Spectral,kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar media

Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10^?3 mol dm^?3. At low surfactant concentration (<5 × 10^?3 mol dm^?3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye–surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (K_A) for the formation of dye–SDS complex and the binding constant (K_B) for the micellization of dye are determined. Stopped‐flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629–636, 2003     

Neue Dimethinmerocyanin-Farbstoffe mit der (Sulfobutyl)benzothiazol-Gruppe als Donor-Teilchromophor und deren Aggregationsverhalten in wässriger Lösung

Novel Dimethinemerocyanine Dyes with the (Sulfobutyl)benzothiazole Group as Donor Part of the Chromophor and their Aggregation Tendency in Aqueous Solution A series of novel dimethinemerocyanine dyes with the (sulfobutyl)benzothiazole group as the donor part of the chromophor is synthesized in good yield and their aggregation tendency in H₂O without addition of salt investigated. The merocyanine dye 2b only gives J-aggregation in H₂O. The dyes 1a–f and 2a exhibit an intense, red-shifted absorption band due to J-aggregation in H₂O in the presence of Me₄NCl. In contrast, the dyes 1g and 2c–f show a slightly red-shifted absorption band. The degree of aggregation in H₂O is investigated by ultracentrifugation of the representative 2e . Indeed, the slightly red-shifted absorption band in H₂O is due to aggregation of ‘oligomers’ of the dye. Contrary to the aggregation of ‘polymers’ of dyes (J-aggregation), we suggest the term ‘K’ band for the slightly red-shifted absorption band. The hemicyanine dye 5 gives the same absorption band in MeOH and in MeOH/H₂O 1:3. The dye 11 shows an absorption band in H₂O that is probably blue-shifted because of negative solvatochromism. The merocyanine dye 13 gives H-aggregation in H₂O.     

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study

The absorption spectra of styrylbenzothiazolium dye derivatives were calculated by the time-dependent density functional (TD DFT) method. The dyes of interest were (p-dimethylamino)styrylbenzothiazolium dye and its protonated form as well as aza-15(18)-crown-5(6)-containing dyes and their complexes with alkali (K⁺ and Na⁺) and alkaline-earth (Ca²⁺, Sr²⁺, and Ba²⁺) cations. Several low-lying conformers of the azacrown-containing dyes were considered. The electronic and geometric structures of the excited states responsible for the appearance of the long-wave (π-π*) absorption bands are studied. Complexation causes a hypsochromic shift of the long-wave absorption band correlating with the pyramidality of the crown ether nitrogen in the complex. The interaction of the cation with 3–4 solvent molecules or a counterion (ClO₄ ^?) considerably reduces this shift, especially in the conformers without the metal-nitrogen bond. In some cases, the long-wave absorption band is close to the absorption band of the free dye. Similar results were obtained using the polarizable continuum model of solvation. Excited-state structures of the free model dye and the free azacrown-containing dyes exhibit a tendency to bond alternation. Conversely, the cationic complexes of the crown-containing dyes and the protonated model dye exhibit a tendency to bond equalization in the excited state. The changes in the excited-state geometries of the free dyes and their complexes account for the complexation-induced fluorescence enhancement observed in the experiments.     

Neue Sulfobutyl-haltige Bis(dimethinmerocyanin)-Farbstoffe mit isolierten Chromophoren im Molekül und deren Aggregationsverhalten in wässeriger Lösung

Novel Bis(dimethinemerocyanine) Dyes with Isolated Chromophores in the Molecule Containing the Sulfobutyl Group and their Aggregation Tendency in Aqueous Solution The bis(dimethinemerocyanine) dyes 7a – c with Chromophores separated by a polymethylene chain as ‘isolator’ are synthesized in good yield. Their aggregation tendency in organic solvents, organic solvents/H₂O mixtures, and in H₂O is investigated. In organic solvents, the dyes 7a – b show a splitted absorption band, due to interaction of the two Chromophores of the dye. In H₂O, 7a exhibits an intense absorption band at 496 nm (? = 224 300 1·mol^?1·cm^?1) with a small width $ (\tilde v_{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{$2$}}} = 1000\;{\rm cm}^{ - 1}) $ and shoulders at 552 and 580 nm. In presence of starch, this absorption band shifts to 617 nm, probably due to J-aggregation. The dye 7b shows the same spectral behaviour as 7a . In contrast, 7c exhibits an absorption band without splitting in organic solvents; the interaction of the Chromophores has disappeared. In H₂O and in H₂O containing starch, 7c shows a wide absorption band, due to interaction of the Chromophores of the dye.     

The electronic structures and spectra of proflavine,acridine orange,and their DNA complexes

The electronic structure of the proflavine cation is studied by the SCF –ASMO –CI method using the Pariser–Parr–Pople approximations. It is shown that the band at 445 mμ may be assigned to the ¹A₁ → ¹B₁, transition polarized along the long axis of the molecule. The bands in the neighbourhood of 260 mμ, which are composed of three absorption bands, are tentatively assigned to the ¹A₁ → ¹B₁, ¹A₁ → ¹B₁, and ¹A₁ → ¹A₁ transitions, respectively, in order of decreasing wavelength. The spectrum of the acridine orange cation may be understood to have the same assignment as that of the proflavine cation. The acridine dye cations are well known for their dimerization with concentration. The intermolecular distances in these dimers are estimated from the band shifts due to the formation of dimers, using the exciton theory. The main contribution to the molecular interaction is shown to be the electrostatic dipole–dipole interaction. Since the first excitation band of the dye molecule which exhibits a remarkable change due to the formation of the DNA–acridine dye complex, is suggested to be polarized along the long axis, preference of the outside stacking or the intercalation model is qualitatively discussed from the spectral shift of the acridine dye bound to the DNA, assuming simple models.     

Synthesis and specific solvatochromism of D–π–A type pyridinium dye

Donor–π–acceptor (D–π–A) type pyridinium dye bearing an iodide ion as the counter anion that has been newly synthesized showed specific solvatochromism, leading to large bathochromic shift of absorption band in halogenated solvents: the bathochromic shifts of the D–π–A type pyridinium dye in halogenated solvents are larger than those of the non-halogenated solvents of low ?_r values. Investigation of absorption spectral measurement, ¹H NMR measurements, and semi-empirical molecular calculations (AM1 and INDO/S using the SCRF Onsager Model) revealed that the intramolecular charge transfer (ICT) characteristics of the D–π–A type pyridinium dye became stronger in the halogenated solvents. On the basis of the experimental results and the theoretical calculations, the influences of halogenated solvent on the large bathochromic shift of D–π–A type pyridinium dye are discussed. ^©2012 Elsevier Science. All rights reserved.     

Spectroscopy of the E band of SO2 with a frequency-doubled single-mode dye laser

The rotational structure of the E band of SO₂ between 32720 and 32900 cm^?1 has been investigated by absorption spectroscopy with reduced Doppler width in a cooled cell at 190 K using a frequency-doubled cw single-mode dye laser. More than 400 lines in this band could be assigned, starting from a former partial analysis by Hamada and Merer. Severe perturbations in the upper state impede the assignment and prevent the unambiguous identification of many other lines in the spectrum. From the measured lines term values and molecular constants of the upper levels are derived. A comparison with spectra of very high resolution, taken in a collimated supersonic SO₂ beam demonstrates that the actual line density is by far higher than the spectral resolution in the cooled cell.     

The two-photon phosphorescence excitation spectrum of triphenylene

The two-proton excited phosphorescence of triphenylene in PMMA matrix at 77 K was measured using a tunable flashlamp-pumped rhodamine dye laser in the effect spectral region 32000–36000 cm^?1. The band origin of the S₀S₂ transition, which is uncertain in the one-photon absorption spectrum, was observed at 33200 cm^?1. The vibronic features in the one-photon spectrum were reinterpreted.     

On the lower excited electronic states of glyoxal

The polarization of both nπ* absorption bands of glyoxal has been measured in a glass matrix of 2-methyltetrahydrofuran by the photoselection method. The second absorption band in the 30 000 cm^?1 region has been assigned to a ¹A_g → ¹B_g nπ* transition. Its intensity is mainly induced by interaction with the solvent. An absorption band at about 43 000 cm^?1 has been ascribed to a charge transfer transition in complexes of glyoxal and 2-MTHF.     

The brilliant blue FCF ion-molecular forms in solutions according to the spectrophotometry data

The brilliant blue FCF acid–base properties in aqueous solutions have been studied and its ionization constants have been defined by tristimulus colorimetry and spectrophotometry methods. The scheme of the acid–base dye equilibrium has been proposed and a diagram of the distribution of its ionic-molecular forms has been built. It has been established that the dominant form of the dye was the electroneutral form, which molar absorptivity (ε₆₂₅ = 0.97 × 10⁵) increases with the increase of the dielectric permittivity of the solvent. It has been shown that the replacement of polar solvents by less polar ones is causing a bathochromic shift of the maximum absorption band of the dye, the value of which is correlated with the value of the Hansen parameter. Tautomerization constants have been defined in a number of solvents and associated with the value of the Dimroth-Reichardt parameter.     

Assessment of Luminescent Downshifting Layers for the Improvement of Light‐Harvesting Efficiency in Dye‐Sensitized Solar Cells

Luminescence downshifting (LDS) of light can be a practical photon management technique to compensate the narrow absorption band of high‐extinction‐coefficient dyes in dye‐sensitized solar cells (DSSCs). Herein, an optical analysis on the loss mechanisms in a reflective LDS (R‐LDS)/DSSC configuration is reported. For squaraine dye (550–700 nm absorption band) and CaAlSiN₃:Eu²⁺ LDS material (550–700 nm emission band), the major loss channels are found to be non‐unity luminescence quantum efficiency (QE) and electrolyte absorption. By using an ideal LDS layer (QE=100 %), a less absorbing electrolyte (Co‐based), and antireflection coatings, approximately 20 % better light harvesting is obtained. If the absorption/emission band of dye/LDS is shifted to 800 nm, a maximal short‐circuit current density (J_sc) of 22.1 mA cm^?2 can be achieved. By putting the LDS layer in front of the DSSC (transmissive mode), more significant loss channels are observed, and hence a lower overall efficiency than the R‐LDS configuration.     

Quantum chemical studies on structures and spectra of 2,5-distyrylpyrazine (DSP) laser dye

Semiempirical (MNDO and PM3) molecular orbital calculations have been undertaken to study the structures of the ground and excited states of 2,5-distrylpyrazine dye to assess its activity as a laser dye. In the ground and first excited singlet states, the trans-trans structure of C_2h symmetry is the most stable structure in the gas phase and in DMSO, which agrees with the experimental findings. Upon excitation, the flexibility of the molecule decreases, leading to a subsequent decrease in the radiationless deactivation pathway and this increases the fluorescence efficiency of DSP. The absorption, excitation, and emission spectra have been calculated at the MNDO level using the PM3 optimized geometries in DMSO. At this level the agreement between theory and experiment is quite good. An estimated absorption band at 377 nm (expt 380 nm) is assigned to the S₀→S₁ transition. The excited state absorption band at 457 nm (expt 460 nm) is assigned to the S₁→S₁₂ transition. The emission band at 458 nm (expt 460 nm) is assigned to the S′₁→S′₀ transition. The overlap between the emission and the excited-state absorption spectra is presumably the main reason behind the reduced laser activity of the investigated dye. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 585–592, 1998     

CdS‐Encapsulated TiO2 Nanotube Arrays Lidded with ZnO Nanorod Layers and Their Photoelectrocatalytic Applications

A novel TiO₂ nanotube array/CdS nanoparticle/ZnO nanorod (TiO₂ NT/CdS/ZnO NR) photocatalyst was constructed which exhibited a wide‐absorption (200–535 nm) response in the UV/Vis region and was applied for the photoelectrocatalytic (PEC) degradation of dye wastewater. This was achieved by chemically assembling CdS into the TiO₂ NTs and then constructing a ZnO NR layer on the TiO₂ NT/CdS surface. Scanning electron microscopy (SEM) results showed that a new structure had been obtained. The TiO₂ NTs looked like many “empty bottles” and the ZnO NR layer served as a big lid. Meanwhile the CdS NPs were encapsulated between them with good protection. After being sensitized by the CdS NPs, the absorption‐band edge of the obtained photocatalyst was obviously red‐shifted to the visible region, and the band gap was reduced from its original 3.20 eV to 2.32 eV. Photoelectric‐property tests indicated that the TiO₂ NT/CdS/ZnO NR material maintained a very high PEC activity in both the ultraviolet (UV) and the visible region. The maximum photoelectric conversion efficiencies of TiO₂ NT/CdS/ZnO NR were 31.8 and 5.98 % under UV light (365 nm) and visible light (420–800 nm), respectively. In the PEC oxidation, TiO₂ NT/CdS/ZnO NR exhibited a higher removal ability for methyl orange (MO) and a high stability. The kinetic constants were 1.77×10^?4 s^?1 under UV light, which was almost 5.9 and 2.6 times of those on pure TiO₂ NTs and TiO₂ NT/ZnO NR, and 2.5×10^?4 s^?1 under visible light, 2.4 times those on TiO₂ NT/CdS.     

BiVO4‐TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method

Composite photocatalyst films have been fabricated by depositing BiVO₄ upon TiO₂ via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP‐OES), XPS, photoluminescence and Mott–Schottky analyses. SILAR processing was found to deposit monoclinic‐scheelite BiVO₄ nanoparticles onto the surface, giving successive improvements in the films′ visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO₄ conduction band and valence band lying cathodically shifted from those of TiO₂. The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo‐first‐order rate constant of 0.004 min^?1. As a reference material, the same SILAR modification has been made to an inactive wide‐band‐gap ZrO₂ film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO₄–ZrO₂ system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self‐sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst′s conduction band.     

Cofluorescence of dyes in nanoparticles from metal ion complexes with diketones

Nanoparticles (NPs) from diketonates of Al³⁺, Sc³⁺, In³⁺ and Ln³⁺ doped with dye molecules are synthesized. The appearance of sensitized fluorescence (cofluorescence) of dye molecules due to energy transfer from the ensemble of complexes forming NPs is revealed in aqueous solutions of these NPs. It is shown that the dye cofluorescence in NPs from Eu complexes occurs as a result of two distinct processes of energy transfer (ET) to dye molecules: from singlet levels of ligands and from Eu³⁺ ions. It is found that the efficiency of ET from Eu³⁺ ions to dyes in NPs from Eu(DBM)₃phen is one order of magnitude higher than the efficiency of ET from S₁-levels of ligands to dyes in NPs from Al complexes with the same ligands. It is shown that the excitation of dye molecules through ligands of NPs results in the enhancement of the intensity of their fluorescence by a factor of 1.5–2 orders of magnitude compared to the excitation of their own first band of absorption.     

Constructing Organic D–A–π‐A‐Featured Sensitizers with a Quinoxaline Unit for High‐Efficiency Solar Cells: The Effect of an Auxiliary Acceptor on the Absorption and the Energy Level Alignment

Four organic D–A –π‐A‐featured sensitizers (TQ1, TQ2, IQ1, and IQ2) have been studied for high‐efficiency dye‐sensitized solar cells (DSSCs). We employed an indoline or a triphenylamine unit as the donor, cyanoacetic acid as the acceptor/anchor, and a thiophene moiety as the conjugation bridge. Additionally, an electron‐withdrawing quinoxaline unit was incorporated between the donor and the π‐conjugation unit. These sensitizers show an additional absorption band covering the broad visible range in solution. The contribution from the incorporated quinoxaline was investigated theoretically by using DFT and time‐dependent DFT. The incorporated low‐band‐gap quinoxaline unit as an auxiliary acceptor has several merits, such as decreasing the band gap, optimizing the energy levels, and realizing a facile structural modification on several positions in the quinoxaline unit. As demonstrated, the observed additional absorption band is favorable to the photon‐to‐electron conversion because it corresponds to the efficient electron transitions to the LUMO orbital. Electrochemical impedance spectroscopy (EIS) Bode plots reveal that the replacement of a methoxy group with an octyloxy group can increase the injection electron lifetime by a factor of 2.4. IQ2 and TQ2 can perform well without any co‐adsorbent, successfully suppress the charge recombination from TiO₂ conduction band to I₃^? in the electrolyte, and enhance the electron lifetime, resulting in a decreased dark current and enhanced open circuit voltage (V_oc) values. By using a liquid electrolyte, DSSCs based on dye IQ2 exhibited a broad incident photon‐to‐current conversion efficiency (IPCE) action spectrum and high efficiency (η=8.50 %) with a short circuit current density (J_sc) of 15.65 mA cm^?2, a V_oc value of 776 mV, a fill factor (FF) of 0.70 under AM 1.5 illumination (100 mW cm^?2). Moreover, the overall efficiency remained at 97 % of the initial value after 1000 h of visible‐light soaking.     

Modulation of Excited‐State Proton Transfer of 2‐(2′‐Hydroxyphenyl)benzimidazole in a Macrocyclic Cucurbit[7]uril Host Cavity: Dual Emission Behavior and pKa Shift

The effect of the macrocyclic host, cucurbit[7]uril (CB7), on the photophysical properties of the 2‐(2′‐hydroxyphenyl)benzimidazole (HPBI) dye have been investigated in aqueous solution by using ground‐state absorption and steady‐state and time‐resolved fluorescence measurements. All three prototropic forms of the dye (cationic, neutral, and anionic) form inclusion complexes with CB7, with the largest binding constant found for the cationic form (K≈2.4×10⁶ M ^?1). At pH≈4, the appearance of a blue emission band upon excitation of the HPBI cation in the presence of CB7 indicates that encapsulation into the CB7 cavity retards the deprotonation process of the excited cation, and hence reduces its subsequent conversion to the keto form. Excitation of the neutral form (pH≈8.5), however, leads to an increase in the keto form fluorescence, indicating an enhanced excited‐state intramolecular proton‐transfer process for the encapsulated dye. In both the ground and excited states, the two pK_a values of the HPBI dye show upward shifts in the presence of CB7. The prototropic equilibrium of the CB7‐complexed dye is represented by a six‐state model, and the pH‐dependent changes in the binding constants have been analyzed accordingly. It has been observed that the calculated pK_a values using this six‐state model match well with the values obtained experimentally. The changes in the pK_a values in the presence of CB7 have been corroborated with the modulation of the proton‐transfer process of the dye within the host cavity.     

Visible light photodegradation of rhodamine B over VDF/CTFE copolymer-templated crystalline mesoporous titania

Mesoporous TiO₂ with anatase crystalline structure (MTiO₂/F₂₃₁₉) has been synthesized by using vinylidene fluoride/chlorotrifluoroethylene copolymer (1:9 in mole, F₂₃₁₉) as template. The synthesized mesoporous titania samples were characterized by a combination of various physicochemical techniques, such as X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and N₂ adsorption/desorption. It was found that without any external doping, MTiO₂/F₂₃₁₉ exhibited significantly higher photocatalytic activities for the degradation of rhodamine B (RhB) dye than P25 TiO₂ under visible light irradiation. Furthermore, the UV-Vis absorption maximum of the dye solution exhibited a gradual hypsochromic shift due to de-ethylation and degradation of RhB dye.     

Synthesis, structure, UV-Vis-IR spectra, magnetism and theoretical studies on Cu[(2-aminomethyl)pyridine](thiocyanate)2 and comparisons with an analogous Cu complex

The title complex was synthesized under self-assembly conditions using Cu(acetate)₂·H₂O, 2-amp (= 2-aminomethylpyridine) and KSCN, and was characterized by IR, elemental analysis and single crystal structural analysis, and its spectral and RT magnetic properties were investigated. The asymmetric unit consists of a square planar Cu(II) center, with two ligand N atoms and two anionic Ns forming the square plane. In the unit cell, the monomeric complex assembles into 2-D layers through very weak non-bonded interactions between anionic S and Cu²⁺. Further, the structure was satisfactorily modeled by calculations based on Density Functional Theory (DFT), and the UV-Vis and IR spectra are analyzed in depth with the help of Time Dependent DFT (TDDFT). The results indicate that the absorption maxima are at relatively high energy and are mainly assigned to π → π^∗ transitions (in pyridine), with a fair contribution of metal to ligand charge transfer (MLCT) and ligand to ligand charge transfer (LLCT) transitions. All the low lying transitions are categorized as mixed MLCT/LLCT. A very weak but broad band in the higher wavelength region has been detected and identified as a d-d transition band. Also, it has been found that when the ligand ratio is modified, the formation of Cu(2-amp)₂(SCN)₂ takes place under the same self-assembly conditions, whose structure only has been recently reported. Structural, spectral and theoretical comparisons are presented for both complexes.     

Self-assembly and optical properties of N N′-bis(4-(1-benzylpiperidine))perylene-3,4,9,10-tetracarboxylic diimide

Well-defined nanobelts with strong fluorescence were fabricated from a perylene tetracarboxylic diimide molecule modified with specific side-chain substitution. The new perylene diimide was characterised by ¹H, ¹³C NMR, mass and IR spectral techniques. The photophysical and electrochemical properties were investigated by UV–vis absorption, fluorescence, differential scanning calorimetry and cyclic voltammetry. 1D nanobelt self-assembly of the compound was studied with optical, fluorescence and scanning electron microscopic techniques. The observed self-assembly was supported by computational studies using density functional theory and natural bond order analysis. The optimised molecule was fit into crystal space theoretically, and the observed band gap was correlated well with optical and electrical properties.