Ab initio study of optical properties of rhodamine 6G molecular dimers

Fabrication and Fluorescence Analysis of Rhodamine Dyes in Polycarbonate Serpentine Microfluidic System

The synthesis of rhodamine dyes (R6G and R1010) and their fluorescence characterization within polymer-based microfluidics, offers an exciting and novel approach in materials science and chemical analysis. This work investigates the emission of polycarbonate substrates (PC) by UV-visible. The ablation threshold (16mj.sec-1) of PC at 193nm wavelength after that ablation process continued to produce microfluidic serpentine channels on PC by using G-Code. The fluorescence characteristics of Rhodamine 6G and Rhodamine 101 are investigated. Absorption and emission at peak wavelength were analyzed against R6G and R101 concentrations. Furthermore, the refractive indices of both R6G and R101 vis concentrations are examined. As a result at low concentrations, there was the highest overlapping, and at high concentrations, there was the smallest overlapping. R101 showed better photostability and a more consistent diffusion, whereas R6G had a faster diffusion and stronger fluorescence intensity. These differences were caused by the different molecular structures of the dyes and their interactions with the PC microchannel. Incorporating R6G and R101 dyes into a polycarbonate PC microfluidic chip would enhances both the resolution and sensitivity of fluorescence detection. The limited microfluidic setup facilitates ultra-high-resolution investigation and minimizing sample volumes, making it suitable for applications requiring precise measurements. The innovation relies on the utilization of the unique fluorescence characteristics of R6G (Rhodamine 6G) and R101 (Rhodamine 101) dyes to enhance the performance of polycarbonate microfluidic devices. R6G has high fluorescence quantum yield and stability, rendering it suitable for sensitive detection, while R101 offers superior brightness and improved resistance to photobleaching. Incorporation of these dyes into polymeric microfluidics improves sensitivity and facilitates real-time, dynamic sample analysis. This method offers a portable, economical solution with high-throughput capabilities, greatly enhancing both analytical and process accuracy across a variety of applications.

Reviewing the effect of aggregates in Rhodamine 6G aqueous solution on fluorescence quantum efficiency

Rhodamines constitute a class of dyes extensively investigated and applied in various contexts, primarily attributed to their high luminescence quantum yield. This study delves into the impact of aggregation on the thermal and optical properties of Rhodamine 6G (R-6G) solutions in distilled water. Examined properties encompass thermal diffusivity (D), temperature coefficient of the refractive index (dn/dT), fluorescence quantum efficiency (η), and energy transfer (ET). These parameters were assessed through thermal lens (TL) and conventional absorption and emission spectroscopic techniques. The dimerization of R-6G solutions was revisited, revealing that an increase in R-6G concentration alters the features of absorption and emission spectra due to dimer formation, resulting in unexpected behavior of η. Consequently, we introduce a novel model for the fraction of absorbed energy converted into heat (φ), which accounts for emissions from both monomers and dimers. Employing this model, we investigate and discuss the concentration-dependent behaviors of η for monomers (ηm) and dimers (ηd). Notably, our findings demonstrate that ηm values necessitate ηd = 0.2, a relatively substantial value that cannot be disregarded. Additionally, applying the Förster theory for dipole-dipole electric ET, we calculate microparameters for ET between monomers (CDD) and monomer-dimer (CDA). Critical ranges for ET in each case are quantified. Microparameter analysis indicates that ET between monomer-monomer and monomer-dimer species of R-6G dissolved in distilled water holds significance, particularly in determining ηm. These results bear significance, especially in scenarios involving high dye concentrations. While applicable to R-6G in water, similar assessments in other media featuring aggregates are encouraged.

Rapid determination of ethanol content based on an optical fiber-device and R6G-indicator

A rapid method for the determination of ethanol content is proposed and tested. A fluorescence detecting system, with a multimode fiber (MMF) sensing head, is employed. Rhodamine 6G (R6G) is applied as the fluorescent indicator. In the R6G aqueous solution, the molecules aggregate at high concentration, causing fluorescence quenching. Nevertheless, aggregation and quenching rarely occur in ethanol. Taking an ethanol and water mixture as the solvent, the photoluminescence (PL) intensity reflects the aggregation degree and the ethanol content. Based on this phenomenon, the contents of the ethanol-water mixture were measured through PL intensity detection. A limit of detection (LOD) at ∼0.1 vol% level was obtained in the range of 0-100%. Commercial Chinese baijiu and rubbing alcohol were tested and the results obtained were consistent with the label values. The detecting system is compact and of low-cost, and the detecting method is rapid, accurate and repeatable. There is good prospect of applications for the determination of ethanol content on-site.

Surface-Enhanced Raman Scattering (SERS) Studies of Disc-on-Pillar (DOP) Arrays: Contrasting Enhancement Factor with Analytical Performance

The use of nanomachining methods capable of reproducible construction of nano-arrayed devices have revolutionized the field of plasmonic sensing by the introduction of a diversity of rationally engineered designs. Significant strides have been made to fabricate plasmonic platforms with tailored interparticle gaps to improve their performance for surface-enhanced Raman scattering (SERS) applications. Over time, a dichotomy has emerged in the implementation of SERS for analytical applications, the construction of substrates, optimization of interparticle spacing as a means to optimize electromagnetic field enhancement at the localized surface plasmon level, and the substrate sensitivity over extended areas to achieve quantitative performance. This work assessed the enhancement factor of plasmonic Ag/SiO₂/Si disc-on-pillar (DOP) arrays of variable pitch with its analytical performance for quantitative applications. Experimental data were compared with those from finite-difference time-domain (FDTD) simulations used in the optimization of the array dimensions. A self-assembled monolayer (SAM) of benzenethiol rendered highly reproducible signals (RSD ∼4-10%) and SERS substrate enhancement factor (SSEF) values in the orders of 10⁶-10⁸ for all pitches. Spectra corresponding to rhodamine 6G (R6G) and 4-aminobenzoic acid demonstrated the advantages of using the more densely packed DOP arrays with a 160 nm pitch (gap = 40 nm) for quantitation in spite of the strongest SSEF was attained for a pitch of 520 nm corresponding to a 400 nm gap.

Removal of rhodamine 6G with different types of clay minerals

With an increased use of color dye in textile industries and elevated fabrics output, more scientific studies and technology developments are needed to effectively treat wastewater containing dyes. However, better understanding of the interactions between dyes and suspended solids is a necessity to advance such developments. In this study the interactions between rhodamine 6G (R6G), a cationic dye, and different types of clays minerals, commonly found in the wastewater sludge, were elucidated. The uptake of R6G on the clay minerals was attributed to cation exchange on the external surfaces of non-swelling clays, and at both external and interlayer spaces for swelling clays. In the interlayer of montmorillonite, the R6G molecules form monolayer and bilayer configurations under low and high uptake levels. The significant amounts of R6G uptake indicate that clay minerals are good sorbents for the removal of cationic dyes from water. And the R6G could be readily removed in wastewater treatment by adding small amount of clays and flocculated the clays out.

Tuning the spectral, morphological and photophysical properties of sonochemically synthesized poly(carbazole) using acid Orange, fluorescein and rhodamine 6G

The lifetimes and quantum yields of organic dyes are widely investigated due to their potential application in organic light emitting diodes (OLEDs). With a view to explore the possibility of enhancing the fluorescent properties of organic conjugated polymers such as polycarbazole, the present preliminary study reports for the first time, dye modification of polycarbazole using as acid orange (AO), fluorescein (Fluo) and Rhodamine 6G (R6G) for improving its fluorescence properties. The modification of PCz via doping was confirmed by FTIR, UV-visible, XRD and TEM analyses. The fluorescence studies and confocal microscopy were carried out both in solution and solid states to investigate the behavior of the dye modified PCz. Doping was found to be governed by the chemical structure of the dye. PCz-AO revealed intense doping which was confirmed by FTIR and UV-visible studies. PCz-Fluo and PCz-R6G exhibited the highest quantum yield and fluorescence emission in the solid state. Hence, by tailoring the structure of these conjugated polymers, stable fluorescence emitting materials can be designed for their potential application in OLEDs.

Asymmetric dendrimers with improved electro-optic performance: synthesis and characterization

A new series of electro-optical dendrimers with asymmetric configurations was synthesized through a Cu-(I) catalyzed Huisgen reaction.

Multi-channel lock-in amplifier assisted femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy with efficient rejection of superfluorescence background

Superfluorescence appears as an intense background in femtosecond time-resolved fluorescence noncollinear optical parametric amplification spectroscopy, which severely interferes the reliable acquisition of the time-resolved fluorescence spectra especially for an optically dilute sample. Superfluorescence originates from the optical amplification of the vacuum quantum noise, which would be inevitably concomitant with the amplified fluorescence photons during the optical parametric amplification process. Here, we report the development of a femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectrometer assisted with a 32-channel lock-in amplifier for efficient rejection of the superfluorescence background. With this spectrometer, the superfluorescence background signal can be significantly reduced to 1/300-1/100 when the seeding fluorescence is modulated. An integrated 32-bundle optical fiber is used as a linear array light receiver connected to 32 photodiodes in one-to-one mode, and the photodiodes are further coupled to a home-built 32-channel synchronous digital lock-in amplifier. As an implementation, time-resolved fluorescence spectra for rhodamine 6G dye in ethanol solution at an optically dilute concentration of 10(-5)M excited at 510 nm with an excitation intensity of 70 nJ/pulse have been successfully recorded, and the detection limit at a pump intensity of 60 μJ/pulse was determined as about 13 photons/pulse. Concentration dependent redshift starting at 30 ps after the excitation in time-resolved fluorescence spectra of this dye has also been observed, which can be attributed to the formation of the excimer at a higher concentration, while the blueshift in the earlier time within 10 ps is attributed to the solvation process.

Fluorescence spectroscopy of Rhodamine 6G: concentration and solvent effects

Rhodamine 6G (R6G), also known as Rhodamine 590, is one of the most frequently used dyes for application in dye lasers and as a fluorescence tracer, e.g., in the area of environmental hydraulics. Knowing the spectroscopic characteristics of the optical emission is key to obtaining high conversion efficiency and measurement accuracy, respectively. In this work, solvent and concentration effects are studied. A series of eight different organic solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, n-pentanol, acetone, and dimethyl sulfoxide (DMSO)) are investigated at constant dye concentration. Relatively small changes of the fluorescence spectrum are observed for the different solvents; the highest fluorescence intensity is observed for methanol and lowest for DMSO. The shortest peak wavelength is found in methanol (568 nm) and the longest in DMSO (579 nm). Concentration effects in aqueous R6G solutions are studied over the full concentration range from the solubility limit to highly dilute states. Changing the dye concentration provides tunability between ∼550 nm in the dilute case and ∼620 nm at high concentration, at which point the fluorescence spectrum indicates the formation of R6G aggregates.

Counting Single Rhodamine 6G Dye Molecules in Organosilicate Nanoparticles

Rhodamine 6G (R6G) dye molecules have been embedded into organosilicate nanoparticles to improve thermal and chemical stability of these marker molecules. We demonstrate that the well-established method of optical single-particle microscopy can be used to determine the number of dye molecules per nanoparticle in such hybrid materials. Analysing the fluorescence intensity of R6G in single nanoparticles, we obtain an average number of 1.3 - 1.7 dye molecules per nanoparticle as compared to 1 R6G per particle obtained from ensemble experiments. The blinking behaviour of embedded R6G can be described by a power law with an exponent α(on/off) = - 1.7. Ensemble measurements complete the optical characterization of the nanoparticles, which reveals no pronounced R6G aggregate formation.

Exploring the role of phase modulation on photoluminescence yield

We report an investigation to elucidate the mechanisms of control in phase-sensitive experiments in two molecular systems. A first inspection of optimization procedures yields the same experimental result: increase in the emission efficiency upon excitation by a phase modulated pulse in a two-photon transition. More detailed studies, which include power dependence, spectral response, one and two color pump-probe and pump-pump experiments show that while for one chromophore phase modulation leads to spectral matching between the two-photon cross section and the second order power spectrum for the other it provides a tool to manipulate the wavepacket dynamics in the excited state.

Fluorescence studies of Rhodamine 6G functionalized silicon oxide nanostructures

Selective anchoring of optically active molecules on nanostructured surfaces is a promising step towards the creation of nanoscale devices with new functionalities. Recently we have demonstrated the electrostatic attachment of charged fluorescent molecules on silicon oxide nanostructures prepared by atomic force microscopy (AFM) nanolithography via local anodic oxidation (LAO) of dodecyl-terminated silicon. In this paper we report on our findings from a more detailed optical investigation of the bound dye Rhodamine 6G. High sensitivity optical wide field microscopy as well as confocal laser microscopy have been used to characterize the Rhodamine fluorescence emission. A highly interesting question concerns the interaction between an emitter close to a silicon surface because mechanisms such as energy transfer and fluorescence quenching will occur which are still not fully understood. Since the oxide thickness can be varied during preparation continuously from 1 to ∼ 5 nm, it is possible to investigate the fluorescence of the bound dye in close proximity to the underlying silicon. Using confocal laser microscopy we were also able to obtain optical spectra from the bound molecules. Together with the results from an analysis of their photochemical bleaching behaviour, we conjecture that some of the Rhodamine 6G molecules on the structure are interacting with the oxide, causing a spectral shift and differences in their photochemical properties.

Guest aggregation within poly(L-lactic acid)/pluronic P104 thin films

Rhodamine 6G (R6G) doped thin films composed of poly(L-lactic acid) (PLLA) and Pluronic P104 were spin cast onto glass microscope slides and characterized by ultraviolet-visible, steady-state, and time-resolved fluorescence spectroscopy. The results show that R6G aggregation within the film increases as the R6G concentration and P104 loading increases. These results suggest an approach for studying drug distributions (monomers, aggregates) within biodegradable polymer formulations.

Emission of Au nanoparticles with and without rhodamine 6G dye

We have observed Stokes and anti-Stokes emission of Au nanoparticles suspended in methanol and rhodamine 6G dye solution. Photoluminescence of Au nanoparticles is a three-step process involving single-photon or three-photon excitation of electron-hole pairs, relaxation of excited electrons and holes, and emission from electron-hole recombination, possibly enhanced by surface plasmons. In the presence of dye, the excitation of anti-Stokes emission of gold involves two-photon absorption in rhodamine 6G molecules followed by the energy transfer to Au nanoparticles with simultaneous absorption of one pumping photon by Au. This mechanism significantly enhances anti-Stokes emission of gold nanoparticles in the presence of dye.

Preparation and surface characterization of polymer nanoparticles designed for incorporation into hybrid materials

We prepared water dispersions of poly(n-butyl methacrylate-st-butyl acrylate) crosslinked core-shell nanoparticles functionalized with different amounts of trimethoxisilane (TMS) groups in the outer shell. The purpose of the TMS groups is to chemically bind the rubbery particles to a nanostructured silica network, using sol-gel copolymerization. Here, we present nanoparticles containing 13 mol % and 30 mol % of TMS groups in the outer shell and compare their surface morphology with particles that do not contain TMS. The particles are prepared by a two-step seeded emulsion polymerization technique at neutral pH. In the first step, we obtained crosslinked seed particles (44 nm in diameter) by a batch process. In the second step, we used a semi-continuous emulsion polymerization technique under starved feed conditions to obtain monodispersed particles of controlled composition and size (ca. 100 nm in diameter). Fluorescence decay measurements were performed in situ on the dispersions, using a pair of cationic dyes adsorbed onto the surface of the nanoparticles: rhodamine 6G as the energy transfer donor and malachite green carbinol hydrochloride as the acceptor. The kinetics of Förster resonance energy transfer (FRET) between the dyes is sensitive to the donor-acceptor distance, allowing us to obtain the binding distribution of the dyes at the nanoparticle surface. For the unmodified nanoparticles, we found a dye distribution that corresponds to an average interface thickness of delta = (5.2 +/- 0.2) nm. For the samples containing 13 mol % and 30 mol % of TMS groups in the outer shell we obtained broader interfaces, with widths of delta = (6.2 +/- 0.2) nm and delta = (6.5 +/- 0.1) nm respectively. This broadening of the distribution with the surface modification is interpreted in terms of the increase in free volume of the shell caused by the TMS groups. Finally, we studied the effect of temperature on the water-polymer interface fuzziness, in order to evaluate the accessibility of the TMS groups during the sol-gel synthesis of nanostructured hybrid materials.