State Fluorescence Techniques Research Articles

Experimental and Quantum Chemical Calculations of Imidazolium Appended Naphthalene Hybrid in Different Biomimicking Aqueous Interfaces.

The effect of solvent polarity and micellar headgroup on a newly designed imidazolium based ionic liquid (IL) conjugated with naphthalene, 1,2-dimethyl-3-((6-(octyloxy)naphthalen-2-yl)methyl)-1H-imidazol-3-ium chloride (IN-O8-Cl), was studied using steady state and time-resolved fluorescence techniques. We observed that the dipole moment in the excited state is remarkably higher than the ground state. The effect of micellar surface charge on the photophysics of IN-O8-Cl in aqueous phase at room temperature was investigated. Formation of premicellar aggregates in sodium dodecylsulfate (SDS) was perceived; further the microenvironment of IN-O8-Cl was examined using steady-state fluorescence spectroscopy. Micropolarity of the micellar environment of SDS was found to be lower than that of cetyltrimethylammonium bromide (CTAB) and triton X-100 (TX100) following the order SDS < TX-100 < CTAB. The binding constant (Kb) and edge excitation red shift (EERS) from the emission maximum suggest that the probe binds strongly to the micelles. Multiexponential behavior was observed in time-resolved fluorescence lifetime studies in all micellar environments. We have observed an increase in rotational correlation time as we move from pure aqueous phase to solution containing surfactants of different head charge. Varieties of spectral parameters were used to justify the region in which the probe is present. The experimentally obtained dipole moment data were justified and explained by the DFT calculations of the electronic properties of IN-O8-Cl molecules in gas phase and in selected solvents.

Photoinduced electron transfer from silyl end-capped sexithiophene to benzoquinone derivatives studied by laser photolysis

Abstract Photoinduced electron transfer from the electron-donating bis(dimethyl- n -octylsilyl)sexithiophene, (DSi6T), to the electron-accepting benzoquinone derivatives, BQs, in polar benzonitrile has been investigated with laser photolysis method. The employed benzoquinone derivatives include 1,4-benzoquinone (BQ), 2,5-dichloro-1,4-benzoquinone (Cl 2 BQ), 2,6-dimethyl-1,4-benzoquinone (Me 2 BQ), tetrafluoro-1,4-benzoquinone (F 4 BQ) and 2-methyl-1,4-benzoquinone (MeBQ). The electrochemical measurements showed pronounced effect of the substituted groups on the reduction potentials of BQs, and consequently on the driving forces of the electron transfer of the DSi6T/BQs mixture systems. Such effect of the driving forces for electron-transfer reactions of DSi6T/BQs mixture systems have been examined by utilizing the femtosecond and nanosecond laser flash photolysis, in addition the complementary steady state absorption and fluorescence techniques. Upon excitation of DSi6T with 440 nm laser light, the electron-transfer reactions from the triplet excited state of DSi6T to BQs were confirmed by observing the transient absorption bands of DSi6T radical cation in the visible region. The excellent electron donating properties of DSi6T suggests its potential to be a photoactive unit in the bulk heterojunction solar cells.

Fluorescence study of effect of particle size in PS latex/Al2O3 nanocomposite films

Steady state fluorescence and BioUV-Visible techniques were used to study film formation of polystyrene (PS) latex and Al2O3 composites depending on PS particles size and Al2O3 content. Two film series (SmPS/Al2O3 and LgPS/Al2O3) were prepared covering PS sphere (SmPS: 203 nm; LgPS: 382 nm) templates with various layers of Al2O3 by dip coating method. The film formation behaviours of composites were studied by annealing them at a temperature range of 100–250°C and monitoring the scattered (Isc), fluorescence (IP) and transmitted (Itr) light intensities after each annealing step. The results indicate that LgPS/Al2O3 films underwent complete film formation independent of Al2O3 content while no film formation occurred above a certain Al2O3 content for SmPS/Al2O3. Extraction of PS produced ordered porous structures for high Al2O3 content in both series. Scanning electron microscopy images showed that the pore size and porosity could be easily tailored by varying PS particle size and Al2O3 content.

Application of Fluorescence Techniques to Characterise the Preparation of Protein-Containing Sol-Gel Derived Hosts for use as Catalytic Media

In this work we collate and review the usage that we have made of fluorescence techniques employed to follow the sol to gel transition and aging in different tetraethylorthosilicate based materials. The sol-gel method allows porous glasslike of good optical quality to be produced at relatively low (ambient) temperatures, which facilitates the incorporation of a range of molecules; from laser dyes to biomolecules. Here the use of “common” viscosity (DASPMI) and polarity (Nile red) sensitive fluorescence probes to monitor the host manufacture is made. Nile red was also used to label two catalytically active proteins (cytochrome c and subtilisin Carlsberg). These were incorporated into the different host media and the dye used to ascertain changes in protein conformation, both upon incorporation and at the end of an aging period. Complementary measurements of catalytic activity were performed. The probe emission was monitored via steady state and time-resolved fluorescence techniques and comparison made with the catalytic activity measurements to elucidate the amount of accessible and active protein. Overall it was found that the hosts became stable after an aging period approaching 20 days and that the major influence on the catalytic reaction rates was that of host mediated mass transport.

SORPTION AND SLOW RELEASE KINETICS OF PAAM GELS AT VARIOUS TEMPERATURES

Small molecule sorption and slow release in and out of polyacrylamide (PAAm) gels were studied by using steady state fluorescence (SSF) technique. Pyranine (Py) dissolved in water used as a probe. Fluorescence emission intensity, I p from Py was used to monitor for studying sorption and slow release processes at various temperatures. Sorption and slow release processes were analyzed by using Fickian diffusion model and coefficients were obtained. Related activation energies were also calculated for the corresponding physical processes.

Universality of sol--gel phase transition of κ-carrageenan in various salts: a steady state fluorescence study

Thermal phase transitions of κ-carrageenan in NaCl, KCl and CaCl2 solutions were studied using steady state fluorescence (SSF) technique. Pyranine was introduced as a fluorescence probe for studying sol--gel phase transitions. Scattered light, I sc and fluorescence intensity, I was monitored against temperature to determine the sol--gel (T sg) phase transition temperatures. It was observed that T sg values are strongly correlated to NaCl, KCl and CaCl2 contents. The weight average degree of polymerization, DP w and gel fraction G, exponents (γ and β) were measured and found to be in accord with the classical Flory--Stockmayer model, i.e., γ and β were found to be close to 1.0, independent of salt content.

Film formation from TiO2-polystyrene latex composite: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique for studying film formation from TiO2 covered polystyrene (PS) latex particles. The composite films were prepared from pyrene (P)-labeled PS particles by covering them with TiO2 at room temperature and then annealed at elevated temperatures in 10 min time interval above glass transition (T g) temperature of polystyrene. Five different composite films were studied in various TiO2 layer contents. Fluorescence intensities I P from P were measured after each annealing step to monitor the stages of film formation. Films showed considerable increase in I P above the certain onset temperature called minimum film forming temperature, T 0. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 23.12 and 92.80 kJ mol−1, respectively.

Study on critical behaviour in N -isopropyl acrylamide gels by using fluorescence technique

The steady state fluorescence (SSF) technique was used to study the sol-gel transition for the solution free radical crosslinking copolymerization of N-isopropyl acrylamide (NIPA), with N,N′-methylenebis (acrylamide) (BIS) as crosslinker in the presence of ammonium persulfate (APS) as an initiator. Pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid, trisodium salt, HPTS) was used as a floroprobe for monitoring the polymerization. Pyranine molecules start to bind to NIPA polymer chains upon the initiation of the polymerization, thus the spectra of the bonded pyranines shift to the shorter wavelengths. The gel fraction exponent β and the weight average degree of polymerization exponent γ′ agree best with the mean-field (Flory-Stockmayer) results near the gel point for various crosslinker contents.

Universal Behaviour of Gel Formation from Acrylamide-Carrageenan Mixture Around the Gel Point: A Fluorescence Study

The steady state fluorescence (SSF) technique was used to study the sol-gel transition, for the solution free radical crosslinking copolymerization of acrylamide (AAm) with various carrageenan content. N, N′- methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) are used as crosslinker and an initiator, respectively. Pyranine (8-hydroxypyrene-1, 3,6-trisulfonic acid, trisodium salt, HPTS) was added as a floroprobe for monitoring the polymerization. Pyranine molecules start to bind to acrylamide polymer chains upon the initiation of the polymerization; thus, the spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allows one to monitor the sol-gel transition, without disturbing the system mechanically, and to test the universality of the sol-gel transition as a function of some kinetic parameters like polymer concentration. Observations around the critical point show that the gel fraction exponent β obeyed the percolation result for low carrageenan concentrations (<2.0%) however classical results were produced at higher carrageenan concentration (>2.0%).

Dissolution of Al2O3-polystyrene latex composites: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique to study dissolution of a composite film formed from a mixture of Al2O3 and polystyrene (PS) latex particles. The composite films were cast from dispersion of pyrene (P)-labeled PS particles in Al2O3 solution at room temperature and annealed at 280°C temperature for 10 min. Eight different composite films were studied in various latex contents. Toluene was used as dissolution agent. Fluorescence intensities I P from P were monitored during dissolution. Fickian diffusion was employed to model the dissolution processes. Dissolution coefficients, D d, were measured and found to be increased at high PS content in the composite films.

Photoinduced electron transfer from chloropromazine and promethazine to chloroalkanes accompanied by cleavage of C–Cl bond

Electron transfer from two phenothiazine derivatives namely promethazine and chloropromazine to chloroalkanes namely carbontetrachloride and chloroform has been studied by steady state fluorescence and transient absorption techniques. These phenothiazine derivatives also form weak charge transfer complexes with the above two chloroalkanes. Picosecond transient absorption studies provide direct evidence for two processes: (1) charge separation in the charge transfer complex and (2) electron transfer from the excited state of phenothiazines to chloroalkanes. A modified Marcus electron transfer theory proposed by Saveant [J. Am. Chem. Soc. 109 (1987) 6788], which incorporates the bond cleavage, has been used to explain the observed experimental results.

Void closure by viscous flow during coalescence of hard latex particles

Steady state fluorescence (SSF) technique was used to study the void closure process during coalescence of hard latex particles. Latex films were prepared by annealing pyrene (Py)-labelled poly(methyl methacrylate) particles above the glass transition temperature. During the annealing processes, the optical clarity of the film increased considerably. Direct fluorescence emission from excited pyrene was monitored as a function of annealing temperature to detect these changes. Scanning electron microscopy in conjunction with Monte Carlo simulations of photon diffusion in latex film were used to interpret the fluorescence results. Void Closure temperature (Tc) and time (tc) were measured at the point at which the fluorescence emission intensity becomes maximum. This was associated with the longest optical path of a photon in latex film. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 651–659, 1997

Fluorescence Technique for Studying the Sol--Gel Transition in the Free--Radical Crosslinking Copolymerization of Methyl Methacrylate and Ethylene Glycol Dimethacrylate

The steady--state fluorescence technique was used to study the free--radical crosslinking copolymerization [1] of methyl meth\-acryl\-ate and ethyl\-ene glycol di\-meth\-acryl\-ate in the absence and presence of toluene at 74^\circC. A sol--gel phase transition was observed and monitored by an excited aromatic molecule during the gelation of the above system. Bond percolation theory was employed to qualify the results [2,3]. The critical exponent and gel point were found to be 0.45 and 0.36 both in bulk and solution polymerization [4].