Intramolecular Donor-acceptor Interactions Research Articles

Band-gap tuning of carbazole-containing donor–acceptor type conjugated polymers by acceptor moieties and π-spacer groups

Carbazole-containing donor–acceptor type conjugated polymers were prepared by Sonogashira cross-coupling reaction of 3,6-diethynyl-9-hexadecylcarbazole and arylene dibromides, and the optical and electrochemical properties were extensively investigated. Copolymerization with 4,7-dibromo-2,1,3-benzothiadiazole furnished the orange-colored polymer with a charge-transfer band at 440nm in CH2Cl2, indicating efficient intramolecular donor–acceptor interactions. On the other hand, the color of the copolymer with 2,5-dibromopyridine was ocher and the longest wavelength absorption band was 381nm in CH2Cl2, suggesting almost negligible donor–acceptor interactions. This difference was also reflected by the emission spectra, solvatochromic behaviors, and electrochemical redox potentials. Comparison of the ethynylene spacer between the donor and acceptor moieties to other π-spacers revealed that the ethynylene spacer serves as a more efficient π-spacer than vinylene and direct connection (without spacer) for strong donor–acceptor coupling in this polymer system.

Zipper-featured delta-peptide foldamers driven by donor--acceptor interaction. Design, synthesis, and characterization.

Donor-acceptor interaction between electron-rich 1,5-dioxynaphthalene (DAN) and electron-deficient pyromellitic diimide (PDI) has been utilized to induce the formation of a new kind of zipper-featured delta-peptide foldamers. Seven l-ornithine-based delta-peptides 1a-g, in which one to three DNA and PDI units are incorporated to the two ends of the peptide backbones, respectively, have been designed and prepared by the standard liquid-phase synthetic method. (1)H NMR, UV-vis, and fluorescent quenching studies reveal that all the delta-peptides adopt folding conformations in nonpolar chloroform and polar DMF as a result of intramolecular donor-acceptor interaction between the DAN and PDI units. The folding states become more compact for the peptide skeletons possessing more donor-acceptor interacting sites. Variable-temperature UV-vis experiments indicate that, although the folding is a dynamic process, the folding state can remain even at 150 degrees C in DMF. Circular dichroism (CD) investigations reveal that the new generation of delta-peptides have similar folding patterns. A zipper-featured folding motif has been proposed for the new generation of delta-peptide foldamers. Molecular modeling has generated two most stable folding states for the longest delta-peptide 1g, with an energy difference of 26.80 kcal/mol.

Ate complexes of Ge(II) and Sn(II) with bidentate ligands [LiE 14(OCH 2CH 2NMe 2) 3] 2 (E 14=Ge, Sn): synthesis and structure

The reaction of equimolar quantities of LiOCH 2CH 2NMe 2 and E 14(OCH 2CH 2NMe 2) 2 (E 14=Ge, Sn) in ether yielded new ate complexes [LiE 14(OCH 2CH 2NMe 2) 3] 2 (E 14=Ge ( 1), Sn ( 2)) with bidentate ligands. The compounds 1 and 2 are white crystalline substances which are highly soluble in THF and pyridine and very sensitive to the traces of oxygen and moisture. The structures of these compounds are studied by X-ray diffraction analysis. The ate complexes 1 and 2 are powerful nucleophiles and may be employed as ligands (neutral) in the coordination chemistry of the transition metals. The electronegative O-substituents at the divalent E 14 atoms render them less oxidizable than alkyl- or aryl-substituted derivatives, and the bidentate ligands, owing to intramolecular donor–acceptor interactions, make them more thermodynamically stable compared to monodentate ligands.

Conformationally controlled intramolecular charge transfer complexes.

Trans-1-acceptor-2-donor-substituted cyclohexanes (1), as well as their 4- (or 5-)methyl-substituted homologues (2), have been prepared and are shown to form intramolecular charge-transfer (donor-acceptor) complexes. These weak complexes are turned on and off by the chair-chair interconversion of the cyclohexane ring. The CT absorptions have been measured and the equilibrium constants for the ring reversal have been determined by UV/vis spectroscopy at 298 K, as well as by NMR spectroscopy at two temperatures: at 183 K, by direct comparison of signals due to the two chair conformations, and at 300 K, by comparison of calculated and measured widths of the alpha-proton signals. The Gibbs free energies assigned to the donor-acceptor interactions range between 0 and -1 kcal mol(-1). A crystal structure of one of the complexes (1b) confirms the intramolecular donor-acceptor alignment and interaction. The regioisomers of the methyl-substituted complexes were characterized by NOE interaction between the methyl and an alpha-proton cis to it.

1H,117 Sn J‐HMBC spectroscopy as a tool for the determination of long‐range nJ (1H,117Sn) coupling constants in the investigation of intramolecular donor–acceptor interaction in [2‐(N,N‐dimethylaminomethyl)phenyl]stannanes

Abstract1H, 117Sn J‐HMBC spectroscopy was implemented as a tool for the determination of long range nJ(1H, 117Sn) coupling constants of [2‐(N,N‐dimethylaminomethyl)phenyl]stannanes, ArR1R2R3Sn or Ar2R1R2Sn, where R1, R2 and R3 are Ph or n‐Bu, and/or Cl or Br. It is demonstrated that coupling constants which are too small to be measured from multiplet splittings in the 1H or 117Sn spectra can be measured from the development of the sine modulation of the intensity of the 1H, 117Sn HMBC correlation peaks as a function of the incremented preparation time of the 1H,117Sn HMBC pulse sequence. It is examined whether such couplings can be used as straightforward indicators for the existence of intramolecular nitrogen–tin interactions. While some coupling constants are shown to depend on the strength of the above‐mentioned interaction, it is also demonstrated that 6J(1H,117Sn) coupling constants between the N‐methyl groups and the tin nucleus can be observed even in structures where no nitrogen–tin interactions are possible. Copyright © 2001 John Wiley & Sons, Ltd.

1,3-Diaxial Repulsionvs.π-Delocalization in the 7-Amino-2,4-diazabicyclo[3.3.1]nonan-3-one Skeleton

(1R,5S,6S,8R)-6,8,9-Trihydroxy-3-oxo-2,4-diazabicyclo[3.3.1]nonan-7-ammonium chloride hydrate (3Cl⋅H2O) and (1R,5S,6S,8R)-7-amino-6,8,9-trihydroxy-2,4-diazabicyclo[3.3.1]nonan-3-one (4) have been prepared, and their crystal structures have been determined from single-crystal X-ray diffraction data. Both compounds consist of a bicyclic skeleton with the three N-atoms in an all-cis-1,3,5-triaxial arrangement. Considerable repulsion between these axial N-atoms is indicated by a significant distortion of the two cyclohexane chairs and by increased N⋅⋅⋅N distances. The lone pair of the free amino group of 4 is involved in intermolecular H-bonding and is turned away from the adjacent carbonyl C-atom of the urea moiety. The structural properties together with the observed reactivity do not provide any evidence for an intramolecular donor-acceptor interaction between the carbonyl C- and the amine N-atom.

Formation of Gallium-Nitrogen Rings and Cages by Inter- and Intramolecular Donor Acceptor Interactions

We have recently started to systematically investigate main group model compounds with donor and acceptor centres in geminal position to one another.1 The compounds characterised so far include E-O-N, E-N-N and E-C-N systems (E = Si, Ge, Sn), with the E-O-N and E-N-N moieties forming intramolecular E⋯N interactions.

Intramolecular Phototransfer of Protons and the Quenching of Fluorescence of Derivatives of 2-(Coumarinyl-3)-5-(ortho-hydroxyphenyl)-1,3,4-oxadiazole

The spectral-luminescence properties of ortho-hydroxy derivatives of 2-(coumarinyl-3)-5-phenyl-1,3,4-oxadiazole have been studied. It is shown that the basic reason for the decreased quantum yield of emission for the compounds studied is the high-speed phototransfer of a proton (estimated as ∼109 s-1). Fluorescence of the products of this reaction (phototautomers) was not observed. It was confirmed by quantum-chemical calculations that the increase in efficiency of nonradiative dissipation of the electron excitation energy in phototautomeric forms of ortho-hydroxycoumarinyloxadiazoles is explained by an increase in intramolecular donor-acceptor interaction on introduction of the coumarin unit into the molecule. As a result of the high efficiency of nonradiative deactivation of the excited state, the ortho-hydroxyderivatives studied have promise as UV photostabilizers in polymeric materials.

Insights into the Staudinger Reaction: Experimental and Theoretical Studies on the Stabilization of cis-Phosphazides

The Staudinger-model reaction H3P (1) + HN3 (2) → H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N–N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis -3is 8.2 kcal mol−1 more stable than trans -3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor–acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.

Insights into the Staudinger Reaction: Experimental and Theoretical Studies on the Stabilization ofcis-Phosphazides

The Staudinger-model reaction H3P (1) + HN3 (2) → H3P=NH (5) + N2 (6) has been investigated at the CCSD(T)/6-31G**//MP2(Full)/6-31G* level. Primary products formed in this reaction are the phosphazides H3P=N–N=NH (3) which exist as trans and cis isomers. In contrast to some previous assumptions, cis -3is 8.2 kcal mol−1 more stable than trans -3 but decomposes rather easily into the expected products H3P=NH and N2. This decomposition can be effectively hampered by intramolecular donor–acceptor interactions as shown by calculations on model compounds as well as by experiments. Thus the reaction of a methylene-σ3,λ3-phosphanyl-σ5,λ5-phosphorane with PhN3 led to a new four-membered heterocycle containing a thermally remarkable stable cis-phosphazide moiety.

Fluorescence and aggregation behavior of a polyimide in solutions

The UV-visible absorption and fluorescence spectra of a soluble polyimide, YS-30, in several organic solvents were measured over a wide range of concentration. The experimental results show that there exist both intramolecular and intermolecular electron donor acceptor interactions for YS-30 molecules. The fluorescence behavior of YS-30 in N,N-dimethylacetamide and in chloroform solutions is similar in general, except that its ground-state intermolecular charge transfer emission is more obvious in N,N-dimethylacetamide solution. This difference is attributed to the greater extent of disruption of the chain packing by solvent or/and the more efficient radiationless energy dissipation process from the excited state complexes to chloroform. The intensity ratio of intermolecular charge transfer emission to intramolecular charge transfer emission is used to characterize the state of aggregation of YS-30 molecules in solutions. The plot of this ratio versus concentration indicates the existence of two critical concentrations. It is also found from the same plot that the decrease of coil size is very pronounced during the initial stage of shrinkage.

Hyper-Rayleigh scattering studies of an ionic species Solvent effect on hyperpolarizability of 1-anilinonaphthalene-8-sulfonic acid ammonium salt

The hyperpolarizability β of an ionic species, 1-anilinonaphthalene-8-sulfonic acid ammonium salt (ANS), was determined in various solvents by the Hyper-Rayleigh scattering (HRS) technique. Increase in the solvent polarity led to a decrease in the hyperpolarizability; i.e. β=37.4±2.5×10 -30 esu in p-dioxane and β=10.3±1.3×10 -30 esu in water. The solvent effect was explained by considering the dissociation ratio of the sulfonic acid ammonium group in solution, which influences the intramolecular donor–acceptor interaction between phenylamino and sulfonic acid ammonium groups.

Donor–acceptor substituted tetraethynylethenes

A comprehensive series of donor/acceptor substituted tetraethynylethenes has been prepared by palladium‐catalyzed acetylenic coupling. The conjugated C‐atom scaffolds of these remarkably stable compounds are planar, including the substituted phenyl rings. Trends in electronic, optical, and structural properties as a function of degree and pattern of substitution are reported and the effectiveness of intramolecular donor–acceptor interactions via linear conjugation paths and cross‐conjugation paths compared.

Intramolecular coordination at phosphorus: donor-acceptor interaction in three- and four-coordinated phosphorus compounds

The phosphorus derivatives P(X)(O 2C 6H 4−1,2) 2[C 6H 4(CH 2NMe 2) 2−2] ( 9–11) undergo ready extension of coordination by N → P intramolecular donor-acceptor interaction as shown by 31P NMR and dynamic 1H NMR spectroscopy. This extension of coordination does not occur with P(X)(OEt) 2[C 6H 4(CH 2NMe 2) 2−2] ( 7 and 8). The ΔG ≡ of pseudo-rotation was calculated by dynamic 1H NMR spectroscopy to be 57–58 kJ mol −1 for the three compounds P(X)O 2C 6 4−1,2) 2[C 10H 6(NMe 2−8)] ( 19–21).

Verbindungen mit dem 5,6-Benzo-l,3,2-diazaphosphorinan-4-on-Ringsystem: Synthese von 2-Chlor-, 2-N,N-dimethylamino-und 2-Bis-(2-chlorethyl)amino- substituierten Derivaten mit drei-und vierfach koordiniertem Phosphor / Compounds Involving the 5,6-Benzo-l,3,2-diazaphosphorinane-4-one Ring System: Synthesis of 2-Chloro-, 2-N,N-dimethylamino-and 2-Bis-(2-chloroethyl)amino- Substituted Derivatives with Three-and Four-Coordinated Phosphorus

The reaction of methylisatoic anhydride with 2-(aminomethyl)pyridine, 3-(aminomethyl)- pyridine, 3-dimethylamino-1-propylamine, 3-diethylamino-1-propylamine and 3-dibutylamino- 1-propylamine furnished the N-substituted N'-methylanthranilic amides 1-5. In the reaction of 1-5 with phosphorus trichloride the 3-substituted 5,6-benzo-1-m ethyl-1,3,2-diazaphosphorinane- 4-one derivatives 6 to 10 were obtained. The possibility of intramolecular donoracceptor interaction between the nitrogen atom of the R2N group and the λ3P atom is suggested on the basis of 1H NMR studies. The reaction of 9 with dimethylamino-trimethylsilane furnished the 2-dimethylamino-substituted product 11. In the reaction of 6, 7 and 10 with bis-(2-chloroethyl)amine hydrochloride/triethylamine the expected substitution products 12 to 14 were obtained. 5,6-Benzo-2-[bis-(2-chloroethyl)amino]-1-methyl-3-(3-picolyl)-1,3,2-diazaphosphorinan- 4-one 13 reacted with (COD)PtCl2 to give the czs-dichloro-platinum(II) complex 15. The characterisation of 1-15 is based on the 1H-, 13C-, and 31P-NMR spectra, mass spectra and X-ray structure determinations of the precursor compounds 1 and 3

PHOSPHONIUMHALOGENIDE MIT DER N,N′,N′-TRIMETHYLETHYLENDIAMINGRUPPIERUNG

Abstract The reaction of the alkyl- and aryl- substituted halophosphonium halides 2 and 4 with N-trimethylsilyl-N,N′,N′-trimethylethylenediamine 1 furnished compounds 3 and 5. No intramolecular donor-acceptor interaction between the nitrogen atom of the NMe2 grouping and phosphorus was observed by 1H NMR spectroscopy. There was no reaction of triisopropyl- and tris-diethylamino-substituted halophosphonium halides with compound 1. Attempts to exchange the halide anion in 3 and 5 by the non-coordinating [BPh4]− anion, possibly inducing intramolecular Me2N → P coordination, failed.

Das 7,8-Benzo-5-chloro-1,4,4-trimethyl-1-aza-4-azonia-6,9-dioxa-5 λ5-phosphaspiro[4.4]nonanyl-Kation: Röntgenstrukturanalyse und temperaturabhängige 1H-NMR-Spektren: The 7, 8-Benzo-5-chloro-1,4,4-trimethyl-1-aza-4-azonia-6,9-dioxa-5 λ).5-phosphaspiro[4.4]nonanyl Cation: X-Ray Crystal Structure Determination and Variable 1H NMR Spectra

The 1H NMR spectrum of the spirophosphorane 3 at room temperature indicates dynamic behaviour of the cation. The low-temperature 1H NMR spectra of 3 exhibit two sets of doublets for the protons of the diastereotopic N(CH3)2 groups. The free enthalpy of activation for the dynamic process was determined (58.6 KJ/mole). In the reaction of 3 with sodium tetraphenylborate the crystalline compound, 4, involving the non-coordinating anion, [B(C6H5)4]-, was obtained. The X-ray crystal structure analysis of 4 reveals the presence of a five-membered ring, formally as a result of intramolecular donor-acceptor interaction between the nitrogen atom of the N(CH3)2 group and phosphorus. The geometry at phosphorus deviates somewhat from ideal trigonal bipyramidal.

N,N′,N′-Trimethylethylendiamin-substituierte Phosphor(III)-Verbindungen und deren Oxidation zu Derivaten mit tetra- und pentakoordiniertem Phosphor / N,N′,N′-Trim ethylethylenediamine-Substituted Phosphorus(III) Com pounds and their Oxidation to Derivatives with Four-and Five-Coordinated Phosphorus

A study was made of the intramolecular donor-acceptor interaction in N,N′,N′-trimethylethylenediamine- substituted phosphorus compounds, involving λ3-, λ4- and λ5-phosphorus atoms, as a function of the nature of the substituents at phosphorus. The reaction of N-trimethylsilyl-N,N′,N′-trimethylethylenediamine (1) with (PriO)2PCl furnished the acyclic, trimethylethylenediamine-substituted phosphorus(III) compound 4. There is no NMR spectroscopic evidence for an intramolecular donor-acceptor interaction between the phosphorus atom and the nitrogen atom of the dimethylamino group in 4. The oxidation of the trivalent phosphorus atom in 4 and in the related compound 5 by sulfur, selenium, tetrachloroo- benzoquinone, and hexafluoroacetone led to the corresponding λ4P compounds 6 - 9 and to the λ5P compounds 10 and 11. No intramolecular donor-acceptor interaction could be detected in any of these products. There was no reaction between 5 and elemental tellurium. The reaction products were characterized by NMR spectroscopy, mass spectrometry, and by elemental analysis.

Synthesis and crystal structure of the mixed lithium sodium guanidide [Li 4Na 2{NC(NMe 2) 2} 6]: A stack of three (metal-nitrogen) 2 dimeric rings with additional intramolecular (tertiary amine) nitrogen-lithium coordinations

The tetralithium disodium guanidide [Li 4Na 2{NC(NMe 2) 2} 6], crystallized from a 1 : 1 : 2 Bu nLi : Bu nNa : HNC(NMe 2) 2 mixture, has been studied by X-ray crystallography and found to be related to the ketimide [Li 4Na 2{NC(Ph)Bu t} 6], reported earlier as having a stacked-core of three (metal-nitrogen) 2 ring dimers with Li + and Na + cations in end rings and the central ring, respectively. However, it also displays a unique feature : intramolecular donor-acceptor interactions which connect dimethylaminonitrogen atoms project from the central ring to Li + cations in the end rings. Although these interactions are long range (average length 2.304 Å, cf. 2.139 Å for LiN core bonds), they still significantly influence the core bonding as evidenced by an analysis of bond lengths and bond angles.

Structures of Tris(donor)‐Tris(acceptor)‐Substituted Benzenes, 1. Steric, Polar and Hydrogen‐Bonding Effects in Triaminotrinitrobenzenes

AbstractThe X‐ray analyses of three 1,3,5‐tris(alkylamino)‐2,4,6‐trinitrobenzenes (alkyl = iPr, neopentyl, tBu; 1d – f) show their benzene rings to be highly distorted towards boat (1d iPrNH2) and twist‐boat (1e,f) forms. The patterns found for intramolecular donor‐acceptor interaction and hydrogen bonding depend on the conformation of the benzene core: boat structures have the “stern” amino group strongly donating to the “bow” nitro group in the para position and two stronger hydrogen bonds between the substituents on the “side” of the boat, whereas twist‐boat structures have two amino groups strongly interacting with the nitro group in their common ortho position to which there are also two strong hydrogen bonds. 1d – f undergo conformational exchange on the 13C‐NMR time scale at room temperature. Cooling to 220 K allows detection of all carbon signals and shows C1 symmetry to be present. AM1 calculations reproduce the distortions of 1d – f. Computations on several 2,4,6‐tridonor‐substituted 1,3,5‐trinitrobenzenes indicate that the pronounced deviations from planarity in 1a – f originate largely from electronic effects.