Acceptor Chromophores Research Articles

Strong Charge‐Transfer Chromophores from [2+2] Cycloadditions of TCNE and TCNQ to Peripheral Donor‐Substituted Alkynes

AbstractPeripheral donor‐substituted N,N‐dimethyl‐4‐[(7‐nitrobenzo[c][1,2,5]thiadiazol‐4‐yl)ethynyl]aniline (1a), 4‐(benzo[c][1,2,5]thiadiazol‐4‐ylethynyl)‐N,N‐dimethylaniline (1b), and 4,4′‐{benzo[c][1,2,5]thiadiazole‐4,7‐diylbis(ethyne‐2,1‐diyl)}bis(N,N‐dimethylaniline) (2) were prepared by Sonogashira cross‐coupling reactions. Compounds 1a, 1b, and 2 subsequently reacted with tetracyanoethylene (TCNE) or 7,7,8,8‐tetracyanoquinodimethane (TCNQ) to afford the charge‐transfer chromophores 3–8. X‐ray crystallographic analysis revealed the nonplanarity of these donor–acceptor (D–A) chromophores. Cyclic voltammetry (CV) exhibited a multistep reduction wave. UV/Vis spectra and theoretical calculations identified efficient intramolecular charge‐transfer interactions. Moreover, scanning electron microscopy (SEM) showed the morphology transition and reconstruction process of 5 from 0D hollow nanospheres to 1D tubular microstructures.

Origin of Second-Order Nonlinear Optical Effects of Nonpoled Donor–Acceptor Chromophores on Surface

Thin films of alkyl conjugated donor–acceptor (D–A) molecules, prepared by a high-yielding addition reaction between electron-rich alkynes and tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ), were investigated by ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopy, in-plane and out-of-plane X-ray diffraction (XRD), and second-harmonic generation (SHG) measurements. The variable self-assembling ability of D–A chromophores produced different molecular orientations in the thin films. The TCNQ-adducted D–A molecule formed a centrosymmetric bilayer structure based on the strong interactions between the chromophores, while the film of the TCNE-adducted counter molecule was composed of interdigitated alkyl layers and randomly oriented chromophores due to their weak interactions. The interfacial interactions between a substrate and a TCNE-adducted molecular layer were expected to induce a noncentrosymmetric chromophore orientation in the thin film, which produced an effective SHG coefficient (deff) of ca. 21 pm V-1 without electric poling.

Origin of Second-Order Nonlinear Optical Effects of Nonpoled Donor–Acceptor Chromophores on Surface

Origin of Second-Order Nonlinear Optical Effects of Nonpoled Donor–Acceptor Chromophores on Surface

Spectroscopic investigation of novel donor–acceptor chromophores as specific application agents for opto-electronics and photonics

Donor–acceptor chromophores were synthesized by Knoevenagel condensation and characterized by using spectroscopic measurements (FT-IR, 1H NMR, 13C NMR, and mass) and elemental analyses. UV–Vis and fluorescence spectroscopic studies provided that these dyes are good absorbent and fluorescent. The results of photostability study showed that photobleaching of Dyes 2 and 4 was more significant than that of Dyes 1 and 3, providing that Dyes 1 and 3 are more photostable than Dyes 2 and 4. In addition, all dyes included in this study are found to be sensitive to the polarity of the microenvironment provided by different solvents based on the results of fluorescence polarity studies.

ChemInform Abstract: Adapting Semiconducting Polymer Doping Techniques to Create New Types of Click Postfunctionalization

AbstractReview: 77 refs.

Comparison of CC Triple and Double Bonds as Spacers in Push–Pull Chromophores

AbstractWe report the synthesis and properties of two series of homologous donor–acceptor (D–A) chromophores in which N,N‐dimethylanilino (DMA) or N,N‐dihexylanilino (DHA) donors and dicyanovinyl acceptors are separated by up to four C≡C triple‐bond spacers or up to three C=C double‐bond spacers. The intramolecular charge‐transfer (CT) interactions of the new D–A oligoynes and the known all‐trans D–A oligoenes were investigated by X‐ray crystallography, electrochemistry, UV/Vis spectroscopy, and theoretical calculations. In both series, the optical and electrochemical HOMO–LUMO gaps decrease with increasing spacer length. The HOMO–LUMO gaps for the D–A oligoynes and oligoenes with a given spacer length are nearly identical. The effect of the spacer length was found to level‐off for spacers with more than six carbon atoms. The third‐order optical nonlinearity of both series of molecules was determined by measuring the rotational averages of the third‐order polarizabilities γrot by degenerate four‐wave mixing.

A convenient synthesis of new chromophoric tetracyanobutadiene-scaffolded peptides via a dipolar [2+2] cycloaddition–cycloreversion reaction

Herein, we report a novel approach for the synthesis of π-conjugated peptide-based donor–acceptor (D-π-A) chromophores, by reacting electron-rich alkynes with tetracyanoethylene. The desired tetracyanobutadiene-scaffolded peptides were obtained in good yields with various optical properties, λ max: 321–492 nm, ε: 21,000–65,000 mol −1 dm 3 cm −1 depending on the substitution pattern of the cyanobutadiene scaffold.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

The excited state intramolecular charge transfer process in donor–chromophore–acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO–LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Inside Cover: Hydrogen‐Bonding Directed Assembly and Gelation of Donor–Acceptor Chromophores: Supramolecular Reorganization from a Charge‐Transfer State to a Self‐Sorted State (Chem. Eur. J. 22/2011)

In a mixed assembly of bis-amide-functionalized dialkoxynaphthalene donor and naphthalenediimide acceptor, when there was a mismatch in the relative distance of the amide groups with respect to the two chromophores, self-sorting was observed. On the other hand if the two distances almost matched, a stable charge-transfer gel was formed in tetrachloroethylene. For more details see the Communication by S. Ghosh et al. on page 6061 ff.

Hydrogen‐Bonding Directed Assembly and Gelation of Donor–Acceptor Chromophores: Supramolecular Reorganization from a Charge‐Transfer State to a Self‐Sorted State

Hydrogen‐Bonding Directed Assembly and Gelation of Donor–Acceptor Chromophores: Supramolecular Reorganization from a Charge‐Transfer State to a Self‐Sorted State

Ultrafast Photosensitization of Phthalocyanines through Their Axial Ligands

We have studied the energy transfer properties of a novel silicon phthalocyanine that coordinates two anthracene-9-carboxylate groups in the form of trans axial ligands. Our objectives were to generate a system with auxiliary chromophores that enhance the light absorption properties of the macrocycle in a specific region in the UV and to evaluate the efficiency and time scales for energy transfer. The ligand coordination through a carboxylate group directly attached to the anthracenic system allows for close proximity of the donor and acceptor chromophores. The energy transfer process was observed to be nearly 100% efficient and to occur on a time scale of 370 fs. From the energy relations of the donor and acceptor states and the observed dynamics, the initial energy transfer step is likely to involve upper electronic states of the phthalocyanine rather than the states of the lowest-energy vibroelectronic Q bands.

Microwave‐assisted TCNE/TCNQ addition to poly(thienyleneethynylene) derivative for construction of donor–acceptor chromophores

AbstractThe alkyne moieties of poly(3‐hexylthienyleneethynylene) were reacted with tetracyanoethylene or 7,7,8,8‐tetracyanoquinodimethane by microwave irradiation to produce donor–acceptor chromophores in the polymer main chain. The resulting polymers were fully characterized by GPC, 1H NMR, and IR spectroscopies, and elemental analyses. They were both thermally and chemically stable, as revealed by thermogravimetric analyses and ESR measurements. UV–vis‐NIR spectroscopy revealed charge‐transfer bands in the low‐energy region, and electrochemistry confirmed the narrower band gaps with the elevated HOMO and lower LUMO levels relative to the precursor polymer. To take advantage of these postfunctionalization methods, p‐type doping of the polymers with I2 was attempted. Room temperature conductivities of the postfunctionalized polymers reached 4.5 × 10−5 S cm−1, which was about 10 times greater than that of the precursor polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

A generalized supramolecular strategy for self-sorted assembly between donor and acceptor gelators

An effective supramolecular strategy for self-sorting between naphthalene-diimide (NDI) acceptor and dialkoxy-naphthalene (DAN) donor organogelators is reported. The concept is based on mismatch in the placement of the two amide functionalities in the donor and acceptor chromophores so that self-sorting ensured maximum effect of H-bonding.

Switchable Three-State Fluorescence of a Nonconjugated Donor−Acceptor Triarylborane

A nonconjugated fluorescent molecule with a triarylboron acceptor and an alkylamine donor has been found to display bright green fluorescence due to charge transfer through space, which can be reversibly deactivated by blocking either the donor or acceptor site. Binding of the fluoride ion to boron switches the fluorescence color to sky blue, while protonation of the amine with acid switches the emission color to the purple fluorescence of the acceptor chromophore.

Energy level tuning of polythiophene derivative by click chemistry‐type postfunctionalization of side‐chain alkynes

AbstractA polythiophene derivative substituted with electron‐rich alkynes as a side chain was synthesized using the Suzuki polycondensation reaction. The electron‐rich alkynes underwent the “click chemistry”‐type quantitative addition reaction with strong acceptor molecules, such as tetracyanoethylene (TCNE) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ), resulting in the formation of donor–acceptor chromophores. All polymers showed excellent solubilities in the common organic solvents as well as good thermal stabilities with their 5% decomposition temperatures exceeding 230 °C. The TCNE‐/TCNQ‐adducted polymers displayed well‐defined charge‐transfer (CT) bands in the low energy region. The CT energy of the TCNE‐adducted polymer was 2.56 eV (484 nm), which was much greater than that of the TCNQ‐adducted polymer [1.65 eV (750 nm)]. This result was supported by the electrochemical measurements. The electrochemical band gaps of the TCNE‐adducted polymers were much greater than those of the corresponding TCNQ‐adducted polymers. Furthermore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, determined from the first oxidation and first reduction peak potentials, respectively, decreased with the increasing acceptor addition amount. All these results suggested that the energy levels of the polythiophene derivative can be tuned by varying the species and amount of the acceptor molecules using this postfunctionalization method. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

Near infrared organic light-emitting diodes based on acceptor–donor–acceptor (ADA) using novel conjugated isatin Schiff bases

Abstract Fabrications of a single layer organic light emitting diodes (OLEDs) based on two conjugated acceptor–donor–acceptor (ADA) isatin Schiff bases are described. The electroluminescent spectra of these materials range from 630 to 700 nm and their band gaps were measured between 1.97 and 1.77 eV. The measured maximum external quantum efficiencies (EQE) for fabricated OLEDs are 0.0515% and 0.054% for two acceptor–donor–acceptor chromophores. The Commission International De L’Eclairage (CIE) (1931) coordinates of these two compounds were attained and found to be (0.4077, 0.4128) and (0.4411, 0.4126) for two used acceptor–donor–acceptor chromophores. The measured I – V curves demonstrated the apparent diode behavior of two ADA chromophores. The turn-on voltages in these OLEDs are directly dependent on the thickness. These results have demonstrated that ADA isatin Schiff bases could be considered as promising electroluminescence-emitting materials for fabrication of OLEDs.

Optimal Efficiency of Self-Assembling Light-Harvesting Arrays

Using a classical master equation that describes energy transfer over a given lattice, we explore how energy transfer efficiency along with the photon capturing ability depends on network connectivity, on transfer rates, and on volume fractions-the numbers and relative ratio of fluorescence chromophore components, e.g., donor (D), acceptor (A), and bridge (B) chromophores. For a one-dimensional AD array, the exact analytical expression (derived in Appendix A) for efficiency shows a steep increase with a D-to-A transfer rate when a spontaneous decay is sufficiently slow. This result implies that the introduction of B chromophores can be a useful method for improving efficiency for a two-component AD system with inefficient D-to-A transfer and slow spontaneous decay. Analysis of this one-dimensional system can be extended to higher-dimensional systems with chromophores arranged in structures such as a helical or stacked-disk rod, which models the self-assembling monomers of the tobacco mosaic virus coat protein. For the stacked-disk rod, we observe the following: (1) With spacings between sites fixed, a staggered conformation is more efficient than an eclipsed conformation. (2) For a given ratio of A and D chromophores, the uniform distribution of acceptors that minimizes the mean first passage time to acceptors is a key point to designing the optimal network for a donor-acceptor system with a relatively small D-to-A transfer rate. (3) For a three-component ABD system with a large B-to-A transfer rate, a key design strategy is to increase the number of the pathways in accordance with the directional energy flow from D to B to A chromophores. These conclusions are consistent with the experimental findings reported by Francis, Fleming, and their co-workers and suggest that synthetic architectures of self-assembling supermolecules and the distributions of AD or ABD chromophore components can be optimized for efficient light-harvesting energy transfer.

Synthesis and photophysical properties of five-membered ring π-conjugated materials based on bisthiazol-2-yl-amine and their metal complexation studies

Poly(5,5′-(2-hexyldecyl)-bisthiazol-2-yl-amine) ( PBTA) is prepared by nickel(0) mediated Yamamoto-type coupling. The photoluminescence (PL) spectrum of PBTA in THF solution displays pure blue emission with a peak centered at 444 nm without any shoulder peaks and the HOMO and LUMO values for PBTA are estimated to be 5.11 and 2.90 eV, respectively. In addition, we have synthesized a novel bisthiazol-2-yl-amine ( BTA)-cored donor–acceptor (D–A) chromophore system, namely 5-(4-(diphenylamino)phenyl)- N-(5-(4-(diphenylamino)phenyl)thiazol-2-yl)- N-octylthiazol-2-amine ( 2- TPA- BTA) in which the electron-donating (D) moiety is triphenylamine group and the electron-withdrawing (A) unit is thiazole group. Furthermore, in this report, we present the complexation studies of both the BTA and 2- TPA- BTA chromophores with Cu(II) and Pd(II), respectively. The crystal structures are established by single-crystal X-ray diffraction analysis. These studies not only provide the general photophysical principles of the materials based on BTA moiety but also encourage progress toward realizing the full potential of its hybrid metal–organic frameworks.

Self‐Sorted Assembly in a Mixture of Donor and Acceptor Chromophores

A simple and novel supramolecular approach for orthogonal self-assembly of donor and acceptor chromophores has been demonstrated. Suitably designed 1,5-dialkoxynaphthalene (DAN) and naphthalene tetracarboxylic acid diimide (NDI) derivatives were used as the donor and acceptor systems, respectively. The molecular design for self-sorting relies upon the precise control over the placement of the self-complementary hydrogen-bonding units (amide functionality) with respect to the individual chromophore. By design, the distances between the two amide groups in the donor and acceptor chromophores are not identical, and consequently the effect of the hydrogen-bonding interaction cannot be maximised in the case of alternate donor-acceptor-type pi-stacking. Thus a relatively weak charge-transfer interaction is expected to be sacrificed, and segregated assembly among the individual chromophores should be enforced by virtue of the much stronger effects of hydrogen bonding and pi-pi stacking. Detailed spectroscopic studies were carried out to probe the mode of self-assembly in various derivatives of the DAN-NDI donor-acceptor pairs to establish the utility of the molecular design as a generalised one for orthogonal self-assembly.

Double‐Bond versus Triple‐Bond Bridges: Does it Matter for the Charge‐Transfer Absorption by Donor–Acceptor Chromophores?

Double-Bond versus Triple-Bond Bridges : Does it Matter for the Charge-Transfer Absorption by Donor-Acceptor Chromophores?