquadinitratodysprosate(III) pentanitrate diethanol solvate dihydrate, (C40H30N8)[Dy(NO3)2(H2O)5](NO3)5·2C2H6O·2H2O, (II). Compound (I) represents a 2:1 metal–porphyrin coordinated complex, which lies across a centre of inversion. Two trans‐related pyridyl groups are involved in Dy coordination. The two other pyridyl substituents are protonated and involved in intermolecular hydrogen bonding along with the metal‐coordinated water and nitrate ligands. Compound (II) represents an extended hydrogen‐bonded assembly between the tetrakis(pyridin‐1‐ium‐4‐yl)porphyrin tetracation, the [Dy(NO3)2(H2O)5]+ cation and the free nitrate ions, as well as the ethanol and water solvent molecules. This report provides the first structural characterization of the exocyclic dysprosium complex with tetrapyridylporphyrin. It also demonstrates that charge balance can be readily achieved by protonation of the peripheral pyridyl functions, which then enhances their capacity in hydrogen bonding as H‐atom donors rather than H‐atom acceptors.  相似文献   

15.
The ground geometrical and electronic structures, charge transfer (CT) behaviors, absorption, and emission properties of the three copper(I) complexes [Cu(pypz)(POP)]+ (1) , [Cu(pympz)(POP)]+ (2) , and [Cu(pytfmpz)(POP)]+ (3) (pypz=1‐(2‐pyridyl)pyrazole, pympz=3‐methyl‐1‐(2‐pyridyl)pyrazole, and pytfmpz=3‐trifluoromethyl‐1‐(2‐pyridyl)pyrazole), have been investigated using density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT). The vertical absorption energies of the all copper(I) complexes are well reproduced by TD‐DFT calculations based on the CT amount calculations. The triplet emission properties of the all copper(I) complexes were correctly evaluated at BMK/LANL2DZ/6‐31G* level of theory. In addition, the thermally activated delayed fluorescence properties of 1–3 were discussed in detail based on the spatial separation of the HOMO and LUMO and vertical excited energies. These theoretical insights should be expected to provide some guides for the design and synthesis of efficient luminescent copper(I) complexes. © 2014 Wiley Periodicals, Inc.  相似文献   

16.
A series of trisbenzothieno[1,2:7,8:13,14]hexa‐peri‐hexabenzocoronenes were synthesized and characterized by a combination of NMR, 2D NMR, MALDI‐TOF MS, UV/Vis absorption spectroscopy, and 2D‐WAXS measurement. By structural modulation like decoration of electro‐donating alkoxyl chain, and conversion from an electron‐rich thiophene ring into an electron‐poor thiophene‐S,S‐dioxide moiety, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the hexabenzocoronenes derivatives can be effectively tuned which is further verified by the DFT calculations and cyclic voltammetry.  相似文献   

17.
Assembling two quadruply bonded dimolybdenum units [Mo2(DAniF)3]+ (DAniF=N,N′‐di(p‐anisyl)formamidinate) with 1,4‐naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2(DAniF)3}2(μ‐1,4‐O2CC10H6CO2)], [{Mo2(DAniF)3}2(μ‐1,4‐OSCC10H6COS)], and [{Mo2(DAniF)3}2(μ‐1,4‐S2CC10H6CS2)]. In the X‐ray structures, the naphthalene bridge deviates from the plane defined by the two Mo?Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed‐valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab=258–345 cm?1) are lowered by a factor of two or more, and the electron‐transfer rate constants (ket≈1011 s?1) are reduced by about one order of magnitude. These results show that, when the electron‐transporting ability of the bridge and electron‐donating (electron‐accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO–LUMO energy gap by elevating the (bridging) ligand‐based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.  相似文献   

18.
Three new organic semiconductors, in which either two methoxy units are directly linked to a dibenzotetrathiafulvalene (DB‐TTF) central core and a 2,1,3‐chalcogendiazole is fused on the one side, or four methoxy groups are linked to the DB‐TTF, have been synthesised as active materials for organic field‐effect transistors (OFETs). Their electrochemical behaviour, electronic absorption and fluorescence emission as well as photoinduced intramolecular charge transfer were studied. The electron‐withdrawing 2,1,3‐chalcogendiazole unit significantly affects the electronic properties of these semiconductors, lowering both the HOMO and LUMO energy levels and hence increasing the stability of the semiconducting material. The solution‐processed single‐crystal transistors exhibit high performance with a hole mobility up to 0.04 cm2 V?1 s?1 as well as good ambient stability.  相似文献   

19.
[26]Hexaphyrin(1.1.1.1.1.1) bearing two 5‐formyl‐2‐pyrrolyl groups at the 5‐ and 20‐positions was prepared by cross‐condensation of 5,10‐bis(pentafluorophenyl)‐substituted tripyrrane with 2,5‐diformylpyrrole as an effective binuclear metal‐coordinating ligand, owing to the two hemiporphyrin‐like NNNN pockets. In fact, metalation of this hexaphyrin with ZnII, CuII, and PdII salts proceed smoothly at room temperature to give the corresponding bismetal complexes that displayed remarkably redshifted absorption spectra reaching deep into near infrared region. These redshifted absorption bands are ascribed, through electrochemical investigations and DFT calculations, to two structural motifs: the N‐metalopyrrole substructure that elevates the HOMO level due to the electron‐donating property and the two coordinated metal ions that serve as Lewis acids to lower the LUMO level.  相似文献   

20.
A series of tetrathiafulvalene (TTF)‐annulated porphyrins, and their corresponding ZnII complexes, have been synthesized. Detailed electrochemical, photophysical, and theoretical studies reveal the effects of intramolecular charge‐transfer transitions that originate from the TTF fragments to the macrocyclic core. The incremental synthetic addition of TTF moieties to the porphyrin core makes the species more susceptible to these charge‐transfer (CT) effects as evidenced by spectroscopic studies. On the other hand, regular positive shifts in the reduction signals are seen in the square‐wave voltammograms as the number of TTF subunits increases. Structural studies that involve the tetrakis‐substituted TTF–porphyrin (both free‐base and ZnII complex) reveal only modest deviations from planarity. The effect of TTF substitution is thus ascribed to electronic overlap between annulated TTF subunits rather than steric effects. The directly linked thiafulvalene subunits function as both π acceptors as well as σ donors. Whereas σ donation accounts for the substituent‐dependent charge‐transfer transitions, it is the π‐acceptor nature of the appended tetrathiafulvalene groups that dominates the redox chemistry. Interactions between the subunits are also reflected in the square‐wave voltammograms. In the case of the free‐base derivatives that bear multiple TTF subunits, the neighboring TTF units, as well as the TTF ? + generated through one‐electron oxidation, can interact with each other; this gives rise to multiple signals in the square‐wave voltammograms. On the other hand, after metalation, the electronic communication between the separate TTF moieties becomes restricted and they act as separate redox centers under conditions of oxidation. Thus only two signals, which correspond to TTF . + and TTF2+, are observed. The reduction potentials are also seen to shift towards more negative values after metalation, a finding that is considered to reflect an increased HOMO–LUMO gap. To probe the excited‐state dynamics and internal CT character, transient absorption spectral studies were performed. These analyses revealed that all the TTF–porphyrins of this study display relatively short excited‐state lifetimes, which range from 1 to 20 ps. This reflects a very fast decay to the ground state and is consistent with the proposed intramolecular charge‐transfer effects inferred from the ground‐state studies. Complementary DFT calculations provide a mechanistic rationale for the electron flow within the TTF–porphyrins and support the proposed intramolecular charge‐transfer interactions and π‐acceptor effects.  相似文献   

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