Bengal Molecules Research Articles

Luminescence Spectral Characteristics of Markers of the Fluorescein Family in Reverse Micelles of Various Sizes

The luminescence spectral characteristics of eosin, erythrosine, and rose Bengal molecules in reverse micelles of sodium bis(2-ethylhexyl)sulfosuccinate were investigated. Inclusion of the dye molecules in the reverse micelles leads to an increase of their hydrodynamic radii Rh, and a linear relationship is observed between this increase ΔRh and the degree of hydration w. The increase of Rh leads to shift in the absorption and fluorescence spectra and increases the Stokes shift. The ratio of the dipole moments of the molecules in the excited and ground states μe/μg increases with increase of Rh.

On the interaction between up-converting NaYF4:Er3+,Yb3+ nanoparticles and Rose Bengal molecules constrained within the double core of multifunctional nanocarriers

The detailed analysis of interaction between up-converting nanoparticles and Rose Bengal photosensitizer allows for better understanding of energy transfer mechanisms with regards to more efficient near infrared triggered photodynamic therapy.

Improvement of Temperature-responsive Drug Release from Collagen-mimic Dendrimers

Abstract Gelatin, a thermally denatured collagen, forms a temperature-dependent gel, in which the efficiency of the collagen-like triple helix is dependent on temperature. In this study, (proline–hydroxyproline–glycine)n peptides were modified at the dendrimer to produce a type of collagen-mimic dendrimer. These dendrimers worked as a drug carrier with thermosensitive release capabilities and could retain rose bengal molecules stably.

Memory-Switching Phenomenon in Acceptor-Rich Organic Molecules: Impedance Spectroscopic Studies

We have studied memory-switching phenomena in terms of impedance spectroscopy in a series of xanthene-class fluorescein molecules. Frequency response studies have revealed that the electronic conduction mechanism was largely tuned by increasing the number of acceptor groups attached to the molecular backbone. In molecules with weak intermolecular interactions, the transition between a low- and a high-conducting state has been associated with a change in bulk resistance and dielectric properties. The devices in the two states remained a parallel combination of a resistor and a capacitor (C(P)-R(P)) network. In devices based on Rose Bengal, which exhibits a strong dipole-dipole interaction due to its acceptor groups, the switching between the states has been modeled as a transition between a C(P)-R(P) network in the off-state and a distributed resistor-capacitor (R-C) line network in the on-state. Instead of isolated clusters, a highly coupled network of reduced Rose Bengal molecules with strong dipole-dipole interaction yielded the high-conducting state. Under a "write-read-erase-read" sequence, the device switched between the two networks reversibly for many cycles.

Multilevel conductivity and conductance switching in supramolecular structures of an organic molecule

We have demonstrated conductance switching between multilevel states in devices based on Rose Bengal molecules embedded in supramolecular matrices. Two mechanisms, namely electroreduction and conformational change of the molecules, resulting in conjugation modification have been proposed to be applicable in these devices. In a low voltage region, reverse-bias induced electroreduction of Rose Bengal facilitated conjugation restoration in the backbone of the molecule and, hence, switching to a high-conducting state. At high biases, the two perpendicular planes present in Rose Bengal, which have permanent dipole moments, allowed forward-bias induced conformation change to occur, and results in conductance switching. We have demonstrated how the devices can switch between two pair of conducting states for random-access memory and read-only memory applications for several hours.

Tuning of Organic Reversible Switching via Self‐Assembled Supramolecular Structures

Single‐layer devices based on Rose Bengal show large conductance switching between the on and off states (on/off ratio = 104) in the pristine form. Rose Bengal molecules have been incorporated into different water soluble “host” polymer‐based supramolecular matrices by layer‐by‐layer electrostatic self‐assembly. Different ionic groups in the supramolecular structures tune the leakage current and the on/off ratio by several orders of magnitude. The switching devices may be used in random‐access and read‐only memory applications.

Photostability of xanthene molecules trapped in poly(vinyl alcohol) (PVA) matrices

Photobleaching reactions of fluorescein and Rose Bengal molecules dissolved in PVA matrices were studied as a function of the temperature. We used and compared two theoretical approaches to describe these photobleaching kinetics. Photobleaching quantum yield calculations were done using an adapted model (B-model) for polychromatic excitation that allowed us to estimate the average number of photons absorbed by each dye molecule before its bleaching. The other model uses exponential functions allowing us to calculate rate constants and activation energy. A slower photobleaching process was obtained for Rose Bengal sorbed in PVA matrices compared with fluorescein. We also obtained that the Rose Bengal photobleaching process is always single-exponential kinetic independent of the polymer relaxation process. Nevertheless, fluorescein photobleaching reaction is bi-exponential process at higher concentrations and it is strongly dependent on the polymer relaxation processes. These results were interpreted in terms of the different efficiencies among the processes involving quenching of the lowest triplet state.

Photoelectrochemical Properties of Dye-Sensitized TiO<sub>2</sub> Films Containing Dispersed Gold Metal Particles Prepared by Sol-Gel Method

Effects of gold nanoparticle incorporation on the photoanodic properties were studied for fluorescein-, rose bengal- and nile blue A-deposited TiO2 film electrodes prepared by the sol-gel method. The incorporation of gold particles decreased the dye-induced photoresponse in the visible region, which was ascribed to the retarded electron transport in the conduction band due to the Schottky barriers at titania/gold interfaces. The extent of decrease in photoresponse, however, was the smallest for the electrode sample with rose bengal, whose optical absorption well overlapped the surface plasma resonance of the gold particles. The dipole-dipole coupling between rose bengal molecules and gold particles was thought to enhance the photochemical processes, resulting in smaller reduction in the photoresponse.

FT-IR and Raman spectroscopy study of the amylose-Rose Bengal complex

FT-IR and Raman spectra of amylose-Rose Benagl in solution and in lyophilised samples were investigated. In the Rose Bengal molecule, the number and positions of active atoms, i.e., those that interact with amylose, were determined. The interaction with amylose was found not to affect the Rose Bengal quinonoidal structure. Results for the amylose complex show considerable hindrance of the rotational vibrations of amylose functional groups. Moreover, the influece of Rose Bengal on the infrared signals in the structuer-sensitive region (950–1200 cm −) was studied. The FT-IR results indicated the formation of a stiff amylose network induced by Rose Bengal molecules.

Aggregation of rose bengal molecules in solution

Abstract Absorption, emission and excitation spectral data support the thesis that rose bengal forms H-type aggregates in water and polar, protic solvents.

ChemInform Abstract: CIDNP STUDY OF QUENCHING PROCESSES OF EXCITED XANTHENE DYES BY AROMATIC AMINES

Strong proton nuclear polarization is produced by the quenching of excited triplet state Rose Bengal molecules by aromatic amines. In secondary amines significant polarization (but no permanent chemical change) is observed in the ring ortho and para protons and in the N-alkyl α methylene (or methyl) protons. In this case the operation of a highly reversible hydrogen atom transfer quenching mechanism is indicated. Tertiary aromatic amines give polarized unstable intermediates for which the perpendicular aromatic ring structure is suggested.

CIDNP study of quenching processes of excited xanthene dyes by aromatic amines

AbstractStrong proton nuclear polarization is produced by the quenching of excited triplet state Rose Bengal molecules by aromatic amines. In secondary amines significant polarization (but no permanent chemical change) is observed in the ring ortho and para protons and in the N‐alkyl α methylene (or methyl) protons. In this case the operation of a highly reversible hydrogen atom transfer quenching mechanism is indicated. Tertiary aromatic amines give polarized unstable intermediates for which the perpendicular aromatic ring structure is suggested.