Inner filter effect and the onset of concentration dependent red shift of synchronous fluorescence spectra

The phenomenon of concentration dependent red shift, often observed in synchronous fluorescence spectra (SFS) of monofluorophoric as well as multifluorophoric systems at high chromophore concentrations, is known to have good analytical advantages. This was previously understood in terms of large inner filter effect (IFE) through the introduction of a derived absorption spectral profile that closely corresponds to the SFS profile. Using representative monofluorophoric and multifluorophoric systems, it is now explained how the SF spectral maximum changes with concentration of the fluorophore. For dilute solutions of monofluorophores the maximum is unchanged as expected. It is shown here that the onset of red shift of SFS maximum of both the mono as well as the multifluorophoric systems must occur at the derived absorption spectral parameter value of 0.32 that corresponds to the absorbance value of 0.87. This value is unique irrespective of the nature of the fluorophore under study. For monofluorophoric systems, the wavelength of derived absorption spectral maximum and the wavelength of synchronous fluorescence spectral maximum closely correspond with each other in the entire concentration range. In contrast, for multifluorophoric systems like diesel and aqueous humic acid, large deviations were noted that could be explained as to be due to the presence of non-fluorescing chromophores in the system. This work bridges the entire fluorophore concentration range over which the red shift of SFS maximum sets in; and in the process it establishes the importance of the derived absorption spectral parameter in understanding the phenomenon of concentration dependent red shift of SFS maximum.     

Charge-localized naphthalene-bridged bis-hydrazine radical cations

Electron transfer (ET) in four symmetrically substituted naphthalene-bridged bis-hydrazine radical cations (1,4; 1,5; 2,6; and 2,7) is compared within the Marcus-Hush framework. The ET rate constants (k(ET)) for three of the compounds were measured by ESR; the 2,7-substituted compound has an intramolecular ET that is too slow to measure by this method. The k(ET) values are significantly dependent upon the substitution pattern of the hydrazine units on the naphthalene bridge but do not correlate with the distance between them. This is contrary to an assumption that is frequently made about intervalence compounds that the bridge serves only as a spacer that fixes the distance between the charge-bearing units. The internal vibrational and solvent portions (lambda(v) and lambda(s)) of the total reorganization energy (lambda) have been separated using solvent effects on the intervalence band maximum, resulting in a lambda(v) that is the same, 9900 cm(-1), for the differently substituted naphthalenes. This is in accord with the general assumption that lambda(v) is primarily dependent upon the charge bearing unit and not the bridge. However, the trends in lambda(s) cannot be explained by dielectric continuum theory.     

Electrogenerated chemiluminescence of a spirobifluorene-linked bisanthracene: a possible simultaneous, two-electron transfer

We report the electrogenerated chemiluminescence (ECL) of 2,2'-bis(10-phenylanthracen-9-yl)-9,9'-spirobifluorene (spiro-FPA), a dichromophoric molecule composed of two phenylanthracenes linked by a spirobifluorene moiety (PA-X-PA). The results are compared to those for 9,10-diphenylanthracene (DPA), a related molecule with a single chromophore. Cyclic voltammetry (CV) of spiro-FPA shows two reversible, closely spaced, one-electron transfers on both reduction and oxidation, occurring at E(o)(1,red) = -2.02, E(o)(2,red) = -2.07 V vs SCE and E(o)(1,ox) = 1.14, E(o)(2,ox) = 1.20 V vs SCE. The potentials for each pair are close enough to appear as a single peak in CV, indicating that the spirobifluorene moiety interrupts conjugation between the redox centers. The potentials observed are similar to those of DPA, which shows E(o)(red) = -2.06 V vs SCE and E(o)(ox) = 1.15 V vs SCE. The absorbance spectrum of spiro-FPA shows lambda(max,abs) = 377 nm, with 377 = 25,700 M(-1) s(-1), while DPA exhibited lambda(max,abs) = 374 nm, with 374 = 13,800 M(-1) s(-1), demonstrating that spiro-FPA has twice the available chromophores as DPA. Photoluminescence (PL) data for spiro-FPA shows lambda(max,PL) = 434 nm, with Phi(PL) = 0.74, while DPA fluoresces at 420 nm with Phi(PL) = 0.91; thus, there is greater solvent or structural relaxation in the spiro-FPA excited state, which may account for the greater internal conversion. Unlike DPA, the ECL spectrum of spiro-FPA exhibits long-wavelength emission not observed in the PL. We attribute this emission to excimers formed during annihilation ECL. Steric hindrance prevents DPA from forming excimers, even in ECL, but spiro-FPA annihilation can occur between pairs of di-ions (PA(*-)-X-PA(*-) and PA(*+)-X-PA(*+)), which are electrostatically more strongly attracted to one another than the mono-ions. This greater electrostatic attraction may be sufficient to overcome the steric hindrance to excimer formation. Lowering the electrolyte concentration decreases the electrostatic shielding of the ions from one another; thus, the increase in longer wavelength ECL accompanying a decrease in electrolyte concentration supports the role of the di-ions in excimer formation. Additionally, simulations show, consistent with experiment, a more rapid decrease in excimer concentration than in excited monomer concentration as a function of time after each potential pulse. This is probably due to the greater number of scavenging reactions available for di-ions. The simulations are confirmed experimentally when lower potential pulsing frequencies yield lower relative excimer emission. Since an excited state created by one-electron transfer between two di-ions should be rapidly quenched via electron transfer by the other PA moiety, the existence of excimers suggests the possibility of simultaneous, two-electron transfer to generate the excimer.     

Intermolecular energy transfer involving an iridium complex studied by a combinatorial method

A recently developed combinatorial method utilizing angular dependence of evaporation rate was used to create compositional spread thin film libraries of Tris(2-pyridin-2-yl-indolizino[3,4,5-ab] isoindole-C(1), N('))iridium(III) [Ir(pin)(3)] and 4,4(')-N,N(')-dicarbazol-biphenyl (CBP) composite, with the molar fraction of Ir(pin)(3) complex varying in the 0.0003Ir(pin)(3) energy transfer proceeds by the Forster mechanism with the Forster radius of 30 A. The CBPxIr(pin)(3) composite has the highest photoluminescence quantum efficiency approximately 0.95, for chi(Ir(pin)(3) )=0.03 and is characterized by a structured green emission (lambda(max)=538 nm) originating from the ligand-centered (pi-pi(*))(3) state of the Ir(pin)(3) complex. On the contrary, the PL spectra of Ir(pin)(3) bulk are characterized by a weak red emission (lambda(max)=673 nm) attributed to the lowest metal-to-ligand charge transfer state. A statistical analysis based on a binomial distribution indicates that the emission from the (pi-pi(*))(3) state is quenched in Ir(pin)(3) molecules that are in a direct contact with each other.     

Solvent and concentration effects on the visible spectra of tri-para-dialkylamino-substituted triarylmethane dyes in liquid solutions

We have characterized the spectroscopy properties of crystal violet (CV+) and ethyl violet (EV+) in liquid solutions as a function of the solvent type and dye concentration. The analysis of how solvent properties and dye concentration affects the electronic spectra of these tri-para-dialkylamino substituted tryarylmethane (TAM+) dyes was performed on the basis of two spectroscopic parameters, namely the difference in wavenumber (deltanu) between the maximum and the shoulder that appears in the short-wavelength side of the respective maximum visible band (deltanu = 1/lambda(shoulder)-1/lambda(max) cm(-1)), and the wavelength of the maximum absorption (lambda(max)). The solvent and the concentration effects on lambda(max) and deltanu have indicated that both solute/solute (ion-pairing and dye aggregation) and solute/solvent (H-bonding type) interactions modulate the shape of the visible electronic spectra of these dyes in solution. In solvent with small dieletric constant (epsilon < approximately 10), the formation of ion-pairs represents a major contribution to the shaping of these spectra. Upon increasing dye concentration the formation of ion-pairs was characterized by an increase in deltanu observed concomitantly with a red shift in lambda(max) In chloroform and chlorobenzene the ion-pair association constant of CV+ and EV+ with Cl- ions were found to be in the order of 10(6) and 10(5) M(-1), respectively. In trichloroethylene the association constant for the CV+Cl- pair was 10(8) M(-1). In water, dye aggregation instead of ion-pairing represents a major contribution to the shaping of the visible spectra of CV+ and EV+. Dye aggregation was indicated by an increase in deltanu observed concomitantly with a blue shift in lambda(max) upon increasing dye concentration. The distinct behavior of deltanu for dye aggregation and ion-pairing as a function of dye concentration can therefore assist in the characterization of these two distinct phenomena. The solute/solvent interactions were studied in a series of polar solvents in which solute/solute interactions do not occur in any detectable extent. The dependence found for deltanu as a function of the Kamlet-Tafts solvatochromic parameters (alpha, beta and pi*) is in keeping with previous inferences indicating that the splitting in the overlapped absorption band of CV+ and EV+ in hydroxilated solvents arises from a perturbation in the molecular symmetry induced by hydrogen bonding (donor-acceptor) type interactions with solvent molecules. A distinction between the effects of solute/solute and solute/solvent interactions on the visible spectra of these dyes is provided.     

Synthesis and self-association, absorption, and fluorescence properties of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes

The dual Sonogashira coupling reactions of 1,3,5-tribromo-2,4,6-triiodobenzene with p-X-phenylacetylene followed by another p-Y-phenylacetylene (X, Y = OSiMe(2)Bu-t or CO(2)Et) produced a series of differentially functionalized hexakis(p-substituted-phenylethynyl)benzenes with D(3)(h)() symmetry (3h: 1,3,5-X-2,4,6-Y) and C(2)(v)() symmetry (3g,i: 1,2,3,5-X-4,6-Y; 3f,j: 1-X-2,3,4,5,6-Y). In a similar manner, 1,3,5-tris(p-X-phenylethynyl)-2,4,6-tris(p-Y-phenylethynyl)benzenes and 1,2,3,5-tetrakis(p-X-phenylethynyl)-4,6-bis(p-Y-phenylethynyl)benzenes (3l: X = OSiMe(2)Bu-t, Y = NO(2); 3m,n: X = N(n-octyl)(2), Y = NO(2); 3o,p: X = N(n-octyl)(2), Y = CH(OCH(2)CH(2)O); 3q,r: X = N(n-octyl)(2), Y = CHO; 3s,t: X = N(n-octyl)(2), Y = CH=C(CN)(2)) were prepared. Compounds 3 with electron-withdrawing groups self-aggregated by a pi-pi stacking interaction and solvophobic effect. In the absorption and fluorescence spectra of 3, lambda(max)(abs) and lambda(max)(em) showed red shifts as the donor-acceptor dipole at the end functional groups of the para position was increased. In the absorption spectra, lambda(max)(abs) showed red shifts upon increasing the number of combination of electron-donating and -withdrawing groups on the diagonal line in a molecule, whereas lambda(max)(em) in the fluorescence spectra exhibited red shifts upon decreasing the molecular symmetry.     

An experimental and theoretical investigation of the photophysics of 1-hydroxy-2-naphthoic acid

Photophysical and photochemical properties of 1-hydroxy-2-naphthoic acid (1,2-HNA) have been investigated experimentally by steady state and time domain fluorescence measurements and theoretically by Hartree-Fock (HF), configuration interaction at the single excitation (CIS) level, density functional theoretic (DFT), and semiempirical (AM1) methods. 1,2-HNA exhibits normal fluorescence that depends on its concentration, nature of the solvent, pH, temperature, and wavelength of excitation. It seems to form different emitting species in different media, akin to 3-hydroxy-2-naphthoic acid (3,2-HNA). The large Stokes shifted emission observed at pH 13 is attributed to species undergoing excited-state intramolecular proton transfer. Nonradiative transition seems to increase on protonation and decrease on deprotonation. AM1(PECI=8) calculations predict the absorption maximum (lambda(max) = 335.9 nm) in reasonable agreement with experiment (lambda(max) = 352 nm) for the neutral 1,2-HNA. They also predict a red shift in absorption on protonation and a blue shift on deprotonation as observed experimentally. CIS calculations tend to overestimate the energy gap and hence underestimate the absorption maxima between the ground and the excited electronic states of 1,2-HNA and its protonated and deprotonated forms. However, they do predict correctly that the excited state intramolecular proton transfer is likely to occur in the deprotonated form of 1,2-HNA and not in the neutral and the protonated forms. A single minimum is found in the potential energy profile for the ground state as well as the first excited state of 1,2-HNA and its protonated species. In contrast, a double minimum with a nominal barrier in between is predicted for the ground state and also the first three excited states of the deprotonated species. The keto form of the deprotonated species is found to be slightly less stable than the enol form in all the states investigated.     

Solvent effect on the optical property of uranyl acetylacetonate monohydrate

The lability of the [UO2(acac)2H2O] complex has been exploited to decipher solvent composition of a medium. Successive blue shift of the π-π* band (λmax=282 nm) is observed due to alcohol substitution of increasing chain length in place of water. This observation helps to quantify the chain lengths of normal alcohol. The result has been accounted theoretically. However, in non-coordinating solvent, irregular red shift of the π-π* band is observed because of the molecular complexity. Again, charge transfer (CT) band at 211 nm has been identified employing polar-polar and polar coordinating-non-coordinating solvent systems.     

Enhancement of metal-metal coupling at a considerable distance by using 4-pyridinealdazine as a bridging ligand in polynuclear complexes of rhenium and ruthenium

Novel polynuclear complexes of rhenium and ruthenium containing PCA (PCA = 4-pyridinecarboxaldehyde azine or 4-pyridinealdazine or 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene) as a bridging ligand have been synthesized as PF(6-) salts and characterized by spectroscopic, electrochemical, and photophysical techniques. The precursor mononuclear complex, of formula [Re(Me(2)bpy)(CO)(3)(PCA)](+) (Me(2)bpy = 4,4'-dimethyl-2,2'-bipyridine), does not emit at room temperature in CH(3)CN, and the transient spectrum found by flash photolysis at lambda(exc) = 355 nm can be assigned to a MLCT (metal-to-ligand charge transfer) excited state [(Me(2)bpy)(CO)(3)Re(II)(PCA(-))](+), with lambda(max) = 460 nm and tau < 10 ns. The spectral properties of the related complexes [[Re(Me(2)bpy)(CO)(3)}(2)(PCA)](2+), [Re(CO)(3)(PCA)(2)Cl], and [Re(CO)(3)Cl](3)(PCA)(4) confirm the existence of this low-energy MLCT state. The dinuclear complex, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(II)(NH(3))(5)](3+), presents an intense absorption in the visible spectrum that can be assigned to a MLCT d(pi)(Ru) --> pi(PCA); in CH(3)CN, the value of lambda (max) = 560 nm is intermediate between those determined for [Ru(NH(3))(5)(PCA)](2+) (lambda(max) = 536 nm) and [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](4+) (lambda(max) = 574 nm), indicating a significant decrease in the energy of the pi-orbital of PCA. The mixed-valent species, of formula [(Me(2)bpy)(CO)(3)Re(I)(PCA)Ru(III)(NH(3))(5)](4+), was obtained in CH(3)CN solution, by bromine oxidation or by controlled-potential electrolysis at 0.8 V in a OTTLE cell of the [Re(I),Ru(II)] precursor; the band at lambda(max) = 560 nm disappears completely, and a new band appears at lambda(max) = 483 nm, assignable to a MMCT band (metal-to-metal charge transfer) Re(I) --> Ru(III). By using the Marcus-Hush formalism, both the electronic coupling (H(AB)) and the reorganization energy (lambda) for the metal-to-metal intramolecular electron transfer have been calculated. Despite the considerable distance between both metal centers (approximately 15.0 Angstroms), there is a moderate coupling that, together with the comproportionation constant of the mixed-valent species [(NH(3))(5)Ru(PCA)Ru(NH(3))(5)](5+) (K(c) approximately 10(2), in CH(3)CN), puts into evidence an unusual enhancement of the metal-metal coupling in the bridged PCA complexes. This effect can be accounted for by the large extent of "metal-ligand interface", as shown by DFT calculations on free PCA. Moreover, lambda is lower than the driving force -DeltaG degrees for the recombination charge reaction [Re(II),Ru(II)] --> [Re(I),Ru(III)] that follows light excitation of the mixed-valent species. It is then predicted that this reverse reaction falls in the Marcus inverted region, making the heterodinuclear [Re(I),Ru(III)] complex a promising model for controlling the efficiency of charge-separation processes.     

TD-DFT investigation of the UV spectra of pyranone derivatives

The UV absorption spectra of more than 80 substituted coumarins and chromones have been investigated with the PCM-TD-DFT theoretical scheme using three hybrid functionals (O3LYP, B3LYP, and PBE0) and taking into account methanol or ethanol solvation effects. For most of the studied derivatives, there are at least two allowed excited states presenting a strong oscillator strength in the UV region. The first allowed excitation is associated to a HOMO-LUMO transition whereas the second corresponds to a transition from the HOMO-1 to the LUMO. Both involve a charge transfer from the benzenic cycle to the pyranone moiety. Statistically treating the PBE0 results allows a prediction of the lambda(max) with small standard deviations: in methanol, 6 nm (0.07 eV) for the first excitation (lambda(max)(1)) and 5 nm (0.08 eV) for the second one (lambda(max)(2)), whereas in ethanol 6 nm (0.08 eV) for (lambda(max)(1)) and 6 nm (0.13 eV) for (lambda(max)(2)).     

Alkyl halide charge transfer complexes with hard Lewis bases

The unusual charge transfer complexes formed between alkyl halide acceptors and hard Lewis base donors (amines and alcohols) in low dielectric solvent were examined using ultraviolet spectroscopy. The lambda(max) of the complex decreases with increasing ionization potential of the donor. The complex formation equilibria were probed by thermodynamic analysis and concentration variation. At ambient temperatures complex formation is generally slightly exergonic with a negative complexation entropy. The complex extinction coefficients are much lower (<10 l mol(-1) cm(-1)) than for typical charge transfer complexes. These complexes are extraordinary within a classical context since the halide acceptors have a negative electron affinity. They exhibited an atypical hypsochromic shift with increasing solvent dielectric constant.     

Stability analysis of environmentally benign green emulsion liquid membrane

A new stable green emulsion liquid membrane (GELM) was formulated by selecting the environmentally benign vegetable oils. The rice bran oil (RBO) based GELM has shown better stability in comparison to that obtained from other oils. GELM was prepared using 10?mL RBO, 0.25 [M] NaOH concentration, 2 (v/v, %) surfactant concentration, 0.4 (v/v) phase ratio, 2000?rpm emulsification speed, and 20?min emulsification time. Under these optimum conditions, GELM has been found to be stable for 120?±?2?min (no significant phase change) and has shown complete phase separation after 4 hours. Therefore, RBO as a green solvent has high potential to be applied in several ELM process applications.     

Effect of protein relaxation on electron transfer from the cytochrome subunit to the bacteriochlorophyll dimer in Rps. sulfoviridis reaction centers within mixed adiabatic/nonadiabatic model

The broad set of nonexponential electron transfer (ET) kinetics in reaction centers (RC) from Rhodopseudomonas sulfoviridis in temperature range 297-40 K are described within a mixed adiabatic/nonadiabatic model. The key point of the model is the combination of Sumi-Marcus and Rips-Jortner approaches which can be represented by the separate contributions of temperature-independent vibrational (v) and temperature-dependent diffusive (d) coordinates to the preexponential factor, to the free energy of reaction DeltaG=DeltaG(v)+DeltaG(d)(T) and to the reorganization energy lambda=lambda(v)+lambda(d)(T). The broad distribution of protein dielectric relaxation times along the diffusive coordinate is considered within the Davidson-Cole formalism.     

Spectroscopic studies of a near-infrared absorbing pH sensitive aminodienone-carbocyanine dye system

Synthetic red and near-infrared absorbing dyes may be used as probe molecules in a large number of applications. Dyes exhibiting spectral changes with hydrogen ion concentration are useful as pH probes. Those dyes which have their absorption and fluorescence maxima in the long wavelength region of the visible spectral region are specially valuable because of decreased interference and semiconductor laser applications. In this paper we have evaluated an aminodienone dyes 1 which demostrates pH dependent absorption and fluorescence spectra as well as solvent polarity dependence. In organic solvents the long wavelength absorption band of the dye is in the reduced interference region. The absorption maximum is at 535 nm in neutral or alkaline solutions in methanol. The absorption spectra undergo a strong bathochromic shift in the presence of acids (lambda(max) = 709 nm) with a concomitant change in the fluorescence spectra. This pH sensitive dye was found to be specially especially useful for organic solvents. The analytical utility of this and similar near-infrared absorbing dyes is discussed.     

Steric guided change of electron transfer mechanism in benzene

In fluorescence quenching study via electron transfer (ET), the quenching rate constant (k(q)) values generally decrease with lowering of quencher concentration, since smaller concentration of quencher always leads to a red shift in the donor-acceptor (D-A) distance in ET [M. Tachiya, S. Murata, J. Phys. Chem. 96 (1992) 8441; S. Murata, M. Tachiya, J. Phys. Chem. 100 (1996) 4064; L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A 103 (1999) 5882]. However, while doing a comparative study with different carbazole (CZ) derivatives-1,4-dicyanobenzene (DCB) systems in benzene (BZ), we observed a deviation from that normal behaviour. It was found that for all of them with lower quencher (DCB) concentration, k(q) values actually increase instead of the expected reduction. Exceptionally, for simple CZ (C12H9N) with decrease in concentration of DCB, k(q) values can even reach the order of energy transfer (10(11) s(-1)). Interestingly, it is not observed when toluene (TL) or xylene (XY) is used as solvent. To explain this unique observation, a sandwich type of molecular structure is predicted, where BZ sliding in between CZ and DCB brings them closer enough, imparting more through bond character to CZ-DCB interaction and hence a higher rate of ET (k(q)) is observed [L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A. 103 (1999) 5882].     

Photochemistry of a chiral salen aluminum complex in nonconventional solvents: use of imidazolium ionic liquids and chiral alcohols

The photochemistry of a chiral (salen)aluminum(III) chloride complex has been studied in nonconventional solvents, namely, two imidazolium ionic liquids differing on the hydrophobicity (hydrophilic BF(4)(-) or hydrophobic PF(6)(-) counter anions) and in chiral 2-butanols (R and S). Upon 355 nm laser excitation, the same transient absorption spectrum (with some solvatochromic shift in lambda(max)) was recorded in all cases and assigned to the (salen)Al(II) complex with radicaloid character at the metal atom. This intermediate arises from the photoinduced homolytic cleavage of the apical Al-Cl bond. The half-life of this radicaloid Al(II) species varies depending on the solvent, indicating that its reactivity is governed by the nature of the ionic liquid and also on the R or S configuration of the chiral alcohol.     

Edge excitation red shift and energy migration in quinine bisulphate dication

Photoinduced excited state dynamical processes in quinine sulphate dication (QSD) have been studied over a wide range of solute concentrations using steady state and nanosecond time-resolved fluorescence spectroscopic techniques. The edge excitation red shift (EERS) of emission maximum, emission wavelength dependence of fluorescence lifetimes and the time dependence of emission maximum are known to occur due to the solvent relaxation process. With increase in solute concentration, the emission spectrum shifts towards the lower frequencies accompanied with decrease in fluorescence intensity, however, absorption spectrum remains unchanged. A decrease in EERS, fluorescence lifetimes, time dependent fluorescence Stokes shift (TDFSS), fluorescence polarization and the solvent relaxation time (τ_r) is observed with the increase in solute concentration. The process of energy migration among the QSD ions along with solvent relaxation has been found responsible for the above experimental findings.     

Determination of ruthenium and osmium in each other's presence in chloride solutions by direct and third-order derivative spectrophotometry

Ruthenium and osmium (up to 20 mug Ru(Os) ml(-1)) can be determined in chloride solutions directly after absorption of RuO(4) and OsO(4) in hydrochloric acid. In 9 M HCl, RuO(4) and OsO(4) are quantitatively converted into RuCl(6)(2-) (lambda(max) = 480.0 nm, epsilon = 4.8 x 10(3) l mol(-1) cm(-1)) and OsCl(6)(2-) (lambda(max) = 334.8 nm, epsilon = 8.4 x 10(3) l mol(-1) cm(-1)) respectively. Osmium does not interfere with the determination of ruthenium in the form of the RuCl(6)(2-) complex by direct spectrophotometry. The absorbance of the obtained solution at lambda(max) = 480.0 nm corresponds only to the concentration of ruthenium. A derivative spectrophotometric method using numerical calculation of absorption spectra of the RuCl(6)(2-) and OsCl(6)(2-) complexes has been developed for the determination of osmium in a mixture with ruthenium. The interfering effect of ruthenium on the determination of osmium can be eliminated by measuring the value of a third-order derivative spectrum of the OsCl(6)(2-) complex at 350.0 nm ("zero-crossing point" of ruthenium). Simple and rapid determination of ruthenium and osmium in a calibration standard solution of the noble metals (Ru, Rh, Pd, Os, Ir, Pt and Au) for plasma spectroscopy using the proposed methods has been achieved.     

Optosensing properties of fac-Re(CO)(3)(dpknph)Cl (dpknph=di-2-pyridyl ketone p-nitrophenyl hydrazone)

Optical and thermodynamic measurements on fac-Re(CO)(3)(dpknph)Cl in polar non aqueous solvents revealed the existence of two interlocked conformational forms for fac-Re(CO)(3)(dpknph)Cl. The equilibrium distribution of the low (alpha-) and high (beta-) energy conformations is solvent dependent, controlled by the dipole moment of the solvent molecules and their orientation around the total dipole of fac-Re(CO)(3)(dpknph)Cl. The interplay between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, allowed calculations of their extinction coefficients, by forcing the equilibrium to shift to one conformation, using chemical stimuli. In DMSO and DMF extinction coefficients of 87 000+/-2000 and 35 000+/-2000 M(-1) cm(-1) were calculated for the beta- and alpha-conformations of fac-Re(CO)(3)(dpknph)Cl at lambda(max.), respectively. Thermo-optical measurements on fac-Re(CO)(3)(dpknph)Cl, allowed calculations of the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl. In DMSO and DMF changes in enthalpy (DeltaH(?)) of -11.2+/-1.3 and 10.9+/-0.5 kJmol(-1), entropy (DeltaS(?)) of -12.7+/-4.3 and 29.4+/-1.7 JK(-1) mol(-1), and free energy (DeltaG(?)) of -7.5+/-0.2 and+2.2+/-0.2 kJmol(-1) and hence equilibrium constants of 20.9+/-1.7 and 0.4+/-0.1 were calculated for fac-Re(CO)(3)(dpknph) at 295 K. The high values for the extinction coefficients and low values for the activation parameters for the interconversion between the alpha- and beta-conformations of fac-Re(CO)(3)(dpknph)Cl, in polar non aqueous solvents allowed the use of these systems as molecular sensors to probe their structural relaxation and interactions with their surroundings. These systems (fac-Re(CO)(3)(dpknph)Cl and surrounding solvent molecules) optically sense chemical and physical stimuli and their sensing power depends on the intensity and nature of these stimuli, i.e. the systems exhibit a high degree of sensitivity and selectivity.