Dimethoxynaphthalene Research Articles

Ninhydrin as a building block in scaffold-linked chromophoric dyad construction

The reaction of ninhydrin with ester-activated cyclobutene epoxide (CE-1) containing the fused 1,4- dimethoxynaphthalene ( DMN ) chromophore, gave adducts formed by 1,3-dipolar cycloaddition at the central (C 2)-CO (major) and the outer (C 1,3 )-CO (minor) positions. Conversion of the minor adduct to quinoxalines ( QIN ) by reaction with o-phenylenediamines at the α-dione moiety, albeit in poor yield, led to spiro-DMN-1,4 σ σ σ σ-QIN dyad in which the plane of the chromophore was orthogonally orientated yet angled to the plane of the DMN chromophore. Reaction of ninhydrin with o-phenylenediamines yielded the corresponding 11-oxoindeno(1,2-b)quinoxalines which were coupled with CE-BLOCKs to form spiro adducts by reaction at the carbonyl site; the product from CE -1 was identical with that formed above. Another class of spiro-fused dyads was produced by reaction of ninhydrin with a primary amine followed by cycloaddition of CE-BLOCKs at the carbonyl site, where the amine was available to deliver one chromophore and the CE-BLOCK another.

ChemInform Abstract: Total Synthesis of Angucyclines. Part 13. Biomimetic-Type Approach to a Potential Precursor of the Landomycinone Angucyclinone.

Abstract The dimethoxy naphthalene derivative 10 with two vicinal side chains was prepared by reaction of the dibromide 7 with silyl ether 8 ([Bu4N][Ph3SnF2]-catalysis) followed by Stille reaction of 9 with stannane 5. Acidic hydrolysis gave the triketo ester 11 that cyclized in a biomimetic-type reaction to the highly substituted dihydro benz[a]anthracene 12, a potential precursor of the angucyclinone landomycinone.

Intramolecular interactions and photoinduced electron transfer in isoalloxazine-naphthalene bichromophores

The synthesis, the structural characterization and electrochemical and photophysical properties of new linear ( OFn) and macrocyclic ( MFn) bichromophoric systems containing one flavin and one naphthalene moiety, separated by (CH 2) n alkyl chains ( n = 4 or 6), are reported. The electrochemical properties of OF4, OF6, MF4, MF6 were investigated by cyclic voltammetry (CV) in ultra-dry THF and compared with the model compounds containing either the flavin unit ( FL6) or the monomethoxy- ( mona) and dimethoxy naphthalene ( dmona) derivatives, respectively. While only minor ground-state interactions were evidenced between the chromophores in the voltammetric curves and absorption spectra of bichromophores, luminescence data evidenced intramolecular photoinduced electron transfer processes as main deactivation routes of flavin-centered excited states. The rates of the intramolecular photoinduced electron transfer, involving the oxynaphthalene moieties as electron donors, were finally determined.

New approach for evaluation optical absorption measurements of charge transfer complexes between dimethoxynaphthalenes and tetracyanoethylene: singular value decomposition method

Singular-value decomposition (SVD) method is a numerical multidimensional technique appropriate for evaluation of optical absorption measurements of 1:1 charge transfer complexes (CTCs). Matrix algebra of the absorption data for different solutions and wavenumbers is primarily used for evaluation of the equilibrium constant and to obtain some general expressions to illustrate physical significance of the results obtained. The influence of the ratio of the concentrations of donor and acceptor is examined. It can lead to information about the stoichiometry of the complex formed in solution. Calculations on data for CTCs between dimethoxynaphthalene (DMNs) and tetracyanoethylene (TCNE) in CH 2Cl 2 at various temperatures are described. The results suggest that there is a noticeable difference in the K 4, caused by substitutions at α- and β-positions, because the α-position of naphthalene exhibits relatively high electron density compared with the corresponding β-position. There is a linear correlation between the donor HOMO energy and charge-transfer absorption maxima.

Time-Resolved EPR Study on Reorganization Energies for Charge Recombination Processes in Nanometer-Separated Radical Ion Pairs

The reorganization energies for the intermolecular charge recombination processes have been determined for the electron donor-acceptor systems involving the quinones and methoxy aromatic molecules by time-resolved EPR andcyclic voltammetry measurements in polar solvents. We have carefully examined what distance between the donor and acceptor molecules is effective for the radical pair mechanism (RPM) chemically induced dynamic electron polarization (CIDEP) detection using the stochastic Liouville equation on the basis of the charge transfer (CT) interaction mechanism in the singlet-triplet energy splitting (2J) in radical ion pairs. The RPM CIDEP shows that the signs of the J are inverted from positive to negative with decreasing temperature. The results are interpreted by the CT interaction mechanism. With the observations of the J ∼ 0 condition, the individual values of the total and solvent reorganization energies (As) are determined for several 1.2 nm separated donor-acceptor systems. The individual As values ranging from 1.27 to 1.39 eV in the present donor-acceptor systems agree with those calculated from the Marcus continuum dielectric model at 1.2 nm donor-acceptor separation within the deviation of ∼0.1 eV. In the dimethoxynaphthalene (DMN)-duroquinone (DQ) system, the solvent reorganization around the methoxy groups is dominated due to the localization of the electron spin density in the DMN cation radical.

A Time-Dependent Density Functional Study of the Singlet−Triplet Energy Gap in Charge-Separated States of Rigid Bichromophoric Molecules

Time-dependent density functional theory (TD-DFT) has been used to calculate gas-phase singlet−triplet energy gaps, ΔEST, for the charge-separated states of a series of donor−[bridge]−acceptor molecules, in which a dimethoxynaphthalene (DMN) donor and a dicyanovinyl (DCV) acceptor are connected by a rigid hydrocarbon (norbornylogous) bridge, ranging from four bonds to 13 bonds in length. Through the use of five different functionals, B3P86, B3LYP, B3PW91, BPW91, and BLYP, together with the 6-311G(d) basis set, it is found that TD-DFT theory gives a good description of the electron density distribution in the charge-separated (CS) states in that the calculated dipole moments of the CS states are in acceptable agreement with experimental data. The calculated ΔEST values for all members of the donor−[bridge]−acceptor series are positive (i.e., the singlet CS state lies higher in energy than the triplet CS state), and the distance dependence of ΔEST follows an exponential decay with increasing number, n, of b...

Photophysics of novel donor–{saturated rigid hydrocarbon bridge}–acceptor systems exhibiting efficient excitation energy transfer

Intramolecular singlet–singlet energy transfer is reported in a series of novel donor–{saturated rigid hydrocarbon bridge}–acceptor (D–B–A) molecules containing dimethoxynaphthalene (DMN) or dimethoxybenzene (DMB) as the energy donor chromophore, and a dione group as the acceptor. In the case of the DMN donor, the efficiency of energy transfer has been studied as a function of the bridge length with the number of sigma bonds linking the donor and acceptor groups ranging from 6 to 12. Highly efficient energy transfer is observed in all the D–B–A molecules studied, and the results are discussed with reference to the role of dipole–dipole and through-bond donor–acceptor coupling mechanisms. The energy transfer process facilitates efficient photosensitized decomposition of the dione moiety. These results are compared to data published on related donor–acceptor compounds. The chemical structure of the backbone linking the donor and acceptor is shown to have a marked effect on the photophysics of the molecules.

Solvent-Mediated Intramolecular Electron Transfer in U-Shaped Systems with Different “Bite Sizes”

The rate of photoinduced charge separation is measured as a function of solvent for four donor (D)−bridge−acceptor (A) systems: DMN[10]DCV, DMN[10nb]DCV, DMN[10cy]DCV, and DMAN[10cy]DCV. In the first three members of this series, the D/A pair is kept constant and contains the strong dimethoxynaphthalene (DMN) donor which enables detection of electron transfer over a wide range of solvent polarity. In the fourth member, DMN is substituted by a dimethoxyanthracene (DMAN) unit, which decreases the driving force for photoinduced charge separation by about 0.58 eV and thereby limits the occurrence of electron transfer to polar solvents. In all systems the bridge is held at a length of 10 σ bonds. The configuration of the bridge is, however, varied to increase its bending in the series, which leads to center-to-center D/A distances decreasing from 13.4 Å in the first system to 9.54 Å in the second, and 7.50 Å in the latter two. In DMN[10nb]DCV, the rate of intramolecular charge separation over 9.54 Å is always smaller than that over 13.4 Å in DMN[10]DCV, which is in line with a dominant through-bond mechanism that is more efficient via an extended array of σ bonds. However, in DMN[10cy]DCV, the rate is as high as or even higher than that in DMN[10]DCV. Although changes in the driving force are also important, as shown, for example, by the dramatic rate decrease in DMAN[10cy]DCV as compared to that of DMN[10cy]DCV, the high rates observed for DMN[10cy]DCV in polar aromatic solvents as well as in acetonitrile strongly indicate an important contribution of through-solvent interaction across the 7.5 Å D/A distance, which in principle allows the intercalation of a single solvent molecule in close contact with both D and A. At the longer distance of 9.54 Å in DMN[10nb]DCV, a smaller contribution of through-solvent interaction can still be detected for polar aromatic solvents but not for acetonitrile. The inherently discontinuous distance dependence of through-solvent interaction and its possible interesting dependence on molecular structure and temperature are discussed.

Investigation of the primary electron transfer processes in some rigidly bridged dyads and triads by (sub)picosecond pump–probe experiments

The electron transfer kinetics of several completely rigid dyads and triads which contain N,N-dimethylaniline (DMA) and dimethoxynaphthalene (DMN) as possible donors and the dicyanovinyl group (DCV) as acceptor were studied by means of (sub)picosecond time-resolved transient absorption spectroscopy. In the dyads DMN[n]DCV, the rate of charge separation decreases exponentially with the number of σ-bonds n in the bridge, the ‘‘damping factor’’ being 0.8 per bond in tetrahydrofuran solvent. In the triads DMA[4]DMN[8]DCV, the primary electron transfer from DMN to DCV occurs in solvents of low and medium polarity within 10 ps in both isomers (syn and anti). The rates of the secondary electron transfer step (formation of the fully charge separated state, DMA+[4]DMN[8]DCV−) and the following deactivation processes depend, however, strongly on the conformation. In acetonitrile, the primary electron transfer involves the two donor groups yielding preferentially DMA+[4]DMN−[8]DCV. In the anti-conformer this state is fairly long-lived; in the syn-conformer, however, it decays rapidly, in part to locally excited triplet states.

Long-lived charge separation in a donor–acceptor dyad adsorbed in mesoporous MCM-41

Irradiation of a rigid donor–{6-bond-bridge}–acceptor dyad [donor = dimethoxynaphthalene (DMN); acceptor = dicyanovinyl (DCV)] occluded within the pores of mesoporous MCM-41 containing aluminium leads to the formation of the DCV radical anion of the dyad with a lifetime of days.

Solvent and Distance Dependent Charge Separation in Rigid Trichromophoric Systems

Transient absorption and time-resolved microwave studies have been carried out on a series of D(onor)2−[bridge]−D(onor)1−[bridge]−A(cceptor) compounds, in which a dimethoxynaphthalene (DMN) primary donor (D1) and a dicyanovinyl (DCV) acceptor are separated by a rigid norbornylogous bridge eight σ-bonds in length and an N,N-dimethylaniline secondary donor (D2) is separated from D1 by a norbornylogous bridge of variable length (four, six, or eight σ-bonds). The identity of the charge-separated state populated upon photoexcitation, i.e., from D1 to A or from D2 to A, depends on the solvent polarity and the length of the bridge separating both donor chromophores. It was found that the final charge-separated state is formed on a (sub)nanosecond time scale, whereas charge recombination shows strong solvent dependence, due to “inverted region” behavior.

Photoinduced giant charge-separated states in a new series of completely rigid covalently linked triads

Preliminary fluorescence and time-resolved microwave conductivity (TRMC) measurements are reported for the novel triad, DMA[4]DMN[8]DCV, in which the three chromophores, DMA (N,N-dimethylaniline), DMN (dimethoxynaphthalene), and DCV (dicyanovinyl), are connected via bridges comprising linearly fused norbornyl and bicyclo[2.2.0]hexyl units, four and eight bonds in length. The triad, DMA[4]DMN[8]DCV, exists in two noninterconvertible syn and anti diastereomeric forms, the former having a U-shaped geometry and the latter having an S-shaped geometry. Samples of the two stereoisomers, labeled H and L, were obtained, but the actual stereochemistry, syn or anti, of each isomer is presently unknown

Photoinduced electron transfer in rigidly linked dimethoxynapthalene-N-methylpyridinium donor-acceptor molecules

Photoinduced electron transfer (ET) is studied in a series of novel molecules containing a dimethoxynaphthalene (DMN) donor and either a pyridine (P) or N-methylpyridinium (P-Me +) acceptor covalently linked via a rigid nonbornalogous bridge ( n sigma bonds in length). ET rates of the order of 10 10 s −1 were measured for the DMN- n-P-Me + series ( n = 4, 6), while no appreciable ET was observed for the DMN- n-P compounds. Electronic and nuclear factors are discussed and the results rationalized in terms of Marcus—Hush and non-adiabatic ET theories.