Electronic Absorption Studies Research Articles

Hole mediated coupling in Sr2Nb2O7 for visible light photocatalysis

The band gap reduction and effective utilization of visible solar light are possible by introducing the anionic hole-hole mediated coupling in Sr(2)Nb(2)O(7). By using the first principles calculations, we have investigated the mono- and co-anionic doping (S, N and C) in layered perovskite Sr(2)Nb(2)O(7) for the visible-light photocatalysis. Our electronic structure and optical absorption study shows that the mono- (N and S) and co-anionic doped (N-N and C-S) Sr(2)Nb(2)O(7) systems are promising materials for the visible light photocatalysis. The calculated binding energies show that if the hole-hole mediated coupling could be introduced, the co-doped systems would be more stable than their respective mono-doped systems. Optical absorption curves indicate that doping S, (N-N) and (C-S) in Sr(2)Nb(2)O(7) can harvest a longer wavelength of the visible light spectrum as compared to the pure Sr(2)Nb(2)O(7) for efficient photocatalysis.

Facile synthesis and optical properties of magic-number Au13 clusters

Synthesis of molecular gold clusters through a post-synthetic scheme involving HCl-promoted nuclearity convergence was examined with various phosphine ligands. Systematic studies with a series of bis(diphenylphosphino) ligands (Ph(2)P-(CH(2))(m)-PPh(2)) using electrospray ionization mass spectrometry (ESI-MS) and electronic absorption spectroscopy demonstrated that the use of dppp (m = 3), dppb (m = 4) and dpppe (m = 5) as the ligands resulted in the formation of [Au(13)P(8)Cl(4)](+) type clusters, whereas the [Au(13)P(10)Cl(2)](3+) type cluster was formed with dppe (m = 2). The cluster species did not survive the HCl treatment step when monophosphines PPh(3), PMe(2)Ph, and POct(3) were employed, but [Au(13)(POct(3))(8)Cl(4)](+) was isolated as a minor product in the NaBH(4) reduction of Au(POct(3))Cl in aqueous THF. Electronic absorption and photoluminescence studies of a series of Au(13) clusters revealed that their optical properties are highly dependent on the phosphine/chloride composition ratio, but are far less so on the phosphine structure.

Synthesis and electronic absorption studies of novel (trifluoromethyl)phenoxy-substituted phthalocyanines

The reaction of 4-[4-(trifluoromethyl)phenoxy]phenol with 4-nitrophthalonitrile in the presence of K2CO3 leads to formation of 4-[4-[4-(trifluoromethyl)phenoxy]phenoxy]phthalonitrile. Tetrakis[4-[4-(trifluoromethyl)phenoxy]phenoxy]-substituted metal-free phthalocyanine was achieved by tetramerization of the phthalonitrile in 2-(dimethylamino)ethanol, whereas metallophthalocyanines were prepared in the presence of zinc, cobalt, or copper salts. These compounds show high solubility in weakly and medium polar solvents, in strongly polar solvents (dimethylformamide, dimethylsulfoxide), and in aromatic hydrocarbons (toluene, benzene). The new phthalocyanines were characterized by elemental analyses, 1H nuclear magnetic resonance (NMR), 13C NMR, 19F NMR, ultraviolet-visible (UV-Vis), Fourier-transform infrared (FT-IR), and mass spectroscopic methods.

Fluorescent Zinc(II) Complex Exhibiting “On-Off-On” Switching Toward Cu2+ and Ag+ Ions

Binuclear zinc(II) and copper(II) complexes based on a new Schiff base ligand N,N'-bis(2-hydroxybenzilidene)-2,4,6-trimethylbenzene-1,3-diamine (H(2)L) have been synthesized. The ligand H(2)L and complexes under investigation have been characterized by elemental analyses, spectral (FT-IR, (1)H, (13)C NMR, ESI-MS, electronic absorption, emission), and electrochemical studies. The structures of H(2)L and complexes [{Zn(C(23)H(18)N(2)O(2))}(2)] (1) and [{Cu(C(23)H(18)N(2)O(2))}(2)]·H(2)O (2) have been determined crystallographically. Selective "On-Off-On" switching behavior of the fluorescent complex 1 has been studied. The fluorescence intensity of 1 quenches (turns-off) upon addition of Cu(2+), while enhances (turns-on) in the presence of Ag(+) ions. The mechanisms of "On-Off-On" signaling have been supported by (1)H NMR, ESI-MS, electronic absorption, and emission spectral studies. Job's plot analysis supported 1:1 and 1:2 stoichiometries for Cu(2+) and Ag(+) ions, respectively. Association and quenching constants have been estimated by the Benesi-Hildebrand method and Stern-Volmer plot. Moreover, 1 mimics a molecular keypad lock that follows correct chemical input order to give maximum output signal.

Evidence of the Controlled Interaction between PEDOT and PSS in the PEDOT:PSS Complex via Concentration Changes of the Complex Solution

Photoluminescence, electronic absorption, and pH studies of a poly(ethylene-3,4-dioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) dispersion as a function of the PEDOT:PSS concentration are shown to provide a better understanding of the effect of PSS on the intramolecular conductivity of PEDOT chains. Particularly, concentration changes of PEDOT:PSS were found to be accompanied with different extents of dissociation of protons in the solution and different charge states of PSS chains, respectively, which affect the electrostatic interaction between PSS and PEDOT and intramolecular conductivity in the PEDOT backbone.

Synthesis and Characterization of Some Group 12 Metal Complexes with Tellurium Containing 10‐Membered Tetraazamacrocyclic Ligands

A new series of 10‐membered tellurium containing tetraazamacrocyclic complexes, [ML1Cl2], [ML2Cl2] and [ML3Cl2], where [M=Zn(II), Cd(II), Hg(II); L1, L2 and L3=10‐membered tellurium containing tetraazamacrocyclic ligands] have been prepared via the template condensation of ethylenediamine and diaryltellurium dichlorides, R2TeCl2, (R=p‐hydroxyphenyl, 3‐methyl‐4‐hydroxyphenyl, p‐methoxyphenyl) in the presence of metal chlorides. These complexes have been characterized by elemental analyses, conductivity measurements, infrared, electronic absorption and proton magnetic resonance spectral studies. IR and PMR spectra confirm the formation of 10‐membered tetraazamacrocycle skeleton and their tetradentate nature. An octahedral geometry has been assigned to all the metal complexes on the basis of various physicochemical studies.

Design, Synthesis, Photophysics, and Anion-Binding Studies of Bis(dicyclohexylphosphino)methane-Containing Dinuclear Gold(I) Thiolate Complexes with Urea Receptors

A series of bis(dicyclohexylphosphino)methane (dcpm)-containing gold(I) thiolate complexes with urea receptors, 1-3, has been successfully designed and synthesized, and their photophysical and anion-binding properties have been studied. The linker between the thiolate and the urea group, and the electronic environment of the urea moiety, have been found to exert a great influence on the photophysical and anion-binding properties of the complexes. Complex 3 displays an intense long-lived orange-red luminescence at around 620 nm in the solid state and in the glass state at 77 K, which is considerably red shifted from the band seen in a solution of dichloromethane at room temperature, suggesting the presence of AuAu interactions. Upon introducing an electron-withdrawing NO(2) group, complex 1 was found to show high selectivity and sensitivity for F(-) through a drastic color change from yellow to red. The anion-binding constants of the complexes have been determined from electronic absorption and (1)H NMR spectroscopy titration studies and the data were found to fit well to a 1:1 binding model for the interactions between the complexes and the anions. Complexes 1 and 2 show the same anion selectivity trend of F(-) > AcO(-) > H(2)PO(4)(-) > Cl(-) approximately Br(-) approximately I(-), which is consistent with the trend in anion basicity. In addition, complex 1 has been shown to exhibit higher binding affinity for anions compared with those of complexes 2 and 3, probably due to the higher acidity of the urea moiety as a result of the introduction of the NO(2) group.

Half-sandwich ruthenium, rhodium and iridium complexes containing dipyridyl amine based ligands

Compounds derived from the reactions of dimeric arene ruthenium [{( η 6-arene)Ru( μ-Cl)Cl} 2] (arene = benzene and p-cymene) and structurally analogous rhodium and iridium complexes [{( η 5-C 5Me 5)M( μ-Cl)Cl} 2] (M = Rh or Ir) with 2-chloro-4,6-(di-2-pyridylamino)-1,3,5-triazine (cddt) and 2,4,6-tris(di-2-pyridylamino)-1,3,5-triazine (tdat) are reported. Compounds under investigation have been characterized by elemental analyses, NMR ( 1H and 13C), electronic absorption, emission spectral and electrochemical studies. Structures of the dinuclear compounds [{( η 6-C 10H 14)RuCl} 2(cddt)](PF 6) 2, [{( η 5-C 5Me 5)RhCl} 2(cddt)]Cl 2·6H 2O and trinuclear compound [{( η 6-C 6H 6)RuCl} 3(tdat)]Cl 3·4H 2O have been determined crystallographically. Among cddt containing compounds the {( η 6-C 10H 14)RuCl}- units in [{( η 6-C 10H 14)RuCl} 2(cddt)](PF 6) 2 are anti, while {( η 5-C 5Me 5)RhCl}- in the rhodium compound [{( η 5-C 5Me 5)RhCl} 2(cddt)]Cl 2·6H 2O are syn with respect to triazine ring. Cyclic voltammetric studies on the compounds suggested lack of communication between the metal centres. Furthermore, although tdat is luminescent at room temperature compounds under investigation containing this ligand are non-luminescent in acetonitrile.

Photophysics in solution and Langmuir–Blodgett film and vapochromic behavior of the Pt(ii) 2,6-bis(N-alkylbenzimidazol-2′-yl)pyridine complexes with different alkyl chains and counter anions

A systematic photophysical study, i.e. electronic absorption and emission study, on platinum(II) 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine complexes with different alkyl chains and different anions were performed in solutions and in Langmuir-Blodgett (LB) films. Electronic absorption in solution shows high-energy bands that are assigned to pi,pi* transitions within the ligand and a moderately intense metal-to-ligand charge transfer ((1)MLCT) band above 400 nm. All the complexes are emissive at room temperature and at 77 K. When low-polarity solvent, such as hexane was added to the CHCl(3) solutions of these complexes, solvent-induced aggregation occurred, which was evident by the appearance of a broad metal-metal-to-ligand charge transfer ((1)MMLCT) band between 500 and 600 nm in their UV-vis spectra and a new emission band appearing around 670 nm, which is attributed to the (3)MMLCT state. The degree of aggregation is affected drastically by the nature of the counter anion, with complexes 5b, 5c and 5d that contain PF(6)(-), ClO(4)(-) and BF(4)(-) anion, respectively, appearing to more readily aggregate. In contrast, the length of the alkyl chain shows a negligible effect on the degree of aggregation. The emission lifetime measurements further confirm the formation of aggregates. These complexes exhibited selective vapochromic response when exposed to volatile organic compounds (VOCs). Both the alkyl chain length and the counter anion affect the vapochromic effect. Moreover, LB films were fabricated using these amphiphilic platinum complexes and most of the films displayed (3)MMLCT emission. The emission energy and the lifetime in LB films are influenced significantly by the counter anions. Complex 5f mainly emits from a ligand-ligand pi-pi interacted excited state, and 5a-5e exhibit a (3)MMLCT emission. Although no simple systematic correlation could be made between the nature of the counter ion and the electronic absorption and/or emission properties of these platinum complexes in solution and in LB films, we believe that the salient counter ion effects are most likely related to the size and shape of the counter ions.

Electronic absorption study on acid–base equilibria for some pyrimidine derivatives containing semi- and thiosemicarbazone moiety

The UV–vis spectra of recently synthesized 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-one, ( I), and 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-thione, ( II) were studied in aqueous methanol (5%, v/v methanol). The nature of the electronic transitions and the roles of carbonyl oxygen of I and thiocarbonyl sulfur of II on the behavior of UV–vis spectra were discussed. Acid–base equilibria of the compounds against varying pH and p K a values related equilibria were determined at an ionic strength of 0.10 M by using the Henderson–Haselbalch equation. The mean acidity constants for the protonated forms of the compounds were determined as p K a1 = 5.121, p K a2 = 7.929 and p K a3 = 11.130 for I and p K a1 = 4.684, p K a2 = 7.245 and p K a3 = 10.630 for II. The preferred dissociation mechanisms were discussed based on UV–vis data and a mechanism was proposed for each compound.

Synthesis, characterisation and theoretical studies on some piano-stool ruthenium and rhodium complexes containing substituted phenyl imidazole ligands

Reactions of the chloro-bridged arene ruthenium complexes [{(η 6 -arene)RuCl(μ-Cl} 2 ] (η 6 -arene = benzene, p -cymene) and structurally analogous rhodium complex [{(η 5 -C 5 Me 5 )RhCl(μ-Cl} 2 ] with imidazole based ligands viz., 1-(4-nitro-phenyl)-imidazole (NOPI), 1-(4-formylphenyl)-imidazole (FPI) and 1-(4-hydroxyphenyl)-imidazole (HPI) have been investigated. The resulting complexes have been characterised by elemental analyses, IR, 1 H and 13 C NMR, electronic absorption and emission spectral studies. Crystal structure of the representative complex [(η 5 -C 5 Me 5 )RhCl 2 (NOPI)] has been determined crystallographically. Geometrical optimisation on the complexes have been performed using exchange correlation functional B3LYP. Optimised bond lengths and angles of the complexes have been found to be in good agreement with our earlier reports and single crystal X-ray data of the complex [(η 5 -C 5 Me 5 )RhCl 2 (NOPI)].

Unsymmetrical FeIIICoII and GaIIICoII Complexes as Chemical Hydrolases: Biomimetic Models for Purple Acid Phosphatases (PAPs)

The design and development of suitable biomimetic catalytic systems capable of mimicking the functional properties of enzymes continues to be a challenge for bioinorganic chemists. In this study, we report on the synthesis, X-ray structures, and physicochemical characterization of the novel isostructural [Fe(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (1) and [Ga(III)Co(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (2) complexes with the unsymmetrical dinucleating ligand H(2)BPBPMP (2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol). The previously reported complex [Fe(III)Zn(II)(BPBPMP)(mu-OAc)(2)]ClO(4) (3) was investigated here by electron paramagnetic resonance for comparison with such studies on 1 and 2. A magneto-structural correlation between the exchange parameter J (cm(-1)) and the average bond lengh d (A) of the [Fe(III)-O-M(II)] structural unit for 1 and for related isostructural Fe(III)M(II) complexes using the correlation J = -10(7) exp(-6.8d) reveals that this parameter is the major factor that determines the degree of antiferromagnetic coupling in the series [(BPBPMP)Fe(III)(mu-OAc)(2)M(II)](+) (M(II) = Mn, Fe, Co, Ni) of complexes. Potentiometric and spectrophotometric titrations along with electronic absorption studies show that, in aqueous solution, complexes 1 and 2 generate the [(HO)M(III)(mu-OH)Co(II)(H(2)O)] complex as the catalytically active species in diester hydrolysis reactions. Kinetic studies on the hydrolysis of the model substrate bis(2,4-dinitrophenyl)phosphate by 1 and 2 show Michaelis-Menten behavior, with 2 being 35% more active than 1. In combination with k(H)/k(D) isotope effects, the kinetic studies suggest a mechanism in which a terminal M(III)-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst. In addition, the complexes show maximum catalytic activity in DNA hydrolysis near physiological pH. The modest reactivity difference between 1 and 2 is consistent with the slightly increased nucleophilic character of the Ga(III)-OH terminal group in comparison to Fe(III)-OH in the dinuclear M(III)Co(II) species.

Rare monomeric structure of CpRh(III) dithiolene complex: Combined ESR and electronic absorption studies on electrochemically generated Rh(II) species

Abstract The [CpRhIII(mnt)] (1) (Cp = η5-cyclopentadienyl, mnt = maleonitrile-1,2-dithiolate) was characterized as a rare monomeric structure. The CV of 1 showed a reversible reduction wave which attributed to Rh(II)/Rh(III) couple. UV–Vis spectral measurement during electrolysis using an OTTLE cell indicated that lifetime of electrochemically generated 1 − (Rh(II) species) was only a few seconds. Isotropic (giso = 2.045, Aiso = 1.15 mT) and anisotropic ESR (g1 = 2.173, a1 = 1.85 mT, g2 = 1.982, a2 = 0.98 mT) spectra of 1 − were observed while electrochemical reduction of 1. Both ESR spectra showed hyperfine splittings due to the central Rh (I = 1/2).

The Microwave-assisted syntheses and a conductivity study of a platinum phthalocyanine and its derivatives

The parent platinum phthalocyanine (PtPc) and its derivatives with tetranitro (PtTNPc) and tetramine (PtTAPc) on the peripheral benzene were synthesized in the pure state for the first time by microwave irradiation. These complexes were characterized using physico-chemical methods like elemental, electronic absorption, IR spectral, magnetic susceptibility, thermogravimetry and X-ray powder diffraction studies. Kinetic and thermodynamic parameters associated with the thermal decomposition were calculated using the thermogravimetric analytical data. Electrical conductivity studies were carried out using the two-probe technique in the temperature range 298–473 K for each complex to study the effect of the donor and acceptor substituents on the platinum phthalocyanine macrocycle. The electrical conductivities observed at room temperature are in the order PtTAPc > PtTNPc > PtPc. The improvement in the intrinsic electrical conductivity of PtTAPc is due to the electron donating amine substituents which are expected to facilitate greater intermolecular contact and increase interactions, providing a greater pathway for charge carriers.

Nanolayers of selected porphyrin and phthalocyanine dyes on solid substrates studied by electronic absorption and IR reflection–absorption spectroscopy

Electronic absorption and IR reflection–absorption spectra in non-polarized and in polarized light for lead porphyrin as well as magnesium and lead phthalocyanine dyes when deposited in the form of Langmuir–Blodgett (LB) nanolayers on solid inorganic surfaces (quartz, semiconductor and metal) were measured. Some IR bands of the Langmuir–Blodgett dye layers’ spectra show frequency shifts and changes in the relative intensities as well as in half widths when compared with the vibrational features of powdered dyes dispersed in KBr pellets, which were used as references. The FT-IR spectroscopic examination of the Langmuir–Blodgett layers allowed to estimate electron redistribution at the interface between dye layer and solid substrates. The Langmuir–Blodgett films of different thicknesses (3, 5, 10 layers) were studied at various angles of IR beam incidence and different light polarizations. The most spectacular results were obtained for the grazing incidence (80°) and films of 5 layers for dyes on the Au substrate. The IR spectroscopy was supported with electronic absorption studies (UV–vis) to follow interaction at interface between the dye layers and the substrates as well as to evaluate linear dichroism and to determine arrangement of molecules in the Langmuir–Blodgett films. Molecular arrangement in the Langmuir–Blodgett layers was discussed. It was shown that the dye molecular planes are rather randomly oriented in the Langmuir–Blodgett films with a tendency that the Q y and Q x transition moments in the phthalocyanine macroring are slightly directed along the y-axis (Langmuir–Blodgett dipping direction) and the x-axis direction, respectively.

Synthesis and characterization of water-soluble zinc(II) Schiff-base complexes derived from amino acids and 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride

Tridentate Schiff-base ligands derived from condensation of 3-formyl-4-hydroxybenzyl-triphenylphosphonium chloride with glycine, L-alanine, L-valine, L-leucine and L-phenylalanine in the presence of Zn(OAc)2 · 2H2O form five new water-soluble Zn(II) complexes, which were characterized by elemental analyses, IR, electronic absorption and 1H, 13C NMR spectroscopies. In the IR spectra of the complexes, the difference between the asymmetric and the symmetric carboxylate stretching frequencies is larger than ∼210 cm−1, which implies that the carboxylate groups are monodentate. UV-Vis electronic absorption studies show that Zn(II) functions as a trap for the Schiff-base intermediate. Schiff-base complexes formation were confirmed by the appearance of new signals in the 1H NMR for the azomethine hydrogen at ∼8 ppm and condensed L-amino acids at 3.4–3.8 ppm (C(3)–H). These complexes are formed through coordination of the ONO from the carboxyl, imino and phenoxy groups of the ligands to Zn(II).

Interaction of pyrimethamine and sulfadiazine with ionic and neutral micelles: Electronic absorption and fluorescence studies

The binding of two antitoxoplasmosis drugs, pyrimethamine (PYR) and sulfadiazine (SDZ) to cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS), zwiterionic N-hexadecyl- N, N-dimethyl-2-ammonium-1-propanesulfonate (HPS) and neutral polyoxyethylene-dodecyl-ether (Brij-35 ®) micelles was studied using absorption and fluorescence spectroscopic methods. The p K a of PYR changed in the presence of charged anionic, cationic and zwiterionic micelles, indicating that interaction is influenced by the micellar charge. For SDZ, p K a changes were lower than 1 for all micelles, suggesting the occurrence of low binding constants in addition to a reasonable influence of the micellar charge. The values of binding constants K b, obtained from fluorescence measurements, for PYR to CTAC micelles were very low at pH 4.0, where the drug is in a complete protonated state, increasing at pH 9.0 to long-chained CTAC and HPS micelles since this factor also favors accomodation of the neutral drug in the hydrophobic compartments. For SDZ the binding constants were determined from optical absorption measurements. Low binding constants were observed to charged surfactant micelles, with influence of micellar charge. It must be stated however that those values can be underestimated due to the relatively low sensitivity of the method based on absorption measurements.

Syntheses, Electronic Absorption, Emission, and Ion-Binding Studies of Platinum(II) C^N^C and Terpyridyl Complexes Containing Crown Ether Pendants

Yam et al. have recently established a more accurate equation (Organometallics 2007, 26, 6091–6098) for determining the binding constants K11 and K21 in systems that involve the complexation of metal ions in both 1:1 and 2:1 stoichiometry and would like to update the data found in Chem. Eur. J. 2002, 8, 4066–4076. From the fitting of the revised equation, the binding constants of [Pt(C^N^C)(pyCCB15C5) (5) and [Pt(trpy)(pyCCB15C5)](PF6)2 (9) (HC^N^CH= 2,6-diphenylpyridine, dppy; CB15C5= benzo[15]crown-5; trpy= 2,2′:6′,2′′-terpyridine) to K+ in 1:1 and 2:1 stoichiometries were obtained. In solution (CH3CN/DMF; 8:2 v/v), the log K11 and log K21 values of 5 were found to be 2.73 and 3.01, respectively, whereas those of 9 were 1.73 and 1.78, respectively. The corresponding log K11 and log K21 values of 9 in acetonitrile were 3.40 and 3.13, respectively. In view of the slight or insignificant changes of these values, both the discussions and conclusion remain unchanged and are therefore retained. The authors would like to apologize for any inconvenience caused.

Resonance Raman and electronic absorption study of free‐base tetraphenylporphine diacid dispersed in polymethylcyanoacrylate

AbstractWe report a resonance Raman study on free‐base tetraphenylporphine (H2TPP) and its chemically prepared diacid dispersed in polymethylcyanoacrylate (PMCA). Photoexcitation of the neutral porphine by laser light leads irreversibly to the formation of the diacid, with the π‐cation radical as intermediate species. Resonance Raman (RR) spectra of the diacid dispersed in the polymer obtained with 441.6 nm in the wavenumber region of 100–1650 cm−1 are recorded. Wavenumbers with other excitation lines are also reported for the diacid species. Some bands assigned to out‐of‐plane vibrational modes and forbidden under ideal D2h symmetry are also observed in the resonance Raman spectra of the diacid. These bands arise from the out‐of‐plane distortions, which reduce the symmetry of the molecule. These findings are supported by the electronic absorption studies of the diacid in the polymer. Copyright © 2007 John Wiley & Sons, Ltd.

Wavelength Dependant Quenching of 2,5-Diphenyloxazole Fluorescence by Nucleotides

The quenching of 2,5-diphenyloxazole (PPO) fluorescence by nucleotides has been investigated by electronic absorption and steady state fluorescence spectra. Five purine nucleotides AMP, ADP, ATP, GMP and dGMP, one pyrimidine nucleotide UMP and one dinucleotide NAD have been employed in the present study. Electronic absorption studies indicate that there is no ground state complexation between the nucleotides and PPO. The quenching of PPO fluorescence was investigated at two different wavelengths. When excited at 304 nm, the lambda(max) of PPO, the fluorescence spectra of PPO is quenched following Stern-Volmer kinetics. The quenching ability of nucleotides are in the order NAD>AMP>ADP>GMP>dGMP>UMP. The K(SV) and k(q) values obtained indicate that AMP is a better quencher of PPO fluorescence than GMP, which is contrary to commonly observed pattern. The quenching is found to be dynamic in nature. However, when excited at 260 nm, the absorption maximum of the nucleotides, the fluorescence intensity of PPO is reduced with increase in the concentration of the nucleotide. This is attributed to the primary inner filter effect arising due to the absorption of the incident radiation by the nucleotides. Thus the inner filter effect phenomenon can be employed to assay the non-fluorescent molecules by fluorimetry.