Electronic absorption spectra of cresyl violet acetate in anisotropic and isotropic solvents

Axial H-Bonding Solvent Controls Inhomogeneous Spectral Broadening, While Peripheral H-Bonding Solvent Controls Vibronic Broadening: Cresyl Violet in Methanol

The dynamics of the nuclei of both a chromophore and its condensed-phase environment control many spectral features, including the vibronic and inhomogeneous broadening present in spectral line shapes. For the cresyl violet chromophore in methanol, we here analyze and isolate the effect of specific chromophore-solvent interactions on simulated spectral densities, reorganization energies, and linear absorption spectra. Employing both chromophore and its condensed-phase environment control many spectral features, including the vibronic and inhomogeneous broadening present in spectral line shapes. For the cresyl violet chromophore in methanol, we here analyze and isolate the effect of specific chromophore-solvent interactions on simulated spectral densities, reorganization energies, and linear absorption spectra. Employing both force field and ab initio molecular dynamics trajectories along with the inclusion of only certain solvent molecules in the excited-state calculations, we determine that the methanol molecules axial to the chromophore are responsible for the majority of inhomogeneous broadening, with a single methanol molecule that forms an axial hydrogen bond dominating the response. The strong peripheral hydrogen bonds do not contribute to spectral broadening, as they are very stable throughout the dynamics and do not lead to increased energy-gap fluctuations. We also find that treating the strong peripheral hydrogen bonds as molecular mechanical point charges during the molecular dynamics simulation underestimates the vibronic coupling. Including these peripheral hydrogen bonding methanol molecules in the quantum-mechanical region in a geometry optimization increases the vibronic coupling, suggesting that a more advanced treatment of these strongly interacting solvent molecules during the molecular dynamics trajectory may be necessary to capture the full vibronic spectral broadening.

Scaling Law for Kasha's Rule in Photoexcited Molecular Aggregates

We study the photophysics of molecular aggregates from a quantum optics perspective, with emphasis on deriving scaling laws for the fast nonradiative relaxation of collective electronic excitations, referred to as Kasha's rule. Aggregates exhibit an energetically broad manifold of collective states with delocalized electronic excitations originating from near-field dipole-dipole exchanges between neighboring monomers. Photoexcitation at optical wavelengths, much larger than the monomer-monomer average separation, addresses almost exclusively symmetric collective states, which for an arrangement known as H-aggregate show an upward hypsochromic shift. The extremely fast subsequent nonradiative relaxation via intramolecular vibrational modes populates lower energy, subradiant states, resulting in effective inhibition of fluorescence. Our analytical treatment allows for the derivation of an approximate scaling law of this relaxation process, linear in the number of available low-energy vibrational modes and directly proportional to the dipole-dipole interaction strength between neighboring monomers.

Construction of a highly sensitive detection platform for heparin based on a "turn-off" cationic fluorescent dye

A highly sensitive detection platform for heparin was constructed via the utilization of a commercially available cationic fluorescent dye (cresyl violet acetate, CV) as a fluorescence probe. The electrostatic binding between CV and heparin quenched the fluorescence in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic (HEPES) buffer solution (10 mM, pH 7.1). CV was highly selective towards heparin over other potential inferring substances. The detection limit of heparin detection was 5.19 ng/mL, and the linear working range was 0 ∼ 1 μg/mL in HEPES solution. In 1 % serum, the detection platform based on the fluorescence "turn-off" behavior of CV was also successfully constructed with a detection limit of 5.86 ng/mL in the linear range of 0 ∼ 0.8 μg/mL. Moreover, the CV-heparin complex was considered a potential sensor platform for the detection of protamine because of its stronger affinity for heparin and protamine.

Tunable induced circular dichroism in gels

The ICD phenomenon has drawn a lot of attention in recent years in applicable fields such as chiral sensing and chiroptical devices. In this work, we first gaze at the issues of thin spin-coated films not being able to deliver consistent ICD signals. A hypothesis of the underlying problem is proposed through a brief elucidation of the spin-coating process. To confirm and eliminate the uncontrollable dynamic factors with spin coating, we then dedicate our efforts to develop a new gel system based on chiral L-/D-N',N'-Dibenzoyl-cystine. Achiral dye molecules are intercalated in a DBC gel through a "one-step" preparation procedure. Compared to the former spin-coating system, significantly improved reproducibility of the new gel system is demonstrated. Besides, the ICD signals can be customized in a broad spectral range (wavelength tunability) by substituting dye molecules. Finally, we discuss the potential applications of this interesting system.

Computational Study of Cresyl Violet Covalently Attached to the Silane Coupling Agents: Application to TiO2-Based Photocatalysts and Dye-Sensitized Solar Cells

The covalent attachment of photosensitizing dyes to TiO₂ using silane coupling agents (SCAs) is a promising strategy for enhancing the photocatalytic activity of TiO₂-based photocatalysts and the photovoltaic conversion of dye-sensitized solar cells (DSSCs). This approach can control the geometry and orientation of the photosensitizing dye on the TiO₂ surface. In this study, a density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation was carried out on cresyl violet (CV) covalently attached to SCAs with a terminal oxirane group (OTES–Cn) to reveal the influence of OTES–Cn on the geometry of the photosensitizing dyes. The potential of CV covalently attached to OTES–Cn (CV–OTES–Cn) to act as a photosensitizing dye was also analyzed. The hydroxyl group formed by the epoxy-opening reaction between CV and OTES–Cn strongly influenced the geometry of CV–OTES–Cn, which was attributed to a CH–O interaction. Additionally, TD-DFT, frontier molecular orbital and molecular electrostatic potential calculations revealed that CV–OTES–Cn has excellent optical properties and electron injection ability. In particular, the characteristics of the unbent conformation of CV–OTES–Cn are expected to contribute significantly to the photocurrent in TiO₂-based photocatalysts and DSSCs. These findings enhance the understanding of the covalent attachment strategy using SCAs and contribute to improving TiO₂-based photocatalysts and DSSCs.

Competitive Binding of Organic Dyes between Cucurbiturils and Octa Acid

Employing six cationic water-soluble organic dye molecules as probes, we have attempted to qualitatively understand the factors that govern the attraction between such molecules and the anionic water-soluble host, octa acid (OA). Examination of the competitive host-guest complexation between cucurbit[8]uril (CB[8]) and OA using absorption and emission spectroscopy revealed that the dye molecules included within CB[8] could be "pulled out" by OA. However, an order of magnitude higher concentration of OA was required to shift the equilibrium toward OA, suggesting that attraction between the anionic host OA and the cationic dye molecules such as cresyl violet perchlorate and methylene blue is weaker than the hydrophobic and cation-dipolar interaction between these dye molecules and CB[8]. The importance of Coulombic attraction between OA and dye molecules is also revealed by monomer-to-dimer conversion upon addition of OA to an aqueous solution of monomeric dye molecules. Under conditions where the dye-to-OA ratio is high, freely dissolved monomeric dye molecules are attracted to the exterior of OA and aggregate as dimers on the exterior wall of OA. On the other hand, at high ratios of OA to dye molecules, the dye molecules adsorb as monomers on the exterior of OA. Thus, the monomer-to-dimer ratio in aqueous solution can be controlled by adjusting the ratio of dye to OA molecules. The results presented are of value in qualitatively understanding the relative binding properties of ionic guests with ionic hosts. Studies are qualitative in nature, and further detailed quantitative studies planned for the future are likely to provide deeper understanding of the interaction between water-soluble dye molecules, OA, and CB.

pH-Responsive diblock copolymers with two different fluorescent labels for simultaneous monitoring of micellar self-assembly and degree of protonation

Facile labelling of both blocks of a pH-responsive diblock copolymer with different fluorophores allows monitoring of polymer aggregation and deprotonation.

Novel oxazine and oxazone dyes: aggregation behavior and physicochemical properties

Novel compounds exhibited good properties in comparison with the corresponding starting reagent and satisfy the conditions of a potential drug.

Analytical and preparative chromatographic procedures for obtaining pure cresyl violet and cresyl red from commercial cresyl violet

Cresyl violet and cresyl red, components of commercial cresyl violet acetate, were separated and purified using preparative column liquid chromatography. The stationary phase was silica gel and gradient elution was carried out using chloroform:methanol. The purified dyes were obtained in high yield; 51% of the original lot was recovered as cresyl violet and 40% as cresyl red. Separated materials were characterized by nuclear magnetic resonance and mass spectroscopy; UV-visible and Fourier-transform infrared spectra also were obtained for samples of pure cresyl violet and cresyl red. The colored constituents of the commercial dye lot were identified using thin layer chromatography and reverse phase high performance liquid chromatography. Both methodologies were suitable for routine testing; reverse phase high performance liquid chromatography is an appropriate tool for quality control and high resolution identification of these compounds.

A comparative study on the aggregate formation of two oxazine dyes in aqueous and aqueous urea solutions

The visible absorption spectra of two oxazine dyes, brilliant cresyl blue and nile blue, in aqueous and aqueous urea solutions (0.01-1 M) were studied as a function of the dye concentration. Due to structural similarity of the investigated dyes, their spectral features were compared. The dimerization behavior of the dyes in water with or without urea was analyzed in terms of monomer-dimer equilibrium. The nature and structure of the interacting pairs for these dyes were discussed using the exciton theory. The dimerization constant values of the dyes in aqueous and aqueous urea solutions were calculated. For both the dyes in aqueous urea solutions, a reduction in dimer formation was observed. The excitonic parameters were compared with those of oxazine-1, which is structurally similar to the investigated dyes.

Dimeric spectra analysis in Microsoft Excel: a comparative study

The purpose of this work is to introduce the reader to an Add-in implementation, Decom. This implementation provides the whole processing requirements for analysis of dimeric spectra. General linear and nonlinear decomposition algorithms were integrated as an Excel Add-in for easy installation and usage. In this work, the results of several samples investigations were compared to those obtained by Datan.

Effect of polyacrylamide hydrophilic gel composition on photo-physical behavior of Oxazine 750

Electronic absorption spectra of Oxazine 750 dye in aqueous solutions and in polyacrylamide hydrogel matrix with different structural composition were studied at room temperature. The transport and the solute-solute interactions of the ionic dye in aqueous solutions across the hydrophilic gels were investigated via exploring spectral properties of the dye-loaded hydrogel. The nature of the dye pair interactions in these media was discussed using the Kasha exciton theory. In addition, the monomer-dimer equilibrium of Oxazine 750 in hydrogels with different compositional percentage has been determined by means of UV-vis spectroscopy and least square fitting methods.

Solvent polarizability and anisotropy effects on the photophysical behavior of oxazine 1: an appropriate polarizability indicator dye

The spectroscopic features of a laser dye, oxazine 1 (OX1), were investigated in liquid and in liquid crystalline solutions as a function of the solvent polarity and polarizability. The nature of spectral shift was investigated by studying the absorption spectra of the dye in different solvents. The spectral shifts were correlated by the solvent polarity and polarizability. As a result, the solvent polarity has no large and regular effect on the spectral behavior of the dye, and thus it might be considered as a poor solvatochromic dye. In contrast, an excellent linear correlation was observed between the solvent polarizability and the spectral properties of the dye, and therefore, this dye might be considered as a good indicator for measuring the solvent polarizability. The absorption and fluorescence spectra of the dye were investigated in nematic solvents with high birefringence. In nematic solvents, anisotropy of polarizability has a major contribution to the shaping of the absorbance and emission spectra of OX1.