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A wide variety of organic dyes form, under certain conditions, clusters know as J- and H-aggregates. Cyanine dyes are such a class of molecules where the spatial proximity of several dyes leads to overlapping electron orbitals and thus to the creation of a new energy landscape compared to that of the individual units. In this work, we create artificial H-aggregates of exactly two Cyanine 3 (Cy3) dyes by covalently linking them to a DNA molecule with controlled subnanometer distances. The absorption spectra of these coupled systems exhibit a blue-shifted peak, whose intensity varies depending on the distance between the dyes and the rigidity of the DNA template. Simulated vibrational resolved spectra, based on molecular orbital theory, excellently reproduce the experimentally observed features. Circular dichroism spectroscopy additionally reveals distinct signals, which indicates a chiral arrangement of the dye molecules. Molecular dynamic simulations of a Cy3-Cy3 construct including a 14-base pair DNA sequence verified chiral stacking of the dye molecules. [ABSTRACT FROM AUTHOR]

Low rylene (R) and rylene diimides (RD) are important organic semiconductors and dyes. High R and RD with larger conjugated cores show different properties compared with their low counterparts. Herein, absorption spectra, frontier molecular orbitals, band gaps, inner-sphere reorganization energy (λi), ionization potential, electron affinity, and atomic charge population of 20 rylene compounds were calculated by the density functional theory method. The theoretical results agree well with experimental ones. We predict some unusual properties of some high rylene derivatives that are unknown compounds due to synthetic difficulties. The lowest unoccupied molecular orbital energy levels of RD compounds change slightly, from −3.61 to −3.79 eV, which makes them strong electron acceptors. The band gaps narrow with the size increase of conjugated cores, which makes high rylene derivatives near-infrared dyes. The rising highest occupied molecular orbital energy levels of high rylene derivatives makes them unstable in the air. The λi falls with the size increase of the conjugated core, and the size of RD-4 or R-4 is big enough for the small λi to favor charge transport. The charge population analysis indicates R and RD have different charge distribution under the effect of electron-withdrawing imide groups, which contributes to distinct properties. [ABSTRACT FROM AUTHOR]

Three new metal-free organic dyes with the [1]benzothieno[3,2-b]benzothiophene (BTBT) p-bridge, having the structure donor-p-acceptor (D-π-A) and labeled as 19, 20 and 21, have been designed and synthesized for application in dye-sensitized solar cells (DSSC). Once the design of the π-acceptor block was fixed, containing the BTBT as the π-bridge and the cyanoacrylic group as the electron acceptor and anchoring unit, we selected three donor units with different electron-donor capacity, in order to assemble new chromophores with high molar extinction coefficients (ε), whose absorption features well reflect the good performance of the final DSSC devices. Starting with the 19 dye, which shows a molar extinction coefficient ε of over 14,000 M-1 cm-1 and takes into account the absorption maximun at the longer wavelength, the substitution of the BFT donor unit with the BFA yields a great enhancement of absorptivity (molar extinction coefficient ε > 42,000 M-1 cm-1), until reaching the higher value (ε > 69,000 M-1 cm-1) with the BFPhz donor unit. The good general photovoltaic performances obtained with the three dyes highlight the suitable properties of electron-transport of the BTBT as the π-bridge in organic chromophore for DSSC, making this very cheap and easy to synthesize molecule particularly attractive for efficient and low-cost photovoltaic devices. [ABSTRACT FROM AUTHOR]

Quantumdots (QDs) offer distinct advantages over organic dyes and fluorescentproteins forbiological imaging applications because of their brightness, photostability,and tunability. However, a major limitation is that single QDs emitfluorescent light in an intermittent on-and-off fashion called “blinking”.Here we report the development of blinking-suppressed, relativelycompact QDs that are able to maintain their favorable optical propertiesin aqueous solution. Specifically, we show that a linearly gradedalloy shell can be grown on a small CdSe core via a precisely controlledlayer-by-layer process, and that this graded shell leads to a dramaticsuppression of QD blinking in both organic solvents and water. A substantialportion (>25%) of the resulting QDs does not blink (more than 99%of the time in the bright or “on” state). Theoreticalmodeling studies indicate that this type of linearly graded shellnot only can minimize charge carrier access to surface traps but alsocan reduce lattice defects, both of which are believed to be responsiblefor carrier trapping and QD blinking. Further, we have evaluated thebiological utility of blinking-suppressed QDs coated with polyethyleneglycol (PEG)-based ligands and multidentate ligands. The results demonstratethat their optical properties are largely independent of surface coatingsand solvating media, and that the blinking-suppressed QDs can providecontinuous trajectories in live-cell receptor tracking studies. [ABSTRACT FROM AUTHOR]

The convenient synthesis of a new class of conjugated aza-BODIPY derivatives from readily available precursors has been achieved. The new materials bear close structural similarity to BODIPYs but differ significantly in electronic configuration from known derivatives, leading to markedly different absorption and emission properties. [ABSTRACT FROM AUTHOR]

New organic dyes containing fluorene functionalized with two imidazole chromophores as donors and cyanoacrylic acid acceptors have been synthesized and successfully demonstrated as sensitizers in nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). The monoimidazole analogues were also synthesized for comparison. The Sommelet reaction of bromomethylated 2-bromo-9,9-diethyl-9H-fluorene produced the key precursor 7-bromo-9,9-diethyl-9H-fluorene-2,4-dicarbaldehyde required for the preparation of imidazole-functionalized fluorenes. Since the dyes possess weak donor segment, the electron-richness of the conjugation pathway dictated the optical, electrochemical, and photovoltaic properties of the dyes. The dyes served as sensitizers in DSSC and exhibited moderate efficiency up to 3.44%. The additional imidazole present on the fluorene has been found to retard the electron recombination due to the bulkier hydrophobic environment and led to high open-circuit voltage in the devices. [ABSTRACT FROM AUTHOR]

This article describes the new multidimensional spectroscopy technique triply resonant sum frequency spectroscopy, a four-wave mixing technique sharing advantages of both 2D-IR and resonance Raman experiments. In this technique, lasers with three independent frequencies interact coherently within a sample and generate an output frequency at their triple summation. The output intensity depends on coupled electronic and vibrational resonances in the sample. We use an organic dye as a model system to demonstrate fully resonant, fully coherent multidimensional spectroscopy using two independently tunable mid-infrared vibrational interactions and one visible electronic interaction. When the pulses are time ordered, the method has a single coherence pathway, eliminating interference between pathways. Fundamental vibrational transitions appear on one axis and overtones and combinations bands on the other, allowing anharmonicities of the modes to be determined easily and conveying molecular coupling information. The experiments demonstrate coupling between seven vibrational ring modes and an electronic state, the resolution of a Fermi resonance, detection of low concentrations, elimination of excitation pulse scattering and fluorescence, background suppression of solvent and co-solutes, and observation of coherence dephasing dynamics. The electronic resonance enhancements used in this methodology are similar to the enhancements responsible for resonance Raman spectroscopy and can be considered resonance 2D-IR spectroscopy. [ABSTRACT FROM AUTHOR]

Diffusion of organic dyes in neat room temperature ionic liquid (RTIL) and RTIL-mixed micelle has been studied by fluorescence correlation spectroscopy (FCS). We have selected two RTILs, 3-pentyl-1-methyl imidazolium bromide ([C5C1Im][Br]) and the corresponding tetra-fluoroborate ([C5C1Im][BF4]). Diffusion coefficients (Dt) of three organic dyesDCM (neutral), C480 (neutral), and C343 (anionic)in these RTILs are ∼100 times slower compared to water. This indicates very high viscosity of the RTILs. In contrast to water, the Dtin RTIL exhibits a wide distribution which suggests the presence of heterogeneity (nanoscale organization). The presence of ions in the RTILs markedly affects diffusion in the RTILs. Dt's of C480 (neutral) and C343 (anionic) are very similar in water but in RTILs the ionic dye C343 diffuses 1.7 times slower than neutral C480. This is attributed to the electrostatic force exerted by the ions in the RTILs. In the giant (∼2–4 μm) [C5C1Im][Br]-triblock copolymer (P123) mixed micelle Dtof DCM, C480, and C343 are found to be 7, 15, and 7 μm2s–1, respectively. The results are compared with those in P123 micelle and gel. [ABSTRACT FROM AUTHOR]

New organic dyes containing a diarylaminofluorene unit as an electron donor and cyanoacrylic acid as acceptor and anchoring group in a donor-π-donor-π-acceptor architecture have been synthesized and characterized as sensitizers for nanocrystalline TiO2-based dye-sensitized solar cells. They have shown three major electronic absorptions originating from the π-π* and charge-transfer transitions covering the broad visible range (250-550 nm) in solution. The charge-transfer transition of the dyes exhibited negative solvatochromism, suggesting a polarized ground state. They have also displayed acidochromism in solution owing to the presence of a protonation-deprotonation equilibrium. On comparison with the triphenylamine and carbazole-based parent dyes (E)-2-cyano-3-(4-(diphenylamino)phenyl)acrylic acid and (E)-2-cyano-3-(9-ethyl-9H-carbazol-3-yl)acrylic acid they exhibited longer wavelength absorptions and facile oxidation, indicating the stronger electron-donating ability of the auxiliary chromophores. In addition, they exhibited nearly two times larger light-to-electron conversion efficiency under simulated AM 1.5 G irradiation (100 mW cm-2) with an aperture mask when compared to the parent dyes. Among the new dyes, the one containing the naphthylphenylamine segment showed better device characteristics attributable to the higher HOMO energy level which probably facilitates the regeneration of the dye and effective suppression of the back reaction of the injected electrons with the I3- in the electrolyte. The optical properties of the dyes were modeled using TDDFT simulations employing different theoretical models (B3LYP, CAM-B3LYP, and MPW1K), and the best correlations with the observed parameters have been found for CAM-B3LYP and MPW1K calculations. The electron lifetimes extracted from the electrochemical impedance measurements of the dye-sensitized solar cells were used to interpret the solar cell efficiency alternations. [ABSTRACT FROM AUTHOR]

Elucidation of photoinduced charge transfer behavior in organic dye/metal hybrids is important for developing photocatalytic systems for solar energy conversion. We report the synthesis and photophysical characterization of a perylene-3,4:9,10-bis(dicarboximide) (PDI)–ruthenium(II) complex, bis-PDI-2,2′-bipyridineRu(II)Cl2(CNtbutyl)2, which has favorable energetics, ΔGCS≈ −1.0 eV, for singlet electron transfer from the Ru complex to PDI. Time-resolved optical spectroscopy reveals that upon selective photoexcitation of PDI, ultrafast charge transfer (<150 fs) from the Ru complex to 1*PDI generates the Ru(III)–PDI–•ion pair. The resulting vibrationally hot Ru(III)–PDI–•ion pair exhibits fast relaxation (τ = 3.9 ps) and charge recombination (τCR= 63 ps). Our experimental and computational (DFT and TDDFT) studies show that energy-preserving photodriven singlet electron transfer can dominate in properly designed organic dye/metal complexes, making them of particular interest for use in artificial photosynthetic systems for solar fuels formation. [ABSTRACT FROM AUTHOR]

The 1H NMR chemical shifts were theoretically computed for the organic dyes 2-(2,6-dimethyl-4H-pyran-4-ylidene)-malononitrile (1), cyano-(2,6-dimethyl-4H-pyran-4-ylidene)-acetic acid methyl ester (2), 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-malononitrile (3), and methyl 2-(2,6-bis(4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (4) at the GIAO/B3LYP/6-311(d,p)//B3LYP/6-311(d,p) level of theory. Moreover, the intramolecular rotational barriers of the molecules were calculated to evaluate the internal flexibility with respect to the torsional degrees of freedom, and the nuclear-independent chemical shifts (NICS) were employed to analyze the ring currents. The difference was explained in terms of intramolecular hydrogen bonds and ring currents of the molecules. The 1H NMR spectra were reproduced by experiments for the comparison with computationally constructed data. Our results suggest a good guideline in interpreting 1H NMR chemical shifts using computational methods and furthermore a reliable perspective for designing molecular structures. [ABSTRACT FROM AUTHOR]

The quest of organic dyes presenting improved electronic features has been extremely active during the last decades, as new structures are necessary to build novel materials such as dye-sensitized solar cells, nonlinear optics commutators, or molecular photochromic switches. Cyanine derivatives occupy a key spot in that scene, as they present intense absorption bands and tunable colors, even when a relatively short π-conjugated path is used. This behavior has often been interpreted as a consequence of a negligible bond length alternation. Recently, Thorley et al. have designed and characterized new cationic compounds that possess the cyanine electronic features, though presenting sizable bond length alternation (Angew. Chem. Int. Ed.2008, 47, 7095−7098). In this contribution, I investigate, with quantum mechanical tools, the size dependence of these properties in model symmetric dyes displaying Thorley’s patterns. Extended chains are simulated in order to obtain insights into the chain length convergence, and the results are compared to those obtained at the same level of theory for classical cyanine architectures. This theoretical work is a step toward the rational development of more efficient π-conjugated compounds. [ABSTRACT FROM AUTHOR]

Fluorescence correlation spectroscopy (FCS) has been used to study the motion of fluorescent dyes in a giant (diameter 20 000 nm = 20 μm) catanionic vesicle comprised of the surfactant sodium dodecyl sulfate (SDS) and dodecyltrimethyl ammonium bromide (DTAB). The diffusion in the anion (SDS) rich catanionic vesicle was studied both in bulk water and in an immobilized vesicle attached to a positively charged glass surface. In the case of the immobilized vesicle, the diffusion coefficients (Dt) of R6G (rhodamine 6G), DCM (4-dicyanomethylene-2-methyl-6-p-dimethyl aminostyryl-4H-pyran), and C343 (coumarin 343) are found to be 1.5, 2.5, and 10 μm2/s, respectively, which are 280, 120, and 55 times slower compared to those for the same dyes in bulk water. The magnitude of Dtis found to vary for different vesicles. This was attributed to the difference in size and shape of the immobilized vesicles. In bulk, R6G binds completely to the vesicle and exhibits extremely slow diffusion with Dt= 0.5 ± 0.1 μm2/s (∼850 and 3 times slower compared to that of R6G in bulk water and within the immobilized vesicle). This is attributed to very slow overall diffusion of the very large size vesicles (20 μm = 20 000 nm). Both of the dye molecules (DCM and C343) show two different diffusion coefficients for the vesicles in bulk. In this case, the small Dt(0.5 ± 0.1 μm2/s) corresponds to the diffusion of the vesicle as a whole and the large Dtvalue (300 and 550 μm2/s for DCM and C343, respectively) corresponds to the free dye molecules in bulk water. [ABSTRACT FROM AUTHOR]

The synthesis, electronic properties, and performance in dye-sensitized solar cells (DSSC5) of four cone-shaped organic dyes (ITD, UFD-Th, ITD-Hx, and ITD-OM) containing the isotruxene π-scaffold are reported. Selective substitution of the unsymmetrical isotruxene core with two diarylamino donors and one cyanocarboxylic acid acceptor was achieved by using a prefunctionalized dibromoisotruxene building block. The ortho-para-branched isotruxene core allows strong electronic couplings among the donors and the acceptor, leading to red-shifted absorption profiles with significant charge-transfer character. All four isotruxene dyes display reversible anodic waves in cyclic voltammagrams with both 1-LOMO and LUMO potentials suitable for application in DSSCs. The DSSCs fabricated with these cone- shaped organic dyes exhibited high open-circuit voltages (0.67-0.76 V) and fill factors (0.67-0.72) with a power conversion efficiency (η) up to 5.45%, which is 80% of the ruthenium dye N7 19-based standard cell fabricated and measured under the same conditions. [ABSTRACT FROM AUTHOR]

We employ the 4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT) segment as a conjugated spacer to construct an extremely high-molar-absorption-coefficient organic chromophore for dye-sensitized solar cells, exhibiting a high power conversion efficiency of 8.95% measured under irradiation of 100 mW cm−2 AM1.5G sunlight. Our comparative experiments have proved the prominent merit of employing CPDT instead of the prevailing 2,2′-dithiophene (DT) as the building block for the further dye design. We also have demonstrated that a controllable coassembling of dye molecules and electrolyte components on semiconducting nanocrystals can reduce surface states and inhibit charge recombination synchronously. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) optical coherent spectroscopy that correlates the double excited electronic states to constituent single excited states is described. The technique, termed two-dimensional double-quantum coherence spectroscopy (2D-DQCS), makes use of multiple, time-ordered ultrashort coherent optical pulses to create double and single quantum coherences over the time intervals between the pulses. The resulting 2D electronic spectra map out the energy correlation between the first excited state and two-photon-allowed double-quantum states. Measurements of organic dye molecules show that the near-resonant energy offset for adding a second electronic excitation to the system relative to the first excitation is on the order of tens of millielectronvolts. Simulations of DQC spectra show that vibronic transitions add rich features to the 2D spectra. The results of quantum chemical calculations on model systems provide insight into the many-body origin of the energy shift measured in the experiment. These results demonstrate the potential of 2D-DQCS for elucidating quantitative information about electron−electron interactions, many-electron wave functions, and electron correlation in electronic excited states and excitons. [ABSTRACT FROM AUTHOR]

Two indole-based organic dyes were conveniently prepared and well characterized. The triphenylamine or carbazole moieties were bonded to the indole group acting as a potential electron donor, which can tune the HOMO and LUMO levels of the resultant dye, and another triphenylamine or carbazole group was linked to the pyrrole ring on the nitrogen atom, which was expected to suppress the aggregation of the dye in the solid state to some degree. These two dyes were utilized as dye sensitizers in dye-sensitized solar cells and demonstrated efficient photon-to-electron conversion properties. [ABSTRACT FROM AUTHOR]

We characterize the nature of the low-lying excited states in H-aggregated perylene bisimide (PBI) dyes in terms of the recently proposed long-range-corrected density functional theory (LRC-DFT) and the mixed intramolecular Frenkel exciton (FE) and the intermolecular charge-transfer exciton (CTE) model. The singlet vertical excitation energies of H-aggregated PBI dimers and multimers are theoretically evaluated by considering the aggregation details. It is found that the dimer absorption follows closely the spectra of PBI aggregates in solution and demonstrates strong mixing of two kinds of excitons. The experimentally observed low-energy absorption peak near 2.3 eV should not be a pure CT state but a mixed excitonic state. To model the electronic excitations of H-aggregated PBI multichromophoric oligomers, we adopt a mixed FE-CTE model Hamiltonian, whose microscopic parameters are determined from LRC-DFT/TD-LRC-DFT calculations performed on an individual chromophore or a chromophore pair. By involving four to five PBI chromophores, we have succeeded in reproducing the experimental trends of optical properties in PBI stacking, such as the large blue shift of the absorption band, the mixed FE-CTE nature of the low-energy absorption bands, and the large Stokes shift of emission spectra. The long-range correction on DFT exchange-correlation energy functionals is crucial to correctly evaluate the photophysical characteristics of π−π stacks. [ABSTRACT FROM AUTHOR]

The interaction of anionic micelle sodium dodecyl sulfate (SDS) and amphiphilic block copolymers polyethylene-b-polyethylene glycol (PE-b-PEG) and the sharp change of excited-state charge-transfer complex photophysics of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide (DASPMI) inside of the supramolecular assembly have been addressed in the paper. The dramatic enhancement of emission intensity of DASPMI incorporated inside of the nanostructure formed by micellar and polymeric chains indicates a completely different environment compared to that in the water and micellar system. A huge increase in the rotational relaxation time obtained from time-resolved anisotropy decay and the value of the order parameter is indicative of a very restrictive regime in the self-assembly system. The wobbling and translational motion of the probe is also restricted inside of the micelle−polymer aggregate due to the presence of polymer chains. The translational diffusion coefficient is drastically reduced due to the aggregation. [ABSTRACT FROM AUTHOR]

A new organic fluorescent dye, 2,4-dichloro-6-[p-(N,N-diethylamino)biphenylyl]-1,3,5-triazine (DBQ), with an electron withdrawing−donating pair bridged by a twistable aromatic chain has been synthesized. DBQ exhibits high fluorescence quantum yields (0.96 in hexane and 0.71 in THF), high extinction coefficients, and an excitation window extending up to ∼480 nm. Due to the strong intramolecular charge transfer character, DBQ shows obviously solvent-dependent Stokes shifts with a value as high as 6360 cm−1in THF and controllable fluorescence emission in the visible region from “blue” to “orange”. The axially chiral structures of DBQ crystals were clearly revealed by the X-ray analyses and CD spectroscopy measurements. Two enantiomers of DBQ were obtained by spontaneous resolution upon crystallization without any chiral auxiliary. The low rotation barriers around the interannular bonds in DBQ molecules resulted in an efficient and selective multiplication of each of the chiral structures when DBQ crystallized in THF at room temperature in the presence of an enantiopure crystal seed, leaving racemized DBQ molecules in the solution. The special crystalline properties of DBQ provided a new approach to the design and synthesis of organic chiral crystals. The photophysical properties of DBQ make it promising in the preparation of new fluorescent probes with high sensitivity. [ABSTRACT FROM AUTHOR]

We have characterized the structure of J-aggregate in a Langmuir−Blodgett film of pure merocyanine dye (MS18) fabricated under an aqueous subphase containing a cadmium ion (Cd2+) and have investigated its thermal behavior by UV−visible and IR absorption spectroscopy in the range from 25 to 250 °C with a continuous scan. The results of both UV−visible and IR absorption spectra indicate that temperature-dependent changes in the MS18aggregation state in the pure MS18system are closely and mildly linked with the MS18intramolecular charge transfer and the behavior of the packing, orientation, conformation, and thermal mobility of MS18hydrocarbon chain, respectively. The J-aggregate in the pure MS18system dissociates from 25 to 150 °C, and the dissociation temperature at 150 °C is higher by 50 °C than that in the previous MS18-arachidic acid (C20) binary system. The lower dissociation temperature in the binary system originates from the fact that temperature-dependent structural disorder of cadmium arachidate (CdC20), being phase-separated from MS18, has an influence on the dissociation of J-aggregate. From 160 to 180 °C, thermally induced blue-shifted bands, caused by the oligomeric MS18aggregation, appear at around 520 nm in the pure MS18system by contraries, regardless of the lack of driving force by the melting phenomenon of CdC20. The temperature at which the 520 nm bands occur is in good agreement with the melting point (160 °C) of hydrocarbon chain in MS18with Cd2+, whereas its chromophore part is clearly observed to melt near 205 °C by UV−visible spectra. Therefore, it is suggested that the driving force that induces the 520 nm band in the pure MS18system arises from the partial melting of hydrocarbon chain in MS18with Cd2+. [ABSTRACT FROM AUTHOR]

The catalytic degradation of organic dye (methylene blue, MB) has been studied using green oxidation methods (tertiary-butyl hydrogen peroxide, TBHP, as the oxidant with several doped mixed-valent and regular manganese oxide catalysts in water) at room and higher temperatures. These catalysts belong to a class of porous manganese oxides known as octahedral molecular sieves (OMS). The most active catalysts were those of Mo6+- and V5+-doped OMS. Rates of reaction were found to be first-order with respect to the dye. TBHP has been found to enhance the MB decomposition, whereas H2O2does not. Reactions were studied at pH 3−11. The optimum pH for these reactions was pH 3. Dye-decomposing activity was proportional to the amount of catalyst used, and a significant increase in catalytic activity was observed with increasing temperature. X-ray diffraction (XRD), energy dispersive spectroscopy (EDX), and thermogravimetric analysis (TGA) studies showed that no changes in the catalyst structure occurred after the dye-degradation reaction. The products as analyzed by electrospray ionization mass spectrometry (ESI-MS) showed that MB was successively decomposed through different intermediate species. [ABSTRACT FROM AUTHOR]

A theoretical analysis, based on density functional theory, has been carried out on the electronic properties of eosin yellowish (2′,4′,5′,7′-tetrabromofluorescein), a dye used for photovoltaic applications. In particular different oxidation states of the bare molecule as well as its complexes with a Zn dication have been considered, with the aim to gain some insights on its electro- and photochemical behavior. The calculations have been carried out both in the gas phase and in solution, this last modeled by a continuum model. Besides the agreement with the experimental data, our results allow for a better interpretation of the spectroscopic properties of this dye and their tuning by interaction with the solvent or metal atom in aqueous solution. [ABSTRACT FROM AUTHOR]

Perylene-3,4:9,10-bis(dicarboximide) (PDI) and its derivatives are robust organic dyes that strongly absorb visible light and display a strong tendency to self-assemble into ordered aggregates, having significant interest as photoactive materials in a wide variety of organic electronics. To better understand the nature of the electronics states produced by photoexcitation of such aggregates, the photophysics of a series of covalent, cofacially oriented, -stacked dimers and trimers of PDI and 1,7-bis(3‘,5‘-di-t-butylphenoxy)perylene-3,4:9,10-bis(dicarboximide) (PPDI) were characterized using both time-resolved absorption and fluorescence spectroscopy. The covalent linkage between the chromophores was accomplished using 9,9-dimethylxanthene spacers. Placing n-octyl groups on the imide nitrogen atoms at the end of the PDI chromophores not attached to the xanthene spacer results in PDI dimers having near optimal -stacking, leading to formation of a low-energy excimer-like state, while substituting the more sterically demanding 12-tricosanyl group on the imides causes deviations from the optimum that result in slower formation of an excimer-like excited state having somewhat higher energy. By comparison, PPDI dimers having terminal n-octyl imide groups have two isomers, whose photophysical properties depend on the ability of the phenoxy groups at the 1,7-positions to modify the stacking of the PPDI molecules. In general, disruption of optimal -stacking by steric interactions of the phenoxy side groups results in excimer-like states that are higher in energy. The corresponding lowest excited singlet states of the PDI and PPDI trimers are dimer-like in nature and suggest that structural distortions that accompany formation of the trimers are sufficient to confine the electronic interaction on two chromophores within these systems. This further suggests that it may be useful to build into oligomeric PDI and PPDI systems some degree of flexibility that allows the structural relaxations necessary to promote electronic interactions between multiple chromophores. [ABSTRACT FROM AUTHOR]

New organic dyes composed of the benzo[b]furan donor, thiophene-conjugated bridge, and cyano acrylic acid acceptor have been newly synthesized through the one-pot coupling cyclization key step. Nanocrystalline TiO2 dye-sensitized solar cell was fabricated using this dye. A solar-to-electric conversion efficiency of 6.65% and 4.70% is achieved with 1 and 2, respectively. [ABSTRACT FROM AUTHOR]

The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion. The time course of formation of J-aggregates is described in most cases by a sigmoidal curve, and the kinetics and mechanism are discussed within the framework of autocatalysis. Computer simulations reveal that the sigmoidal time dependence is transferred to an exponential-like curve by substantially increasing the rate constant for the noncatalytic step. The reaction pathway into J-aggregates can be switched from dimeric ion pairs as the reactant to monomeric ion pairs, when the rate constant for the catalytic step via the monomer becomes larger with respect to that via the dimer. [ABSTRACT FROM AUTHOR]