Solvent and Media Effects on the Photophysics of Naphthoxazole Derivatives

The photophysical properties of 2‐phenyl‐naphtho[1,2‐d][1,3]oxazole, 2(4‐N,N‐dimethylaminophenyl)naphtho[1,2‐d][1,3]oxazole and 2(4‐N,N‐diphenylaminophenyl) naphtho[1,2‐d][1,3]oxazole were studied in a series of solvents. UV–Vis absorption spectra are insensitive to solvent polarity whereas the fluorescence spectra in the same solvent set show an important solvatochromic effect leading to large Stokes shifts. Linear solvation energy relationships were employed to correlate the position of fluorescence spectra maxima with microscopic empirical solvent parameters. This study indicates that important intramolecular charge transfer takes place during the excitation process. In addition, an analysis of the solvatochromic behavior of the UV–Vis absorption and fluorescence spectra in terms of the Lippert–Mataga equation shows a large increase in the excited‐state dipole moment, which is also compatible with the formation of an intramolecular charge‐transfer excited state. We propose both naphthoxazole derivatives as suitable fluorescent probes to determine physicochemical microproperties in several systems and as dyes in dye lasers; consequence of their high fluorescence quantum yields in most solvents, their large molar absorption coefficients, with fluorescence lifetimes in the range 1–3 ns as well as their high photostability.     

Solvatochromic parameters for binary mixtures of 1-(1-butyl)-3-methylimidazolium tetrafluoroborate with some protic molecular solvents

The solvatochromic parameters (ET(N), normalized polarity parameter; pi*, dipolarity/polarizability; beta, hydrogen-bond acceptor basicity; alpha, hydrogen-bond donor acidity) were determined for binary solvent mixtures of 1-(1-butyl)-3-methylimidazolium tetrafluoroborate ([bmim]BF4) with water, methanol, and ethanol at 25 degrees C over the whole range of mole fractions. In nonaqueous solutions, the value of the mixture increases with mole the fraction of [bmim]BF4 and then decreases gradually to the value of pure [bmim]BF4. Positive deviation from ideal behavior was observed for the solvent parameters ET(N), pi*, and alpha, whereas the deviation of the beta parameter is negative. The applicability of the combined nearly ideal binary solvent/Redlich-Kister equation for the correlation of various solvatochromic parameters with solvent composition was proved too for the first time. This equation provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute-solvent and solvent-solvent interactions have been applied for interpretation of the results.     

Stereoselective synthesis of and atropisomerism in 4-pyridyl-3-(1-pyridinio)-3,4-trans-1,2,3,4-tetrahydropyridines and their transformation products

A series of 2-oxo-4-pyridyl-3-(1-pyridinio)-5-cyano-3,4-trans-1,2,3,4-tetrahydropyridine-6-6-olates were prepared by condensation of pyridinium ylides with α,β-unsaturated carbonyl compounds or more conveniently by a three-component condensation of pyridinium ylides, pyridine aldehydes, and ethyl cyanoacetate 3 and/or 6 . This analogues of the above tetrahydropyridines were prepared in a similar way starting from suitable substrates. Spectroscopic data revealed that the reaction leads to trans-isomers around the C³-C⁴ bond and is atroposelective. The conformation of and tautomerism in the tetrahydropyridines are discussed in the light of ¹H NMR data. The reaction of 5-cyano-3-(3-methyl-1-pyridinio)-2-oxo-4-(3-pyridyl)-1,2,3,4-tetrahydropyridine-6-thiolate 10c with phenacyl bromide was found to give 3-hydroxy-5-oxo-7-(3-pyridyl)-6-(3-methyl-1-pyridinio)-3-phenyl-8-cyano-6,7-trans-2,3,6,7-tetrahydrothiazol[3,2a]pyridine bromide, the crystal and molecular structure of which has been determined by X-ray crystallographic analysis.     

Solvatochromism of 3-[2-(4-diphenylaminophenyl)benzoxazol-5-yl]alanine methyl ester. A new fluorescence probe

The photophysical properties of 3-[2-(4-diphenylaminophenyl)benzoxazol-5-yl]alanine methyl ester (1b) and its Boc derivative (1a) were studied in a series of solvents. Its UV-Vis absorption spectra are less sensitive to the solvent polarity than the corresponding fluorescence spectra which show pronounced solvatochromic effect leading to large Stokes shifts. Using an efficient solvatochromic method, based on the molecular-microscopic empirical solvent polarity parameter E(T)(N), a large change of the dipole moment on excitation has been found. From an analysis of the solvatochromic behaviour of the UV-Vis absorption and fluorescence spectra in terms of bulk solvent polarity functions, f(epsilon(r),n) and g(n), a large excited-state dipole moment (mu(e) = 11D), almost perpendicular to the smaller ground-state dipole moment, was observed. This demonstrates the formation of an intramolecular charge-transfer excited state. Large changes of the fluorescence quantum yields as well as the fluorescence lifetimes with an increase of a solvent polarity cause that the new non-proteinogenic amino acid, 3-[2-(4-diphenylaminophenyl)benzoxazol-5-yl]-alanine methyl ester, is a new useful fluorescence probe for biophysical studies of peptides and proteins.     

Merocyanine solvatochromic dyes in the study of synergistic effects in mixtures of chloroform with hydrogen-bond accepting solvents

The molar transition energy (E(T)) polarity values for the solvatochromic probes 2,6-diphenyl-4-(2,4,6-triphenylpyridinium)phenolate (1), 4[(1-methyl-4-(1H)-pyridinylidene)-ethylidene]-2,5-cyclohexadien-1-one (2), and 4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (3) were collected in binary mixtures comprising chloroform and a hydrogen-bond accepting (HBA) solvent [dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), acetone or acetonitrile], aiming to investigate the ability of the chlorinated component to act as hydrogen-bond donating (HBD) solvent. Plots of E(T) as a function of X(2), the mole fraction of chloroform, were obtained and the data were analysed to investigate the preferential solvation (PS) of each probe in terms of both solute-solvent and solvent-solvent interactions. For dyes 1 and 2 a strong synergistic behavior was observed for all mixtures studied, indicating that the dyes are preferentially solvated by complexes formed through hydrogen bonding between chloroform and the HBA component in the mixtures. A study of 1 in deuterated chloroform with an HBA component (DMF and DMA) demonstrated that while almost no differences occur with the DMF mixtures, the presence of deuterated chloroform in its mixtures with DMA increases the synergistic effect, suggesting that it interacts more strongly with DMA, making its mixtures more polar. These data were successfully fitted to a model based on solvent-exchange equilibria. The features of the mixtures with dye 3 revealed a very different profile in comparison with the other two dyes, which suggests that in mixtures containing chloroform, the microenvironment of the dye seems to be important in determining the contribution of the structure resonances responsible for the stability of the dye.     

Testing computational models of hyperpolarizability in a merocyanine dye using spectroscopic and DFT methods

The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.     

Merocyanine-type dyes from barbituric acid derivatives.

The preparation and the solvatochromic behavior of two dyes, obtained by condensation of N,N'-dimethylbarbituric acid with dimethylaminobenzaldehyde and with 4,4'-bis(N,N-dimethylamino)benzophenone (Michler's ketone) are described. The latter dye is rather sensitive to the polarity of the medium, and in particular, to the hydrogen-bond-donor ability of protic solvents. The solvatochromism of both compounds is discussed in terms of the pi* and E(T)(30) solvent polarity scales and their differences in behavior interpreted with the aid of semiempirical calculations.     

Development of a quinoxaline-based fluorescent probe for quantitative estimation of protein binding site polarity

The compound 2-[(1E)-2-(1H-pyrrol-2-yl)ethenyl]-quinoxaline (PQX) is a promising fluorescent chromophore for the estimation of protein binding site polarity, due to its full-color solvatochromic fluorescence. A linear relationship was obtained between the peak emission wavenumber and E(T)(N) (normalized solvent polarity). The BSA binding site polarity was estimated from the solvatochromic plot.     

Isomeric [2]rotaxanes and unidirectional [2]pseudorotaxane composed of alpha-cyclodextrin and aliphatic chain-linked carbazole-viologen compounds

[structure: see text] Capping the alpha-cyclodextrin (alpha-CD) complex of 1-(N-carbazole)-10-[4-(4-pyridinio)-1-pyridinio]decane with 3,5-dimethoxybenzyl bromide in DMF gives two isomeric [2]rotaxanes, 2a and 2b, while alpha-CD and 1-(N-carbazole)-10-[4-(1-methyl-4-pyridnino)-1-pyridinio]decane 3 in water form mostly a unidirectional [2]pseudorotaxane having the same alpha-CD orientation as 2b. Structures were elucidated from 1H NMR and circular dichroism spectra. The orientational specificity of alpha-CD in the 3/alpha-CD [2]pseudorotaxane is due to the slow dethreading rate of the 2b-type isomer.     

Regio- and stereoselective synthesis of tetrahydroindolysines,tetrahydropyridin-6-olates,and cyclopropanes from pyridinium ylides and unsaturated nitriles

The regio- and stereoselectivity of the reactions of pyridinium ylides with unsaturated nitriles are dependent on the electronic nature of the substituent in position 3 of the pyridine ring. The reaction of 1-carbamoylmethylide-3-cyanopyridinium with arylmethylenemalononitriles or arylmethylcyanoacetic esters proceeds regio- and stereoselectively with the formation of substituted 2-aryl-3-carbamoyl-6-cyano-2,3-trans- or 2,3-cis-1,2,3,8a-tetrahydroindolysines. The condensation of pyridinium 1-carbamoylmethylide with arylmethylenecyanoacetic ether leads to 4-aryl-2-oxo-3-(1-pyridinio)-5-cyano-3,4-trans-1,2,3,4-tetrahydropyridin-6-olates. The reaction of pyridinium (3-methylpyridinium) 1-carbamoylmethylide with arylmethylenemalononitriles results in the formation of 2-aryl-1,1-dicyano-3-carbamoyl-3-(1-pyridinio)- or (3-methyl-1-pyridinio)-1-propanides, which undergo stereoselective 1,3-transelimination with the formation of 3-aryl-1,1-dicyano-2-carbamoylcyclopropanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 146–155. January, 1991.     

Reversal in solvatochromism in some novel styrylpyridinium dyes having a hydrophobic cleft

The influence of solvent polarity on the electronic transition of four different N-hexadecyl styrylpyridinium dyes has been investigated in 15 solvents. The E(T)(30) scale has been used to propose a quantitative approach towards the relative stability of the electronic ground and excited state species. The extents of contribution of dipolar aprotic solvents towards the solvation of the excited species have been determined to be 42-48% for some of the dyes. Instead of a steady solvatochromism, all the dyes suffer a reversal in solvatochromism. The transitions of the solvatochromism, referred to as solvatochromic switches, are found to be at E(T)(30) values of approximately 50 for methyl and N,N-dimethylamino substituted dyes while at 37.6 for hydroxyl substituted dye and approximately 45 for 4-(1-methyl-2-phenylethenyl) pyridinium dye. A reversal in the trend of solvent effect in the later dye corresponding to 4-(4-methyl styryl)pyridinium dye has been attributed to an analogy of series and parallel electron flow.     

Determination of solvatochromic solvent polarity parameters for the characterisation of some nematic liquid crystal in anisotropic and isotropic phases

Characterisation of liquid crystals (LCs) as solvents is needed, to obtain the polarity and solvatochromic polarity parameters of these media. Polarity parameters demonstrate the effects of LC media on the photo-physical behaviour of solute molecules in an anisotropic medium. The practical limitations in determining solvent polarity scale parameters for LCs can overcome the overlapping absorption band of LCs and solvent-sensitive standard compounds or their insolubility in LCs. In this work, we report Kamlet–Abboud–Taft polarity functions of some nematic LCs in different temperatures and phases, isotropic and anisotropic, with the solvatochromic method, using the Reichardt's dye and 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-phenolate standard probe. In addition, a new azo and coumarin dye were used as probes to obtain some solvatochromic polarity parameters. Finally, a new polarity parameter, the LC anisotropic matrix, is introduced.     

Solvatochromism of 3-[2-(aryl)benzoxazol-5-yl]alanine derivatives

The photophysical properties of N-Boc-3-[2-(9-anthryl)benzoxazol-5-yl]-l-alanine methyl ester (BoxAnt) and N-Boc-3-[2-[4-(9′-(10′-butyl)anthryl)phenyl]benzoxazol-5-yl]-l-alanine methyl ester (BoxPhAnt) were studied in a series of solvents. Their absorption spectra are less sensitive to the solvent polarity than the corresponding fluorescence spectra which show a pronounced solvatochromic effect leading to large Stokes shifts. Using an efficient solvatochromic method, based on the empirical solvent polarity parameter , a large change of the dipole moment on excitation for BoxPhAnt has been found. From an analysis of the solvatochromic behaviour of the absorption and fluorescence spectra in terms of bulk solvent polarity functions, f(_r, n) and g(n), a larger excited-state dipole moment (about 8 D, ψ = 56) was obtained for BoxPhAnt than for BoxAnt (about 3 D, ψ = 0). Both applied methods gave similar values of the excited-state dipole moments for both compounds studied.     

Bischromophoric styrylpyridinium dyes. Spectroscopic properties of 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides

The photophysical properties of newly synthesized bischromophoric solvatochromic stilbazolium dyes, 1,3-bis-[4-(p-N,N-dialkylaminostyryl)pyridinyl]propane dibromides (C1-C9), were studied in a series of solvents and their spectroscopic properties were compared with structurally related, monochromophoric styrylpyridinium dyes (SP1-SP9). The position of the UV-vis absorption spectra maximum of novel dyes is only slightly solvent polarity dependent in contrast to the fluorescence spectra that show pronounced solvatochromic effect demonstrated by a large Stokes shifts. The influence of the solvent on absorption and emission spectra, and the solvatochromic properties observed for both ground and first excited states for all the dyes were used for the evaluation of their excited state dipole moments. The ground state dipole moments of both mono- and bischromophoric dyes were established by applying ab initio calculations. The calculations and measurements unexpectedly show that the bischromophoric dyes are characterized by ground state dipole moments being equal to about half of that characterizing their monomeric equivalents, while the excited state dipole moments of bischromophoric dyes are about 10-25% higher in comparison to their monomeric equivalents.     

Synthesis of new pyrido[2,3-d]pyrimidine derivatives

The mutual condensation of 4-aminouracil or 2,4-diamino-6-hydroxypyrimidine with bisacetonitrile and aldehydes was used to synthesize 2,4-dioxo-5-R-7-methyl-6-cyano-1,2,3,4,5,8-hexahydropyrido[2,3-d]pyrimidine and 2-amino-4-oxo-5-R-7-methyl-6-cyano-3,4,5,8-tetrahydropyrido[2,3-d]pyrimidine derivatives, which were oxidized with chromic anhydride to the corresponding 2,4-dioxo-5-R-7-inethyl-6-eyano-1,2,3,4-tetrahydropyrido[2,3-d]pyrimidine and 2-amino-4-oxo-5-R-7-methyl-6-cyano-3,4-dihydro[2,3-d]pyrimidines. The IR and UV spectra of the synthesized compounds were recorded.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 422–425, March, 1972.     

Electronic structures and spectroscopic properties of nitrido-osmium(VI) complexes with acetylide ligands [OsN(C[Triple Bond]CR)4]- R=H, CH3, and Ph by density functional theory calculation

Electronic structures and spectroscopic properties of a series of nitrido-osmium (VI) complex ions with acetylide ligands, [OsN(C[Triple Bond]CR)(4)](-) (R[Double Bond]H, (1), CH(3) (2), and Ph (3)) were investigated theoretically. The structures of the complexes were fully optimized at the B3LYP and CIS level for the ground states and excited states, respectively. The calculated bond lengths of Os[Triple Bond]N (1.639 A in 1, 1.642 A in 2, and 1.643 A in 3) and Os-C (2.040 A in 1, 2.043 A in 2, and 2.042 A in 3) in ground state agree well with the experimental results. The bond length of Os[Triple Bond]N bond is lengthened by ca. 0.13 A in the A (3)B(2) excited state compared to the (1)A(1) ground state, which is consistent with the lower vibration frequency of nu(Os-N) ( approximately 780 cm(-1)) in the excited state than that ( approximately 1175 cm(-1)) in the ground state. Among the calculated dipole-allowed absorptions at lambda>250 nm, the intense absorption at 261 nm for 1, 266 nm for 2, and 300 nm for 3 were attributed to the (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The lowest energy absorption at lambda(max)=393 nm for 1, 400 nm for 2, and 400 nm for 3 were assigned as (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], (1)[d(xy)(Os)+pi(C[Triple Bond]C)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C)], and (1)[d(xy)(Os)+pi(C[Triple Bond]CPh)]-->(1)[pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh)], respectively. The calculated phosphorescence emission at lambda(max)=581 nm for 1, 588 nm for 2, and 609 nm for 3 were originated from (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]C))(1)(d(xy)(Os)+pi(C[Triple Bond]C))(1)], and (3)[(pi(*)(N[Triple Bond]Os)+pi(*)(C[Triple Bond]CPh))(1)(d(xy)(Os)+pi(C[Triple Bond]CPh))(1)] excited state, respectively.     

Ion-dipole S(N)2 reaction in acetone-water mixtures. Electrostatic and specific solute-solvent interactions

The rate constants of the S(N)2 reaction of sodium 4-nitrophenoxide (1) and iodomethane were determined by UV-visible spectrophotometry in acetone-water mixtures at 25, 30, and 35 degrees C. The rate-Xwater (mole fraction of water) profile shows that the reaction depends strongly on the medium. The fastest rate constant was obtained in pure acetone, and a minimum occurred at Xwater= 0.4, whereas the observed second-order rate constants increases again in the water-rich region. In pure acetone, in the presence of dicyclohexano-[18]-crown-6, increases linearly with the concentration of the crown ether as a result of the complexation of the sodium ion (KS = 104.8 M) of the ion-pair and the increase in the effective concentration of free 4-nitrophenoxide ion, which was assumed to be the only reactive species. Ion-pairing was also detected at Xwater= 0.65 with a dissociation constant Kd = 7.82 x 10(-4) M(-1). The solvatochromic behaviors of 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-1-phenoxide (2), 4-[(1-methyl-4(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (3), and 1-methyl-8-oxy-quinolinium betaine (4) were investigated in the entire range of acetone-water mixtures. The dyes presented an increasing order of hydrophilicity compatible with their chemical structure, i.e., 2 < 3 < 4. Kinetic parameters for the methylation of 1 and the ET values of the dyes show a linear correlation of the polarity in the region of Xwater = 1.0-0.40 for 3 and 4, and it was observed that the more hydrophilic the dye the better the correlation coefficient, because of the structural similarity with 1. The activation parameter-Xwater profile shows extrema at Xwater < 0.4, reflecting an important change in the structure of the solvent that is responsible for the changes in the solvation of the reactive species including ion-pairs. These results suggest that the addition of water to acetone reduces abruptly the rate of substitution due to the preferential solvation (PS) of the phenoxide ion by the hydrogen-bonding donor (HBD) solvent. Nevertheless, the real second-order rate constant is "masked" by the association involving Na+ and 4-nitrophenoxide that extends even to water-rich mixtures. A model, based on the assumption that the free-energy terms involved in the second-order rate constant and the dissociation constant of the ion-pair have two components, is invoked to explain the kinetic data. One of the components depends on electrostatic interactions for which the main variable is the dielectric constant of the solvent mixture, and the other depends on the specific solute-solvent interactions, expressed by the activity coefficients of transfer of the species involved. The model indicates that in the range of Xwater = 1.0-0.40 the interactions are exclusively electrostatic, while for the rest of the acetone-rich region they are specific with a large contribution of the 4-nitrophenoxide ion.     

Surface interaction and self-assembly of cyclodextrins with organic dyes

The interaction of seven novel substituted merocyanine dyes, i.e. 1-methyl-4-[2-(3-methoxy-4-hydroxyphenyl)ethenyl)]pyridinium iodide, 1-methyl-4-[2-(3,5-dimethoxy-4-hydroxyphenyl)ethenyl)]pyridinium iodide, 1-methyl-4-[2-(4-dimethylaminophenyl)ethenyl)]pyridinium iodide, their quinoide forms as well as 1-methyl-4-[2-(3-methoxy-4-oxocyclohexadienilydene)ethylidene]-1,4-dihydropyridine, 1-methyl-4-[2-(3,5-dimethoxy-4-oxocyclohexadienilydene)ethylidene]-1,4-dihydropyridine, with α-CD, γ-CD as well as functionalized γ-cyclodextrin phosphate sodium salt is studied by the methods such as UV–Vis and fluorescence spectroscopy, linear-polarized infrared (IR-LD) spectroscopy of oriented colloids in nematic host, ¹H- and ¹³C-NMR spectroscopy, HPLC ESI tandem mass spectrometry, scanning electron and tunneling microscopy, powder X-ray diffraction as well as thermal methods. A formation of the 1D and 2D “supramolecular polymers” with nanosizes is found. The dyes are adsorbed on the CDs surface and form a hexagonal microcrystalline sub-structures. Remarkable fluorescence properties depending of the type of the substituent in the dyes, in solid-state are observed.     

Structural,photophysical, and electrophosphorescent properties of platinum(II) complexes supported by tetradentate N2O2 chelates

We present an examination of the structural and photophysical characteristics of [Pt(N(2)O(2))] complexes bearing bis(phenoxy)diimine auxiliaries (diimine=4,7-Ph(2)phen (1) and 4,4'-tBu(2)bpy (2)) that are tetradentate relatives of the quinolinolato (q) ligand. These neutral derivatives display high thermal stability (>400 degrees C in N(2)). While the crystal lattice in 1 consists of (head-to-tail)-interacting dimers, molecules of 2 are arranged into infinitely stacked planar sheets with possible pi-pi interactions but no close Pt.Pt contacts. Complexes 1 and 2 exhibit moderately intense low-energy UV/Vis absorptions around lambda=400-500 nm that undergo negative solvatochromic shifts. Both derivatives are highly luminescent in solution at 298 K with emission lifetimes in the micros range, and mixed (3)[l-->pi*(diimine)] (l=lone pair/phenoxide) and (3)[Pt(d)-->pi*(diimine)] charge-transfer states are tentatively assigned. The excited-state properties of 2 are also investigated by time-resolved absorption spectroscopy and by quenching experiments with pyridinium acceptors to estimate the excited-state redox potential. These emitters have been employed as electrophosphorescent dopants in multilayer OLEDs. Differences between the brightness, color, and overall performance of devices incorporating 1 and 2 are attributed to the influence of the diimine substituents.     

Indirect spectrophotometric determination of trace cyanide with cationic porphyrins

Three highly sensitive methods for the determination of cyanide have been developed, based on the fact that the complexation of silver ions with three cationic porphyrins, 5,10,15,20-tetrakis-(1-methyl-2-pyridinio)porphine [T(2-MPy)P], 5,10,15,20-tetrakis(1-methyl-3-pyridinio)porphine [T(3-MPy)P] and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphine [T(4-MPy)P], in alkaline media is inhibited by cyanide and the decrease in absorbance of the silver(II) complex is proportional to the cyanide concentration. Sensitivities of the procedures developed are 0.133, 0.126 and 0.234 ng/cm(2), respectively for an absorbance of 0.001. Cadmium(II), copper(II), mercury(II), zinc(II), iodide and sulfide interfere with the cyanide determination. One of the proposed methods was applied to the determination of cyanide in waste-water samples, with satisfactory results.