Acceptor Chromophores Research Articles

Photoinduced Electron Transfer Dynamics of Cyclometalated Ruthenium (II)–Naphthalenediimide Dyad at NiO Photocathode

Both forward and backward electron transfer kinetics at the sensitizer/NiO interface is critical for p-type dye-sensitized photocathodic device. In this article, we report the photoinduced electron transfer kinetics of a Ru(II) chromophore–acceptor dyad sensitized NiO photocathode. The dyad (O26) is based on a cyclometalated Ru(N∧C∧N)(N∧N∧N) (Ru[II]) chromophore and a naphthalenediimide (NDI) acceptor, where N∧C∧N represents 2,2′-(4,6-dimethyl-phenylene)-bispyridine and N∧N∧N represents 2,2′,6′,6″-terpyridine ligand. When the dyad is dissolved in a CH3CN solution, electron transfer to form the Ru(III)–NDI– occurs with a rate constant kf = 1.1 × 1010 s–1 (τf = 91 ps), and electron–hole pair recombines to regenerate ground state with a rate constant kb = 4.1 × 109 s–1 (τb = 241 ps). When the dyad is adsorbed on a NiO film by covalent attachment through the carboxylic acid group, hole injection takes place first within our instrument response time (∼180 fs) followed by the subsequent electron shift onto the ...

Frequency Modulated Femtosecond Stimulated Raman Spectroscopy of Ultrafast Energy Transfer in a Donor–Acceptor Copolymer

A Raman-pump frequency modulation scheme and an automated signal-processing algorithm are developed for improved collection of time-resolved femtosecond stimulated Raman spectra. Together, these two advancements remove the broad background signals endemic to FSRS measurements and retrieve signals with high sensitivity. We apply this frequency-modulated femtosecond stimulated Raman spectroscopy (FM-FSRS) to the characterization of ultrafast energy transport in a copolymer comprised of polystyrene linked oligo(phenylene-ethynylene) donor and thiophene-benzothiadiazole acceptor chromophores. After photoexcitation of the donor, ultrafast energy transfer is monitored by the decay of donor vibrational modes and simultaneous growth of acceptor modes. The FM-FSRS method shows clear advantages in signal-to-noise levels, mitigation of artifact features, and ease of data processing over the conventional FSRS technique.

Influence of the Delocalization Error and Applicability of Optimal Functional Tuning in Density Functional Calculations of Nonlinear Optical Properties of Organic Donor–Acceptor Chromophores

Nonempirically tuned hybrid density functionals with range-separated exchange are applied to calculations of the first hyperpolarizability (β//) and charge-transfer (CT) excitations of linear "push-pull" donor-acceptor-substituted organic molecules with extended π-conjugated bridges. An unphysical delocalization with increasing chain length in density functional calculations can be reduced significantly by enforcing an asymptotically correct exchange-correlation potential adjusted to give frontier orbital energies representing ionization potentials. The delocalization error for a number of donor-acceptor systems is quantified by calculations with fractional electron numbers and from orbital localizations. Optimally tuned hybrid variants of the PBE functional incorporating range-separated exchange can produce similar magnitudes for β// as Møller-Plesset second-order perturbation (MP2) correlated calculations. Improvements are also found for CT excitation energies, with results similar to an approximate coupled-cluster model (CC2).

Dynamics and efficiency of photoinduced charge transport in DNA: Toward the elusive molecular wire

Experimental investigations of photoinduced charge transport in synthetic DNA capped hairpins possessing electron acceptor and donor stilbene chromophores at either end have established the mechanism, dynamics, and efficiency of charge transport in DNA. The mechanism for charge transport in repeating A-T base pairs (A-tracts) was found to change from single-step superexchange at short distances to multistep incoherent hole hopping at longer distances. The rate constants for base-to-base hole hopping in longer A- and G-tract sequences are 1.2 × 109 s–1 and 4.3 × 109 s–1, respectively, considerably slower than the rate constants associated with molecular wires. Even slower rate constants are observed for alternating or random base sequences such as those encountered in natural DNA. The efficiency of charge separation in capped hairpins with A-tract sequences is also low as a consequence of the competition of hole hopping with charge recombination. Significantly higher efficiencies for charge separation are possible using diblock purine base sequences consisting of two or three adenines followed by a larger number of guanines. The short A-block serves as a molecular rectifier, slowing down charge recombination. More efficient charge separation can also be achieved using non-natural bases or by using the triplet acceptor anthraquinone for hole injection.

Excited state intramolecular charge transfer process in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid ethyl ester and effect of acceptor functional groups

Abstract Excited state intramolecular charge transfer (ICT) process in a donor–chromophore–acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid ethyl ester (DMAPPDE) has been investigated spectroscopically in combination with quantum chemical calculations. The molecule DMAPPDE shows dual fluorescence corresponding to emission from the locally excited as well as charge transfer states in polar solvents. Large solvatochromic shift of emission band (Δν = 8504 cm−1), high excited state dipole moment (18 D), quantum chemically calculated potential energy curves by Density Functional Theory (DFT) method and HOMO–LUMO pictures support the occurrence of excited state ICT process. Variation of acceptor strength in this molecular system shows prominent effect on the spectroscopic and molecular properties like absorption and emission band maxima, Stokes’ shift, quantum yields, and dipole moment which are found to be controlled by the ICT process.

ChemInform Abstract: Supramolecular Chemistry of Donor—Acceptor Interactions

AbstractReview: 35 refs.

Synthesis of Dibenzothiophene, Dibenzofuran and Carbazole Donor-Acceptor Chromophores

We present efficient synthetic protocols for functionalizing dibenzothiophene, dibenzofuran, and carbazole with hydroxy and nitro or cyano groups. The synthesis of these donor–acceptor chromophores is based on a key Suzuki–Miyaura coupling using an appropriately substituted aromatic boronic acid. Subsequent intramolecular SNAr reaction allows formation of the dibenzothiophene and dibenzofuran scaffolds, while a carbon–hydrogen activation reaction is employed to afford the carbazole. A final demethylation step unmasks the phenol moiety of the tricyclic chromophores. The UV/Vis absorption properties of the phenol and phenolate forms of these chromophores are also studied.

Photoinduced Electron Transfer as a Probe for the Folding Behavior of Dimethylsilylene-Spaced Alternating Donor–Acceptor Oligomers and Polymers

A series of oligomers and polymers having dimethylsilylene-spaced alternating 4-aminostyrene donor and stilbene acceptor chromophores (two to one) are regioselectively synthesized, and the two donor chromophores are separated by different bridges between two donors. Photophysical tools have been used to examine the folding behavior of these copolymers. Both steady-state and time-resolved fluorescence spectroscopic measurements were examined. The relative intensities (ICT/ILE) between emission from charge-separated state (CT emission) and local excited emission of acceptor chromophore (LE emission) increase with increasing number of repeating units, and reach a plateau, when the linkers between the two aminostyrene chromophores are trimethylene bridges. Replacements of these by dimethylene or tetramethylene linker reduce the relative intensities of CT emission of the polymers, owing to the different folding behavior of these polymers. The CT emission intensity of the polymer with rigid piperazine linkers is much lower than that with trimethylene-bridged copolymer of the same degree of polymerization. Slight conformational change of these polymers would lead to slight variation of the distance between donor and acceptor chromophores so that the nonadiabatic interactions in the excited state between donor–acceptor pairs in these oligomers and polymers would be perturbed by such change of conformations.

Cyanomethylbenzoic Acid: An Acceptor for Donor–π–Acceptor Chromophores Used in Dye‐Sensitized Solar Cells

Sensing the sun: Incorporation of a cyanomethyl benzoic acid electron acceptor into donor-π-acceptor sensitizers for dye-sensitized-solar cell is shown to lead to devices with improved conversion efficiency when compared with more widely used cyanoacetic acid acceptor.

Synthesis, photophysical and photovoltaic properties of a new class of two-dimensional conjugated polymers containing donor–acceptor chromophores as pendant groups

A new design for constructing two-dimensional conjugated copolymers with the D1–A(D2) repeating pattern (A: acceptor, D1: donor 1, D2: donor 2; molecules enclosed in parentheses are pendant groups.), is proposed. D1 and A are employed to construct the linear main-conjugated polymer chain and D2 is situated at the conjugated side chains connected to A. We designed and synthesized a series of D1–A(D2)-type copolymers, in which D1 = diindeno[1,2-b:2′,1′-d]-thiophene (DIDT) or fluorene (F), A(D2) = bis-[4-(dioctylamino)-phenyl] quinoxaline (DOAQX) or bis-[4-(dioctylamino)-phenyl] thieno[3,4-b]pyrazine (DOATP), and D2 = N,N-dioctylanilines. The resultant copolymers, PDIDTDOAQX, PFDOAQX, PDIDTDOATP and PFDOATP, possess at least two strong ICT absorptions, thus resulting in better light harvesting. Their optical and electronic properties were thoroughly investigated experimentally and computationally. Bulk heterojunction photovoltaic cells on the basis of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al configuration were fabricated and characterized. The photovoltaic performances of the devices incorporating these polymers follow the sequence: PDIDTDOAQX > PFDOAQX > PDIDTDOATP > PFDOATP, which is in good agreement with the magnitude of their hole-mobilities.

Interrogating the photogenerated Ir(iv) state of a water oxidation catalyst using ultrafast optical and X-ray absorption spectroscopy

Using sunlight to drive molecular water oxidation catalysts for fuel formation requires understanding the single electron transfer events involved in catalyst activation. In an effort to photogenerate and characterize the highly reactive Ir(IV) state of the Ir(III)-based water oxidation catalyst Cp*Ir(ppy)Cl (ppy = 2-phenylpyridine), we have incorporated the complex into a covalent electron acceptor–chromophore–Cp*Ir(ppy)Cl triad, in which naphthalene-1,8:4,5-bis(dicarboximide) (NDI) is the electron acceptor and perylene-3,4-dicarboximide (PMI) is the chromophore. Photoexcitation of the PMI chromophore in dichloromethane results in two competitive reactions: NDI–1*PMI–Ir(III) → NDI–PMI˙−–Ir(IV) and NDI–1*PMI–Ir(III) → NDI˙−–PMI˙+–Ir(III) that each proceed with τ < 5 ps, as determined by femtosecond transient absorption spectroscopy. Both intermediate ion pairs undergo charge shift reactions to produce NDI˙−–PMI–Ir(IV). The fully charge-separated ion pair has a lifetime of 17.2 ± 0.1 ns, and its photophysical behavior is similar in the more polar solvent benzonitrile. Time-resolved X-ray absorption measurements on the triad at 100 ps following PMI photoexcitation show a new absorption feature at the LIII-edge of Ir and a blue-shifted white-line peak, which provides direct evidence of a change in the Ir oxidation state from Ir(III) to Ir(IV), consistent with the photophysical measurements. Our work underscores the utility of ultrafast spectroscopy performed on covalent assemblies of electron donor–acceptor systems with solar fuels catalysts to generate and probe their higher valence states in ways that complement chemical or electrochemical oxidation and establish the nature of key intermediates implicated in their catalytic mechanisms.

Light-induced charge separation in a donor–chromophore–acceptor nanocomposite poly[TPA-Ru(tpy)2]@ZnO

The synthesis and characterisation of a new donor–chromophore–acceptor system based on poly(vinyltriphenylamine) as the electron donor and a glycine-functionalised bis(2,2′;6′,2′′-terpyridine)ruthenium(II) complex acting both as a chromophore and as an anchor group attached to ZnO nanorods as the electron acceptor are described. The TPA-containing block copolymer was synthesised by Reversible Addition Fragmentation Chain Transfer (RAFT) polymerisation and the ruthenium complex glycine conjugates prepared by Solid Phase Peptide Synthesis (SPPS) were attached via post-polymerisation esterification. GPC, NMR, IR and UV-Visible spectroscopy were used to characterise the multifunctional chromophore–donor polymer. Zinc oxide nanorods were functionalised with the block copolymer by multisite adsorption via the glycine COOH groups. The functionalised nanoparticles were well dispersible in organic solvents. Photoluminescence studies showed a complete quenching of the phosphorescence of the ruthenium chromophore (3MLCT state). Kelvin probe force microscopy (KPFM) was used to confirm that under continuous excitation of the RuII complex (1MLCT) the polymer corona develops a positive charge and thus efficient charge separation between ZnO and the polymer is achieved.

Evaluation of Acceptor Strength in Thiophene Coupled Donor–Acceptor Chromophores for Optimal Design of Organic Photovoltaic Materials

A series of thiophene coupled acceptors were systematically investigated at the density functional theory level to reveal structure-property relationships for building blocks of materials used in organic photovoltaic applications. All of the acceptor groups studied in this work retain their aromaticity when coupled to thiophene groups as estimated from their aromatic stabilization energies. However, pure chains of acceptors may adopt quinoidal geometry along the conjugated backbone depending on the structure of interest. Spearman rank order correlation has been used to assess the relationships between the computed variables such as highest occupied molecular orbital, lowest unoccupied molecular orbital, E(g), oscillator strength, exciton binding energy, aromatic stabilization energy, etc. The relative acceptor strengths were plotted and electrostatic potential maps were generated to examine the charge distribution over the chromophores. It has been found that there is no correlation between acceptor strength and electron withdrawing ability of the acceptor. Electron rich and highly electronegative atoms within acceptor groups mainly affect the charge distribution over the acceptor geometry. Exciton binding energy increases with the increasing aromatic character of the acceptor group. The acceptor strength is inversely correlated with the oscillator strength for the lowest excited state transition.

Efficient Förster Resonance Energy Transfer in 1,2,3-Triazole Linked BODIPY-Zn(II) Meso-tetraphenylporphyrin Donor–Acceptor Arrays

Cu(I) catalyzed azide-alkyne cycloaddition (CuAAC) reactivity was successfully employed to synthesize three donor-acceptor energy transfer (EnT) arrays that contain one (Dyad), three (Tetrad) and four (Pentad) 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) donors connected to a Zn-tetraphenylporphyrin acceptor via 1,2,3-triazole linkages. The photophysical properties of the three arrays, along with individual donor and acceptor chromophores, were investigated by UV-vis absorption and emission spectroscopy, fluorescence lifetimes, and density functional theory (DFT) electronic structure modeling. Comparison of the UV-vis absorption spectra and frontier molecular orbitals from DFT calculations of the three arrays with ZnTPP, ZnTTrzlP, and Trzl-BODIPY shows that the electronic structure of the chromophores is essentially unperturbed by the 1,2,3-triazole linkage. Time-dependent DFT (TDDFT) calculations on the Dyad reproduce the absorption spectra in THF and show no evidence of excited state mixing of the donor and acceptor. The BODIPY singlet excited state emission is significantly quenched in all three arrays, consistent with EnT to the porphyrin core, with efficiencies of 95.8, 97.5, and 97.2% for the Dyad, Tetrad, and Pentad, respectively. Fluorescence excitation spectra of the three arrays, measured at the porphyrin emission, mirror the absorption profile of both the porphyrin and BODIPY chromophores and are consistent with the Förster resonance energy transfer (FRET) mechanism. Applying Förster theory to the spectroscopic data of the chromophores gives EnT efficiency estimates that are in close agreement with experimental values, suggesting that the through-space mechanism plays a dominant role in the three arrays.

Correction to “Photoinduced Multistep Charge Separation in a Heteroleptic Cu(I) Bis(phenanthroline)-Based Donor–Chromophore–Acceptor Triad

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to “Photoinduced Multistep Charge Separation in a Heteroleptic Cu(I) Bis(phenanthroline)-Based Donor–Chromophore–Acceptor TriadMegan S. Lazorski, Riley H. Gest, and C. Michael Elliott*Cite this: J. Am. Chem. Soc. 2012, 134, 50, 20566Publication Date (Web):December 5, 2012Publication History Published online5 December 2012Published inissue 19 December 2012https://doi.org/10.1021/ja3107719Copyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views955Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (116 KB) Get e-Alerts Get e-Alerts

Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution

A new family of π-extended tetrathiafulvalene (exTTF) donor-acceptor chromophores has been synthesized by [2 + 2] cycloaddition of TCNE with exTTF-substituted alkynes and subsequent cycloreversion. X-ray data and theoretical calculations, performed at the B3LYP/6-31G** level, show that the new chromophores exhibit highly distorted nonplanar molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) units. The electronic and optical properties, investigated by UV/vis spectroscopy and electrochemical measurements, are significantly modified when the TCBD acceptor unit is substituted with a donor phenyl group, which increases the twisting of the TCBD units and reduces the conjugation between the two dicyanovinyl subunits. The introduction of phenyl substituents hampers the oxidation and reduction processes and, at the same time, largely increases the optical band gap. An effective electronic communication between the donor and acceptor units, although limited by the distorted molecular geometry, is evidenced both in the ground and in the excited electronic states. The electronic absorption spectra are characterized by low- to medium-intense charge-transfer bands that extend to the near-infrared.

Energy-level modulation of organic alkynes by click chemistry

A series of novel donor–acceptor chromophores have been successfully synthesized in excellent yield by metal-free [2+2] click chemistry, which was effective in the energy-level modulation. Structures of the conjugated compounds were fully characterized by NMR, IR, and MS. By introducing TCNE, TCNQ, F4-TCNQ click monomers, we obtained energy-level tunable materials in high solubility, which was beneficial for processing. It has been demonstrated that the absorption characteristics of all the newly prepared compounds have been strongly bathochromically shifted with an end-absorption far into the near infrared region due to the efficient intramolecular charge-transfer (CT) interaction. The electrochemical properties have been studied by cyclic voltammograms indicating good agreement between the electrochemical and optical band gaps determined by the end absorption.

Construction of Donor–Acceptor Chromophores in Platinum Polyyne Polymer by [2 + 2] Cycloaddition of Organic Acceptors

AbstractA thiophene‐containing platinum polyyne polymer was postfunctionalized by a [2 + 2] cycloaddition followed by a cycloreversion of tetracyanoethylene (TCNE) or 7,7,8,8‐tetracyanoquinodimethane (TCNQ), yielding narrow band gap polymers. The quantitative addition of the acceptor molecules was confirmed by combined analytical techniques. The postfunctionalized platinum polyyne polymers displayed charge‐transfer (CT) bands in the visible‐near IR region and potent redox activities. The TCNQ adduct has a stronger electron‐accepting feature than the TCNE adduct, as revealed by the more bathochromically shifted CT band and the lower first reduction potential. The systematic investigation revealed a clear correlation between the optical and electrochemical band gaps.

Inside Cover: Hydrogen-Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States (Chem. Eur. J. 32/2012)

Inside Cover: Hydrogen-Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States (Chem. Eur. J. 32/2012)

Hydrogen‐Bonding Induced Alternate Stacking of Donor (D) and Acceptor (A) Chromophores and their Supramolecular Switching to Segregated States

This paper reports comprehensive studies on the mixed assembly of bis-(trialkoxybenzamide)-functionalized dialkoxynaphthalene (DAN) donors and naphthalene-diimide (NDI) acceptors due the cooperative effects of hydrogen bonding, charge-transfer (CT) interactions, and solvophobic effects. A series of DAN as well as NDI building blocks have been examined (wherein the relative distance between the two amide groups in a particular chromophore is the variable structural parameter) to understand the structure-dependent variation in mode of supramolecular assembly and morphology (organogel, reverse vesicle, etc.) of the self-assembled material. Interestingly, it was observed that when the amide functionalities are introduced to enhance the self-assembly propensity, the mode of co-assembly among the DAN and NDI chromophores no longer remained trivial and was dictated by a relatively stronger hydrogen-bonding interaction instead of a weak CT interaction. Consequently, in a highly non-polar solvent like methylcyclohexane (MCH), although kinetically controlled CT-gelation was initially noticed, within a few hours the system sacrificed the CT-interaction and switched over to the more stable self-sorted gel to maximize the gain in enthalpy from the hydrogen-bonding interaction. In contrast, in a relatively less non-polar solvent such as tetrachloroethylene (TCE), in which the strength of hydrogen bonding is inherently weak, the contribution of the CT interaction also had to be accounted for along with hydrogen bonding leading to a stable CT-state in the gel or solution phase. The stability and morphology of the CT complex and rate of supramolecular switching (from CT to segregated state) were found to be greatly influenced by subtle structural variation of the building blocks, solvent polarity, and the DAN/NDI ratio. For example, in a given D-A pair, by introducing just one methylene unit in the spacer segment of either of the building blocks a complete change in the mode of co-assembly (CT state or segregated state) and the morphology (1D fiber to 2D reverse vesicle) was observed. The role of solvent polarity, structural variation, and D/A ratio on the nature of co-assembly, morphology, and the unprecedented supramolecular-switching phenomenon have been studied by detail spectroscopic and microscopic experiments in a gel as well as in the solution state and are well supported by DFT calculations.