Nm In CH Research Articles

Synthesis, Structural Characterization, Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6-(7-Benzothiazol-2′-yl-9,9-diethyl-9 H-fluoren-2-yl)-2,2′-bipyridinyl Ligand

A platinum complex with the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridinyl ligand (1) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low-lying excited electronic states. Complex 1 exhibits intense structured (1)π-π* absorption at λ(abs)<440 nm, and a broad, moderate (1)MLCT/(1)LLCT transition at 440-520 nm in CH(2)Cl(2) solution. A structured (3)π-π*/(3)MLCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited-state absorption from 450 nm to 750 nm, which are tentatively attributed to the (1)π-π* and (3)π-π* excited states of the 6-(7-benzothiazol-2'-yl-9,9-diethyl-9H-fluoren-2-yl)-2,2'-bipyridine ligand, respectively. Z-scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near-IR wavelengths. The experimental data were fitted by a five-level model by using the excited-state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited-state absorption cross sections in the visible spectral region and the effective two-photon absorption cross sections in the near-IR region. Our results demonstrate that 1 possesses large ratios of excited-state absorption cross sections relative to that of the ground-state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH(2)Cl(2) solution illuminated by ns laser pulses at 532 nm. The two-photon absorption cross sections in the near-IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two-photon-assisted excited-state absorption in the near-IR region.

Synthesis and Photoelectrical Properties of Room-Temperature Phosphorescent (ppy)&lt;sub&gt;2&lt;/sub&gt;Ir(pybi) Complex

A blue-green emitter of iridium(III) complex (ppy) 2 Ir(pybi), has been synthesized (ppy= 2-phenyridine and pybi=2-(2-pyridyl)benzimdazole) and its structure was characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic resonance ( 1 H NMR), mass spectroscopy (MS), and elemental analysis. Its photophysical properties and energy-level structure were studied by UV-Vis absorption, excitation and emission spectroscopy, and cyclic voltammetry combining time- dependent density functional theory (TD-DFT). The electrophosphorescent performance of (ppy) 2 Ir(pybi) was characterized by using 4,4 -bis(9-carbazolyl)-1,1 -biphenyl (CBP) as host. The results indicated that the UV-Vis absorption bands were located at 250, 295, 346, and 442 nm, which were in good agreementwith the TD-DFT simulation results. The blue-green phosphorescent emission was observed with peaks at 495, 518 nm in CH 2 Cl 2 solution at room temperature. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels and optical gap were -6.11, -3.43, and 2.68 eV, respectively. Theoretical calculation revealed that the HOMO for (ppy) 2 Ir(pybi) was mainly distributed on the ppy ligand and the iridium ion, whereas the LUMO was centered mainly on the pybi ligand. The device based on the system of (ppy) 2 Ir(pybi) doped into CBP has an electroluminescence (EL) spectrum with a peak wavelength of 508 nm, a maximum luminance of 8451 cd · m -2 , and a maximum current efficiency of 17.6 cd · A -1 . These investigations will provide an important experimental basis for the application of (ppy) 2 Ir(pybi) in the organic electroluminescent field.

Fluorescent and Electrochemical Sensing of Polyphosphate Nucleotides by Ferrocene Functionalised with Two ZnII(TACN)(pyrene) Complexes

The [Fc-bis{Zn(II)(TACN)(Py)}] complex, comprising two Zn(II)(TACN) ligands (Fc=ferrocene; Py=pyrene; TACN=1,4,7-triazacyclononane) bearing fluorescent pyrene chromophores linked by an electrochemically active ferrocene molecule has been synthesised in high yield through a multistep procedure. In the absence of the polyphosphate guest molecules, very weak excimer emission was observed, indicating that the two pyrene-bearing Zn(II)(TACN) units are arranged in a trans-like configuration with respect to the ferrocene bridging unit. Binding of a variety of polyphosphate anionic guests (PPi and nucleotides di- and triphosphate) promotes the interaction between pyrene units and results in an enhancement in excimer emission. Investigations of phosphate binding by (31)P NMR spectroscopy, fluorescence and electrochemical techniques confirmed a 1:1 stoichiometry for the binding of PPi and nucleotide polyphosphate anions to the bis(Zn(II)(TACN)) moiety of [Fc-bis{Zn(II)(TACN)(Py)}] and indicated that binding induces a trans to cis configuration rearrangement of the bis(Zn(II)(TACN)) complexes that is responsible for the enhancement of the pyrene excimer emission. Pyrophosphate was concluded to have the strongest affinity to [Fc-bis{Zn(II)(TACN)(Py)}] among the anions tested based on a six-fold fluorescence enhancement and 0.1 V negative shift in the potential of the ferrocene/ferrocenium couple. The binding constant for a variety of polyphosphate anions was determined from the change in the intensity of pyrene excimer emission with polyphosphate concentration, measured at 475 nm in CH(3)CN/Tris-HCl (1:9) buffer solution (10.0 mM, pH 7.4). These measurements confirmed that pyrophosphate binds more strongly (K(b)=(4.45+/-0.41) x 10(6) M(-1)) than the other nucleotide di- and triphosphates (K(b)=1-50 x 10(5) M(-1)) tested.

A highly sensitive, selective, colorimetric and near-infrared fluorescent turn-on chemosensor for Cu2+ based on BODIPY

A new colorimetric and NIR fluorescent chemosensor (1) for Cu(2+) based on BODIPY is reported, displaying a highly sensitive and selective fluorescent enhancement with Cu(2+) among various metal ions, upon excitation at 620 nm in CH(3)CN.

Sensitive Valence Structures of [(pap)2Ru(Q)]n(n= +2, +1, 0, −1, −2) with Two Different Redox Noninnocent Ligands, Q = 3,5-Di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine and pap = 2-Phenylazopyridine

The complexes [(pap)(2)Ru(Q)]ClO(4), [1]ClO(4)-[4]ClO(4), with two different redox noninnocent ligands, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine (-aryl = m-(Cl)(2)C(6)H(3) (1(+)), C(6)H(5) (2(+)), m-(OCH(3))(2)C(6)H(3) (3(+)), and m-((t)Bu)(2)C(6)H(3) (4(+))) and pap = 2-phenylazopyridine, have been synthesized and characterized using various analytical techniques. The single-crystal X-ray structure of the representative [2]ClO(4).C(7)H(8) exhibits multiple intermolecular C-H...O hydrogen bondings and C-H...pi interactions. The C1-O1 = 1.287(4) (density functional theory, DFT, 1.311) and C6-N1 = 1.320(4) (DFT, 1.353) A and intraring bond distances associated with the sensitive quinine (Q) moiety along with the azo(pap) bond distances, N3-N4 = 1.278(4) (DFT, 1.297) and N6-N7 = 1.271(4) (DFT, 1.289) A, in 2(+) justify the [(pap)(2)Ru(II)(Q(*-))](+) valence configuration at the native state of 1(+)-4(+). Consequently, Mulliken spin densities on Q, pap, and Ru in 2(+) are calculated to be 0.8636, 0.1040, and 0.0187, respectively, and 1(+)-4(+) exhibit free radical sharp EPR spectra and one weak and broad transition around 1000 nm in CH(3)CN due to interligand transition involving a singly occupied molecular orbital (SOMO) of Q(*-) and the vacant pi* orbital of pap. Compounds 1(+)-4(+) undergo a quasi-reversible oxidation and three successive reductions. The valence structure of the electron paramagnetic resonance (EPR)-inactive oxidized state in 1(2+)-4(2+) has been established as [(pap)(2)Ru(II)(Q degrees )](2+) instead of the alternate formalism of antiferromagnetically coupled [(pap)(2)Ru(III)(Q(*-))](2+) on the basis of the DFT calculations on the optimized 2(+), which predict that the singly occupied molecular orbital is primarily composed of Q with 77% contribution. Accordingly, the optimized structure of 2(2+) predicts shorter C1-O1 (1.264) and C6-N1 (1.317 A) distances and longer Ru1-O1 (2.080) and Ru1-N1 (2.088 A) distances. Compounds 1(2+)-4(2+) exhibit the lowest energy transitions around 600 nm, corresponding to Ru(dpi)/Q(pi) --> pap(pi*). The presence of two sets of strongly pi-acceptor ligands, pap and Q, in 1(2+)-4(2+) stabilizes the Ru(II) state to a large extent such that the further oxidation of {Ru(II)-Q degrees } --> {Ru(III)-Q degrees } has not been detected within +2.0 V versus a saturated calomel electrode. The EPR-inactive reduced states 1-4 have been formulated as [(pap)(2)Ru(II)(Q(2-))] over the antiferromagnetically coupled alternate configuration, [(pap)(pap(*-))Ru(II)(Q(*-))]. The optimized structure of 2 predicts sensitive C1-O1 and C6-N1 bond distances of 1.337 and 1.390 A, respectively, close to the doubly reduced Q(2-) state, whereas the N horizontal lineN distances of pap, N3-N4 = 1.299 and N6-N7 = 1.306 A, remain close to the neutral state. In corroboration with the doubly reduced Q(2-) state, 1-4 exhibit a moderately strong interligand pi(Q(2-)) --> pi*(pap) transition in the near-IR region near 1300 nm. The subsequent two reductions are naturally centered around the azo functions of the pap ligands.

Synthesis, glycosylation and photolysis of photolabile 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC) protected glycopyranosides

The photolabile NPPOC group has been successfully introduced into the 6-position of various glycopyranosides in 91-97% yield. Glycosylation of NPPOC-protected phenyl beta-D-thiogluco- and galactopyranosides with appropriate acceptors afforded the corresponding disaccharides in good yield. Excellent beta-stereoselectivity (beta/alpha>or= 10/1) can be obtained when the glycosylation was realized in CH(3)CN at -40 degrees C. Furthermore, the 6-O-NPPOC thioglucoside can also be readily converted into the corresponding glucopyranose or glucosyl fluoride. The photolysis of 6-O-NPPOC diacetone D-galactose has been studied by UV-vis absorption in CH(3)CN in the presence of water or DBU at 365 nm. At 100 microM concentration, photocleavage of was accomplished after 5 min irradiation, with t(1/2) = 37 s (10% water), 75 s (1 equiv. DBU) or 87 s (0.05 M DBU). The formation of the nitroso byproduct can be avoided in the presence of 0.05 M DBU. All the NPPOC-protected mono- or disaccharides can be readily removed by photolysis at 365 nm in CH(3)CN the presence of water or DBU in more than 87% yield.

Dual Excited-State Intramolecular Proton Transfer Reaction in 3-Hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

The synthesis, characterization and fundamental of the dual excited-state proton-transfer properties of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a) are reported. In the electronic ground state, there exist two competitive hydrogen bonding (HB) isomers for 1a. Conformer 1a(O) reveals a five-membered ring HB structure between O-H and carbonyl oxygen, while conformer 1a(N) possesses a six-membered ring HB formation between O-H and pyridyl nitrogen. In a single crystal, the X-ray crystallography unveils an exclusive formation of conformer 1a(N). In solution such as CH(2)Cl(2), 1a(O) and 1a(N) are in equilibrium, and their respective absorption chromophores are significantly different due to different degrees of hydrogen-bond induced pi electron delocalization. Upon excitation, both conformers 1a(O) and 1a(N) undergo excited-state intramolecular proton transfer (ESIPT) reaction. Following ESIPT, 1a(O) gives rise to a tautomer emission maximized at 534 nm in CH(2)Cl(2). Conversely, due to dominant radiationless quenching processes the tautomer emission for 1a(N) cannot be obtained with a steady-state manner but can be resolved from time-resolved fluorescence. Time resolved fluorescence estimates an equilibrium constant of 27 +/- 5 in favor of 1a(N) in CH(2)Cl(2). Ultrafast ESIPT also takes place for the unique 1a(N) form in the crystal. Due to the prohibition of quenching processes in the solid state, bright tautomer emission maximized at 540 nm is resolved for 1a(N) (Phi(f) approximately 0.3). The interplay between two HB conformers with on(1a(O))/off(1a(N)) character in tautomer emission may find future applications such as the recognition of organic Lewis acid/base in organic solvents.

Electrochemical and Spectroscopic Characterization of a Series of Mixed-Ligand Diruthenium Compounds

The electrochemistry and spectroelectrochemistry of a novel series of mixed-ligand diruthenium compounds were examined. The investigated compounds having the formula Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl where x = 1-3 and Fap is 2-(2-fluoroanilino)pyridinate anion were made from the reaction of Ru(2)(CH(3)CO(2))(4)Cl with 2-(2-fluoroanilino)pyridine (HFap) in refluxing methanol. The previously characterized Ru(2)(Fap)(4)Cl as well as the three newly isolated compounds represented as Ru(2)(CH(3)CO(2))(Fap)(3)Cl (1), Ru(2)(CH(3)CO(2))(2)(Fap)(2)Cl (2), and Ru(2)(CH(3)CO(2))(3)(Fap)Cl (3) possess three unpaired electrons with a Ru(2)(5+) dimetal core. Complexes 1 and 2 have well-defined Ru(2)(5+/4+) and Ru(2)(5+/6+) redox couples in CH(2)Cl(2), but 3 exhibits a more complicated electrochemical behavior due to equilibria involving association or dissociation of the anionic chloride axial ligand on the initial and oxidized or reduced forms of the compound. The E(1/2) values for the Ru(2)(5+/4+) and Ru(2)(5+/6+) processes vary linearly with the number of CH(3)CO(2)(-) bridging ligands on Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl and plots of reversible half-wave potentials vs the number of acetate groups follow linear free energy relationships with the largest substituent effect being observed for the oxidation. The major UV-visible band of the examined compounds in their neutral Ru(2)(5+) form is located between 550 and 800 nm in CH(2)Cl(2) and also varies linearly with the number of CH(3)CO(2)(-) ligands on Ru(2)(CH(3)CO(2))(x)(Fap)(4-x)Cl. The electronic spectra of the singly oxidized and singly reduced forms of each diruthenium species were characterized by UV-visible spectroelectrochemistry in CH(2)Cl(2).

Characterization of Reactive Intermediates Generated During Photolysis of 4-Acetoxy-4-aryl-2,5-cyclohexadienones: Oxenium Ions and Aryloxy Radicals

Aryloxenium ions 1 are reactive intermediates that are isoelectronic with the better known arylcarbenium and arylnitrenium ions. They are proposed to be involved in synthetically and industrially useful oxidation reactions of phenols. However, mechanistic studies of these intermediates are limited. Until recently, the lifetimes of these intermediates in solution and their reactivity patterns were unknown. Previously, the quinol esters 2 have been used to generate 1, which were indirectly detected by azide ion trapping to generate azide adducts 4 at the expense of quinols 3, during hydrolysis reactions in the dark. Laser flash photolysis (LFP) of 2b in the presence of O(2) in aqueous solution leads to two reactive intermediates with lambda(max) 360 and 460 nm, respectively, while in pure CH(3)CN only one species with lambda(max) 350 nm is produced. The intermediate with lambda(max) 460 nm was previously identified as 1b based on direct observation of its decomposition kinetics in the presence of N(3)(-), comparison to azide ion trapping results from the hydrolysis reactions, and photolysis reaction products (3b). The agreement between the calculated (B3LYP/6-31G(d)) and observed time-resolved resonance Raman (TR(3)) spectra of 1b further confirms its identity. The second intermediate with lambda(max) 360 nm (350 nm in CH(3)CN) has been characterized as the radical 5b, based on its photolytic generation in the less polar CH(3)CN and on isolated photolysis reaction products (6b and 7b). Only the radical intermediate 5b is generated by photolysis in CH(3)CN, so its UV-vis spectrum, reaction products, and decay kinetics can be investigated in this solvent without interference from 1b. In addition, the radical 5a was generated by LFP of 2a and was identified by comparison to a published UV-vis spectrum of authentic 5a obtained under similar conditions. The similarity of the UV-vis spectra of 5a and 5b, their reaction products, and the kinetics of their decay confirm the assigned structures. The lifetime of 1b in aqueous solution at room temperature is 170 ns. This intermediate decays with first-order kinetics. The radical intermediate 5b decomposes in a biphasic manner, with lifetimes of 12 and 75 mus. The decay processes of 5a and 5b were successfully modeled with a kinetic scheme that included reversible formation of a dimer. The scheme is similar to the kinetic models applied to describe the decay of other aryloxy radicals.

Selective Fluorimetric Recognition of Cesium Ion by 15-Crown-5-Anthracene

A selective fluorescent cesium optode on a chromoionophore consisting of anthracene covalently linked through an imine bond to a 15-crown-5 derivative has been reported. In the present system, 15-crown-5 derivative including anthracene was used a fluoroionophore. The fluorescence response mechanism is based on the photo-induced electron transfer (PET) from the lone pair of electrons of the nitrogen to the anthracene group and inhibition of PET system by cesium binding while increasing the fluorescence intensity. Emission intensity 15-crown-5 anthracene was measured at 500 nm with absorbance at 400 nm in CH(3)CN-H(2)O (1:1) media. The method shows a very good selectivity and sensitivity for cesium with respect to other cations such as K(+), Na(+) and Li(+) with linear range and detection limit of 5.0 x 10(-5) to 5.0 x 10(-1)M and 3.0 x 10(-6)M respectively.

A flexible 1,8-naphthyridyl derivative and its Zn(II) complexes: synthesis, structures, spectroscopic properties and recognition of Cd(II)

A flexible ligand bis(7-methyl-1,8-naphthyridine-2-ylamino)methane (), having kappa(4)-chelating and kappa(2)-bridging modes, and its intriguing structural complexes of Zn(II) with mu-OH, kappa(1)-OAc, mu-kappa(1)-OAc and mu-kappa(2)-OAc ligands, [Zn(2)()(2)(OH)](ClO(4))(3) (), [Zn(4)()(2)(OAc)(6)(OH)(2)].CH(2)Cl(2) (.CH(2)Cl(2)) and [Zn(5)()(2)(OAc)(10)](n).4nH(2)O (.4H(2)O) were synthesized and their structures were determined by X-ray crystallography. These compounds exhibited intense blue fluorescent emissions with a lambda(max) in the range of 380-410 nm in CH(2)Cl(2), CH(3)CN and CH(3)OH solutions, and solid-state emissions centered at 416, 463, 490 and 451 nm were observed for the compounds , , and at room temperature, respectively. The investigated fluorescence properties of associated with various metal ions showed that the fluorescence enhancement of with Cd(II) was more sensitive than with other interfering cations.

X-Shaped Electro-optic Chromophore with Remarkably Blue-Shifted Optical Absorption. Synthesis, Characterization, Linear/Nonlinear Optical Properties, Self-Assembly, and Thin Film Microstructural Characteristics

A novel type of "X-shaped" two-dimensional electro-optic (EO) chromophore with extended conjugation has been synthesized and characterized. This chromophore is found to exhibit a remarkably blue-shifted optical maximum (357 nm in CH(2)Cl(2)) while maintaining a very large first hyperpolarizability (beta). Hyper-Rayleigh Scattering (HRS) measurements at 800 nm provide a beta(zzz) value of 1840 x 10(-30) esu. Self-assembled thin films of this chromophore were fabricated via a layer-by-layer chemisorptive siloxane-based approach. The chromophoric multilayers have been characterized by transmission optical spectroscopy, advancing contact angle measurements, synchrotron X-ray reflectivity, atomic force microscopy, and angle-dependent polarized second harmonic generation spectroscopy. The self-assembled chromophoric films exhibit a dramatically blue-shifted optical maximum (325 nm) while maintaining a large EO response (chi(2)(333) approximately 232 pm/V at 1064 nm; r(33) approximately 45 pm/V at 1310 nm). This work demonstrates an attractive approach to developing EO materials offering improved nonlinearity-transparency trade-offs.

Controlling Emission Energy, Self-Quenching, and Excimer Formation in Highly Luminescent N∧C∧N-Coordinated Platinum(II) Complexes

A series of cyclometalated platinum(II) complexes have been prepared, [PtL(n)Cl], containing N--C--N-coordinating, terdentate ligands based on 1,3-dipyridylbenzene (HL(1)), incorporating aryl substituents at the central 5 position of the ligand. All of the new complexes are intensely luminescent in a degassed solution at 298 K (phi = 0.46-0.65 in CH(2)Cl(2)) with lifetimes in the microsecond range (7.9-20.5 micros). The introduction of the aryl substituents leads to a red shift in the lowest-energy, intense charge-transfer absorption band compared to [PtL(1)Cl] (401 nm in CH(2)Cl(2)), in the order H < mesityl < 2-pyridyl < 4-tolyl < 4-biphenylyl < 2-thienyl < 4-(dimethylamino)phenyl (431 nm in CH(2)Cl(2)), which correlates with the decreasing order of oxidation potentials. A similar order is also observed in the emission maxima, ranging from 491 nm for [PtL(1)Cl] to 588 nm for the 4-(dimethylamino)phenyl-substituted complex. The emission spectra of all of the complexes, except for the amino-substituted compound, are highly structured in a dilute solution in CH(2)Cl(2), and the emission is assigned to excited states of primarily (3)LC (ligand-centered) character. At higher concentrations, self-quenching accompanied by structureless excimer emission centered at 700 nm is observed, but the aryl groups attenuate the self-quenching compared to the parent compound [PtL(1)Cl], particularly for the most sterically hindered mesityl complex. The introduction of the strongly electron-donating 4-dimethylamino substituent leads to a switch in the nature of the lowest-energy excited state from (3)LC to one of primarily intraligand charge-transfer (ILCT) character in CH(2)Cl(2): this complex displays a structureless and much broader emission band than the other compounds and a high degree of positive solvatochromism. No excimer emission is observed in CH(2)Cl(2), and self-quenching is an order of magnitude lower than that for the other complexes. However, in nonpolar solvents such as CCl(4), the ILCT state is destabilized, such that the (3)LC remains the lowest-energy excited state. Reversible switching between the ILCT and (3)LC states can also be achieved in a CH(2)Cl(2) solution by protonation of the amine, with an accompanying large change in the emission maxima of >100 nm. The X-ray structures of the biphenylyl- and methyl-substituted complexes are reported, together with those of the 2-pyridyl- and mesityl-substituted ligands and the key synthetic intermediate 1-bromo-3,5-di(2-pyridyl)benzene.

Anthracene-9-methanol—a novel fluorescent phototrigger for biomolecular caging

Photoexcitation of a solution of anthracene-9-methanol derived esters at ∼386 nm in CH 3CN/H 2O (3:2 v/v) results in fluorescence emission in the 380–480 nm range, with quantum yields of fluorescence ( Φ f ) in the 0.01–0.09 range and releases of the carboxylic acids in good chemical yields (43–100%), with quantum yields of photoreaction ( Φ PR, i.e., the photodisappearance of the esters) in the 0.067–0.426 range.

The Phane Properties ofanti-[2.2](1,4)Biphenylenophane

[structure: see text] Anti-[2.2](1,4)biphenylenophane (4) was synthesized from de Meijere's tetrabromo[2.2]paracyclophane (5) through a four-step reaction sequence. Although an average separation of 3.09 A between the inner ring of the biphenylene units is normal for [2.2]paracyclophanes, a bond distance of 1.54 Afor the ethano C-C bridge at room temperature is shorter than usual. In addition, trimethylsilyl-substituted anti-[2.2](1,4)biphenylenophane 8 sublimes at 220 degrees C under a pressure lower than 1 x10(-5) Torr without decomposition or thermal isomerization. The high thermal stability of 8 suggested that the ethano bridges of the biphenylenophanes are less strained than those of [2.2]paracyclophane. Bathochromic shifts are observed in their UV-vis absorption spectra. The phane state interactions of 4 and 8 were evidenced by the weak structureless fluorescent emission maximized at 537 and 550 nm in CH(2)Cl(2) along with longer relaxation lifetimes of 229 and 292 ps, respectively.

Fluorescent and circular dichroic detection of monosaccharides by molecular sensors: bis[(pyrrolyl)ethynyl]naphthyridine and bis[(indolyl)ethynyl]naphthyridine.

The push-pull conjugated molecules 2,7-bis-(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN) and 2,7-bis(1H-indol-2-yl)ethynyl-1,8-naphthyridine (BIN) adopting daad relays of proton donors (d) and acceptors (a) form multiple hydrogen-bonding complexes with various monosaccharides that possess complementary adda sequences. Although the free BPN emits blue light at lambda(max) = 475 nm in CH(2)Cl(2), its complexation with octyl beta-d-glucopyranoside gives green fluorescence at lambda(max) = 535 nm. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM. On the other hand, the CD-silent BIN molecule binds with monosaccharides to form the CD-active multiple hydrogen-bonding complexes, which exhibit the remarkable chirality dependent helicities consistent with the prediction by the ab initio approaches. On the basis of the similar daad cleft and hence the binding property, the fluorescence and CD absorption methods in BPN and BIN, respectively, are complementary, which, in combination with computational molecular modeling, not only give a detailed insight into the structures of the receptor-saccharide complexes in solution, but also differentiate octyl beta-d-glucopyranoside from its enantiomer and other monosaccharides.

Polymorphic forms of a gold(I) arylacetylide complex with contrasting phosphorescent characteristics.

The spectroscopic properties and crystal structures of the gold(I) arylacetylide complexes [(R(3)P)Au(Ctbd1;CAr)] (R = Cy, Ar = 4-nitrophenyl, 1; 4-trifluoromethylphenyl, 2; pentafluorophenyl, 3; R = Ph, Ar = 4-nitrophenyl, 4) have been examined. The dipole-allowed and -forbidden transitions of 1 (4 in parentheses) at lambda(max) 340 (336) and ca. 485 (470) nm in CH(2)Cl(2) solution at 298 K are assigned to the singlet and triplet intraligand charge transfer (ILCT) transitions of the 4-nitrophenylacetylide moiety, whereas 2 (3 in parentheses) shows localized singlet and triplet acetylenic pipi transitions at lambda(max) 287 (276) and 426 nm, respectively. Two polymorphs of 1 with contrasting phosphorescent characteristics have been identified. At 298 K, the emissive form of 1, as well as 2-4, are highly phosphorescent with peak maximum at 504, 425, 521, and 495 nm, respectively; the other polymorph of 1 is nonemissive at 298 K but emission is detected at 77 K with peak maximum at 486 nm. Crystallographic studies reveal that the major differences between the emissive and nonemissive forms of 1 are the orientations of the molecular dipoles and the dihedral angles between neighboring 4-nitrophenyl moieties. Crystal 2 is isostructural to the nonemissive form of 1, but does not display polymorphism. The molecular planes of two neighboring lumophores are coplanar in the emissive form of 1, parallel in 4, and nearly perpendicular (78.6 degrees ) to each other in the nonemissive form of 1. Both the nature of the excited state and the dihedral angle between adjacent [Au(Ctbd1;CAr)] moieties determine the phosphorescent properties of these molecular crystals.

A Luminescent Supermolecule with Gold(I) Quinoline-8-thiolate: Crystal Structure, Spectroscopic and Photophysical Properties

The trinuclear complex [(8-QNS)(2)Au(AuPPh(3))(2)].BF(4) (8-QNS = quinoline-8-thiolate), with intramolecular gold(I)...gold(I) distances of 3.0952(4) and 3.0526(3) A, is aggregated to form a novel hexanuclear supermolecule, ([(8-QNS)2(Au(AuPPh3)2])2.(BF4)2, via a close intermolecular gold(I)...gold(I) contact of 3.1135(3) A. The beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it emits at ca. 440 and 636 nm in CH(2)Cl(2) and only at ca. 450 nm in CH(3)CN. The long-lived emission at ca. 636 nm (16.2 micros) in CH(2)Cl(2) is quenched by polar solvents such as CH(3)CN and CH(3)OH with quenching constants as 1.00 x 10(5) and 3.03 x 10(4) s(-1) M(-1), respectively, which is suggested to be related to the presence or absence of gold(I)...gold(I) interactions due to scrambling of the [AuPPh(3)]+ units, isolobal to H+.

Ethyl 2-[[2-(3-nitrophenyl)-5-phenyl-1H-imidazol-4-yl]sulfanyl]acetate: synthesis via a microwave-mediated combinatorial chemistry approach.

The orange title compound, C(19)H(17)N(3)O(4)S, can be synthesized either via microwave-mediated combinatorial chemistry strategies or conventional synthetic procedures. The phenyl and meta-nitrophenyl C(6) rings are essentially coplanar with the central imidazolyl ring, with interplanar angles of 0.87 (5) and 0.97 (4), respectively, resulting in optimum conjugation (SCH(2) moiety included); lambda(max) = 281 nm in CH(3)CN. The principal intermolecular interactions are N(imid)-H...O(nitro) and N(imid)-H...O[double bond]C [N...O = 3.058 (2) and 3.432 (3) A, and N-H...O = 128 and 153, respectively]. The closest H.S distance is an intramolecular C-H...S contact, with H...S = 2.54 A and C-H...S = 136.

Syntheses and Structural Characterization of Luminescent Platinum(II) Complexes Containing Di-tert-butylbipyridine and New 1,1-Dithiolate Ligands

Three new di-tert-butylbipyridine (dbbpy) complexes of platinum(II) (1-3) containing 1,1-dithiolate ligands have been synthesized and characterized. The 1,1-dithiolates are 2,2-diacetylethylene-1,1-dithiolate (S(2)C=C(C(O)Me)2) (1), 2-cyano-2-p-bromophenylethylene-1,1-dithiolate (S(2)C=C(CN)(p-C(6)H(4)Br)) (2), and p-bromophenyl-2-cyano-3,3-dithiolatoacrylate (S(2)C=C(CN)(COO-p-C(6)H(4)Br)) (3). Complex 1 exhibits a solvatochromic charge-transfer absorption in the 430-488 nm region of the spectrum and a luminescence around 635 nm in ambient temperature CH(2)Cl(2) solution. These observations are consistent with what has been seen previously in related Pt diimine 1,1-dithiolate complexes. The nature of the emissive state is assigned as a (3)(mixed metal/dithiolate-to-diimine) charge transfer, while the solvatochromic absorption band corresponds to the singlet transition of similar orbital character. The other complexes also exhibit a low-energy solvatochromic absorption. The crystal structures of two of the complexes have been determined, representing the first time that Pt(diimine)(1,1-dithiolate) complexes have been crystallographically studied. The structures confirm the expected square planar coordination geometry with distortions in bond angles dictated by the constraints of the chelating ligands. The Pt-S and Pt-N bond lengths and S-Pt-S and N-Pt-N bond angles for the two structures are identical within experimental error (2.283(2) and 2.278(2) A; 2.053(6) and 2.050(8) A; 75.01(8) degrees and 75.40(8) degrees; 79.2(2) degrees and 79.0(2) degrees, respectively). Crystal data for 1: monoclinic, space group P2(1)/n (No. 14), with a = 7.20480(10) A, b = 20.53880(10) A, c = 19.1072(2) A, beta = 93.83 degrees, V = A(3), Z = 4, R1 = 3.34% (I > 2sigma(I)), wR2 = 9.88% (I > 2sigma(I)) for 3922 unique reflections. Crystal data for 2: monoclinic, space group P2(1)/n (No. 14), with a = 15.0940(5) A, b = 9.5182(3) A, c = 20.4772(7) A, beta = 111.151(1) degrees, V = A(3), Z = 4, R1 = 4.07% (I > 2sigma(I)), wR2 = 8.64% (I > 2sigma(I)) for 3859 unique reflections.