Surface-Enhanced Resonance Raman Scattering: Single-Molecule Detection in a Langmuir–Blodgett Monolayer (original) (raw)
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Adsorption and Surface-Enhanced Raman of Dyes on Silver and Gold Sols'
Several negatively charged dyes were investigated for their possible adsorption on the surface of silver and gold colloidal particles. Those dyes that were found to adsorb on the particles were then checked for surface enhancement of Raman scattering. Highly efficient surface-enhanced Raman scattering (SERS) was observed from a carbocyanine dye in both sols. Excitation-dependence studies as well as adsorption studies confirm the SEW nature of the Raman spectra obtained. The dye is probably aggregated on adsorption and is probably attached through the naphthalene side moiety to the surface. Less efficient SERS was also observed for copper phthalocyanine.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2003
In this paper we report for the first time semi-quantitative analysis of indigo using surface enhanced Raman spectroscopy (SERS) and surface enhance resonance Raman spectroscopy (SERRS). Indigo, a dye widely used today in the textile industry, has been used, historically, both as a dye and as a pigment; the latter in both paintings and in printed material. The molecule is uncharged and largely insoluble in most solvents. The application of SERS/SERRS to the semi-quantitative analysis of indigo has been examined using aggregated citrate-reduced silver colloids with appropriate modifications to experimental protocols to both obtain and maximise SERRS signal intensities. Good linear correlations are observed for the dependence of the intensities of the SERRS band at 1151 cm (1 using laser exciting wavelengths of 514.5 nm (R 0/0.9985) and 632.8 nm (R0/0.9963) on the indigo concentration over the range 10 (7 Á/10 (5 and 10 (8 Á/10 (5 mol dm (3 , respectively. Band intensities were normalised against an internal standard (silver sol band at 243 cm (1). Resonance Raman spectra (RRS) of aqueous solutions of indigo could not be collected because of its low solubility and the presence of strong fluorescence. It was, however, possible to obtain RS and RRS spectra of the solid at each laser excitation wavelength. The limits of detection (L.O.D.) of indigo by SERS and SERRS using 514.5 and 632.8 nm were 9 ppm at both exciting wavelengths. Signal enhancement by SERS and SERRS was highly pH dependent due to the formation of singly protonated and possibly doubly protonated forms of the molecule at acidic pH. The SERS and SERRS data provide evidence to suggest that an excess of monolayer coverage of the dye at the surface of silver colloids is observed at concentrations greater than 7.85)/10 (6 mol dm (3 for each exciting wavelength. The data reported herein also strongly suggest the presence of multiple species of the indigo molecule.
Introduction Photoactive dye molecular assemblies have an important role for the development of functional devices such as solid state dye lasers, chemical sensors and optical storage devices[1]- . Among various techniques of producing organized molecular assemblies, Langmuir-Blodgett (LB) method is one of the most versatile techniques of making well ordered ultrathin films, which are preferred for many applications and permits the control of the twodimensional structure of these films at the molecular level along with ease of multilayer deposition . The advantage of LB films over thin films obtained by using other conventional techniques is that the molecular architecture may be controlled precisely by monitoring certain parameters carefully such as pH of the subphase, barrier speed, dipping speed, molar composition, temperature and surface pressure of deposition of LB film. LB film's immobilizing functional groups have great advantages for the practical applications such as optical biosensor [6] and molecular electronic device . Although amphiphilic dye molecules and many polyaromatic hydrocarbon derivatives have been extensively investigated in terms of spectroscopic properties, comparatively little effort has been made to study water soluble dye molecules assembled in LB films. Recently, a great deal of attention has been devoted to the LB films containing dye molecules owing to their usefulness in the field of sensors and optical devices . Aggregation of some dye molecules into the restricted geometry of LB films have been reported by Bauman [9]-[10]. Recently, we have studied the incorporation of two anionic dyes namely, chicago sky blue and erythrosin B [12] within the Langmuir monolayer and LB films of cationic octadecylamine. Xanthene dyes are one of the most important classes of pigments used in dye lasers and in various photosensitized reactions. For their outstanding photophysical properties, xanthene dyes are very efficient laser dyes . Eosin Y, an important xanthene dye is widely used for the light-induced electron injection from molecular dyes into semiconductor nanoparticles which is the base of numerous technical applications, such as silver photography , xerography [15] and molecular photovoltaics . EY is examined as sensitizers for colloidal CdSnano particles and also as an alternative in the field of dye-sensitized solar cells .Despite such interesting properties, anionic EY films have never been studied in the restricted geometry of LB films. This is the first report on the interaction of EY andDTAB mixed with SA and formcomplex in the Langmuir and Langmuir-Blodgett films. This study was undertaken in order to reveal the adsorption behavior and organization of EY on the complex monolayer film at the air-water interface. Here, SA-DTAB-EY interaction was studied at the air-water interface by measuring Abstract: Interaction ofwater soluble cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) with anionic stearic acid (SA) in presence of a highly fluorescent dye eosin Y (EY) at the air-water interface has been studied. Adsorption kinetics of the complex formation on the water surface shows that, the rate of reaction depends upon DTAB concentration. The stable monolayer formation is mainly occurred due to the electrostatic interaction between SA and DTAB followed by the SA-DTAB-EY complex formation. FTIR study supports this interaction. The resulting complex films are transferred onto quartz substrate at a particular surface pressure to form LB films. UV-Vis absorption and fluorescence spectroscopic studies of complex LB films indicated the interaction of EY dye with DTAB and SA complex and closer association of dye molecules resulting to the formation of aggregates in the LB films. Scanning electron micrograph certainly confirms the formation of aggregates of EY in the complex LB films.
Spectroscopic study of photo-physical parameters of dyes in different solvents environment
Zenodo (CERN European Organization for Nuclear Research), 2023
Surrounding condition has a great role on the spectral characteristics of photosensitive dyes. Solvents having different characteristic and influence in the change of both ground and excited state of photo sensitive dyes as solvent molecules interact with the probe molecule in different way in its microenvironment[1-5]. Photo chemical and photo physical phenomenon are applied in our everyday life like paints, highway hoardings, light fastness in dying fiber and in determining the surfactant characteristics etc. Low energy ground state and high energy exited state electronic transition is the cause of spectroscopic transition. The characteristics of spectroscopic transitions also affected by the free energy changes or interaction among dye and solvents [6-12] molecules. Surface mole fraction of solvents around probe molecules differ from the bulk causes change in spectroscopic properties in mixture of different solvents. Different electronic state arises due to difference of density of electrons [13-18] in surrounding microenvironment of solvent. On the other hand the fluorescence emission spectra of many fluorophores are too much sensitive to the solvent polarity which also responsible for bathochromic spectral shift towards higher wavelength and hypsochromic shifts towards lower wavelength. In general, better stability of dye molecules in the higher energy state due to enhance polar [19]characteristic in compare to the lower energy state andwith increase in solvent polarity indicating lowering the energy of transition through red shift. This work presents solvent effect studies with a number of photo sensitive dyes [11,12] in microenvironment of aprotic and protic medium. From various interaction parameter studies and analysis, it has been found that at exited state dye interact with micro environment either through special intermolecular hydrogen bonding or polarpolar interaction [20-22] with media in case of every dyes.
Journal of Molecular Structure, 2006
Quantitative surface enhanced resonance Raman scattering (SERRS) requires effective adsorption of the analyte onto the metal surface. A range of dyes incorporating the benzotriazole group has been specifically designed to achieve this and they have proved successful labels for obtaining very sensitive analysis. However, if the spectra were more fully understood, the differences between the Raman spectrum in solution and on the surface could provide unique structural information on the nature of the surface layer. Using density functional theory (DFT) calculations the Raman and Infra-red (IR) spectra of the dye 3,5-dimethoxy-4-(6 0 -azobenzotriazolyl)-phenylamine (ABT-DMOPA) were assigned. A good correlation was found between the computed and experimental frequencies. Two competing isomers were compared and gave a largest error in fit for any clearly assigned band in the Raman spectrum of 41 cm K1 and an overall fit error of w15 cm K1 . For the IR spectrum the largest error was 24 cm K1 with an overall fit error of w8 cm K1 .
Molecular and excited state properties of photostable yellow disperse dyes
Journal of Molecular Structure, 2020
Synthetic dyes having high photostability on hydrophobic fibers such as poly(ethylene terephthalate) (PET) are of interest for use on textile substrates for outdoor applications. While much is known about photostable dyes developed for PET in the 1980s, owing to their viability for use in automobile interiors, little has been published on currently viable photostable disperse dyes. As part of an effort to help fill this void and to facilitate future photostable disperse dye design, the present study involved the use of experimental measurements and modelling studies to help characterize the molecular structures of commercially viable dyes for producing photostable colors on PET fibers, beginning with a pair of blue dyes. With the aid of HR-MS, 500 MHz 1 H NMR, and X-ray crystallography, it was established that the two dyes are structural isomers having 1,5-(OH) 2-anthraquinone (AQ) and 1,8-(OH) 2-AQ base structures. It is proposed that the photostability of these dyes arises from the presence of multiple OH/NH groups ortho to the AQ C]O groups which enables them to dissipate excited state energy through intramolecular proton transfer. Further, using DFT-based molecular modelling studies, it was shown that the dye having the 1,5-(OH) 2-AQ base structure has a lower ESOP than the isomeric dye having the 1,8-(OH) 2-AQ base structure. Similarly, results from calculating Frontier HOMO and LUMO isosurfaces indicated that the LUMO lobes of the latter dye are larger, suggesting that this dye undergoes excitation faster than the 1,5-(OH) 2-AQ isomer.