Absorption spectra, photophysical properties, and redox behavior of ruthenium(II) polypyridine complexes containing accessory dipyrromethene-BF2 chromophores

The six multichromophoric species 1-6, containing the potentially luminescent Ru(II) polypyridine subunits and 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene fluorophores (dipyrromethene-BF(2) dyes, herein after called bodipy), have been prepared and their absorption spectra, luminescence properties (both at room temperature in fluid solution and at 77 K in rigid matrix), and redox properties have been investigated (for the structuralformulas of all the compounds, see Figure 1). For comparison purposes, also the same properties of the bodipy-based free ligands have been examined. Three of the multichromophoric species (1-3) are based on the Ru(bpy)(3)-type metal subunit, whereas 4-6 are based on the Ru(terpy)(2)-type metal subunit. Transient absorption spectroscopy at room temperature of all the compounds has also been performed. The absorption spectra of all the metal complexes show features that can be assigned to the Ru(II) polypyridine subunits and to the bodipy centers. In particular, the lowest energy spin-allowed pi-pi* transition of the bodipy groups dominates the visible region, peaking at about 530 nm. All the new complexes exhibit a rich redox behavior, with reversible processes attributed to specific sites, indicating a small perturbation of each redox center and therefore highlighting the supramolecular nature of the multichromophoric assemblies. Despite the good luminescence properties of the separated components, 1-6 do not exhibit any luminescence at room temperature; however, transient absorption spectroscopy evidences that for all of them a long-lived (microsecond time scale) excited state is formed, which is identified as the bodipy-based triplet state. Pump-probe transient absorption spectroscopy suggests that such a triplet state is formed from the promptly prepared bodipy-based (1)pi-pi* state in most cases by the intervention of a charge-separated level. At 77 K, all the complexes except complex 1 exhibit the bodipy-based fluorescence, although with a slightly shortened lifetime compared to the corresponding free ligand(s), and 4-6 also exhibit a phosphorescence assigned to the bodipy subunits. Phosphorescence of bodipy species had never been reported in the literature to the best of our knowledge: in the present cases we propose that it is an effective decay process thanks to the presence of the ruthenium heavy atom and of the closely lying (3)MLCT state of the Ru(terpy)(2)-type subunits.     

Photoinduced intercomponent processes in multichromophoric species made of Pt(II)-terpyridine-acetylide and dipyrromethene-BF2 subunits

A new multicomponent species made of Pt(II) terpyridine and difluoroborondipyrromethene (bodipy) dyes is synthesized and its absorption, redox, and emission properties are reported; photoinduced energy transfer from the Pt-based (3)MLCT state to the bodipy triplet occurs both at room temperature and at 77 K.     

Investigation of the zinc(II)-benzoate-2-pyridinealdoxime reaction system

The employment of pyridine-2-carbaldehyde oxime (paoH) in zinc(II) benzoate chemistry, in the absence or presence of azide ions, is described. The syntheses, crystal structures and spectroscopic characterization are reported for the complexes [Zn(O(2)CPh)(2)(paoH)(2)] (1), [Zn(12)(OH)(4)(O(2)CPh)(16)(pao)(4)] (2) and [Zn(4)(OH)(2)(pao)(4)(N(3))(2)] (3). The Zn(II) centre in octahedral 1 is coordinated by two monodentate PhCO(2)(-) groups and two N,N'-chelating paoH ligands. The metallic skeleton of 2 describes a tetrahedron encapsulated in a distorted cube. The {Zn(12)(μ-OH)(4)(μ(3)-ΟR)(4)}(16+) core of the cluster can be conveniently described as consisting of a central {Zn(4)(μ(3)-ΟR)(4)}(4+) cubane subunit (RO(-) = pao(-)) linked to four {Zn(2)(μ-OH)}(3+) subunits via the OH(-) group of each of the latter, which becomes μ(3). The molecule of 3 has an inverse 12-metallacrown-4 topology. Two triply bridging hydroxido groups are accommodated into the metallacrown ring. Each pao(-) ligand adopts the η(1)?:?η(1)?:?η(1)?:?μ coordination mode, chelating one Zn(II) atom and bridging a Zn(II)(2) pair. Complexes 1 and 2 display photoluminescence with maxima at ～355 nm and ～375 nm, upon maximum excitation at 314 nm; the origin of the photoluminescence is discussed.     

Sensitized near-IR luminescence of Ln(III) complexes with benzothiazole derivatives

Lanthanide complexes with benzothiazole derivatives (Btz-R, R = OCH(3) and OH) and terpyridine (tpy) ligands were synthesized, and their photophysical properties were precisely investigated. The free Btz-OCH(3) ligand in toluene, excited with UV light, produced the normal emission bands around 410 nm, whereas Btz-OH produced a strong excited-state intramolecular proton transfer (ESIPT) band at 510 nm. The Ln(III) complexes (Ln = Nd, Er, and Yb) exhibited sensitized near-IR luminescence when the Btz-R ligands were excited. The sensitized luminescence quantum yields (Phi(Ln)) of the lanthanide complexes were markedly enhanced by ESIPT: for [Nd(Btz-R)(tpy)] in toluene solution, Phi(Ln) = 0.04% for Btz-OCH(3) and 0.39% for Btz-OH. The sensitized luminescence of the Er(III) complexes (Phi(Ln) = 0.002% for Btz-OCH(3) and 0.009% for Btz-OH) was less efficient than that of the Nd(III) complexes. This difference is due to the smaller energy gap between the emitting and ground levels of the Er(III) ion. The rate constants for the energy transfer from Btz-R to Ln(III) were about approximately 10(9) s(-1), as evaluated by the F?rster resonance energy transfer mechanism.     

A minimalist approach to understanding the efficiency of mononuclear Zn(II) complexes as catalysts of cleavage of an RNA analog

Mononuclear complexes between Zn(2+) and the following four macrocycles were prepared: 1,4,7,10-tetraazacyclododecane (1), 1-oxa-4,7,10-triazacyclododecane (2), 1,5,9-triazacyclododecane (3) and 1-hydroxyethyl-1,4,7-triazacyclononane (4). The pH rate profiles of values of the observed second-order rate constant log (k(Zn))(app) for Zn(X)(OH(2))-catalyzed cleavage (X = 1, 2, 3 and 4) of 2-hydroxypropyl-4-nitrophenyl phosphate (HpPNP) show downward breaks centered at the pK(a) for ionization of the respective zinc bound water. At low pH, where the rate acceleration for the catalyzed reaction is largest, the stabilizing interaction between the catalyst and the bound transition state is 5.7, 7.4, 7.4 and 5.9 kcal mol(-1) for the reactions catalyzed by Zn(1)(OH(2)), Zn(2)(OH(2)), Zn(3)(OH(2)) and Zn(4)(OH(2)), respectively. The interactions between the metal cation and the macrocycle cause either a modest increase or reduction in transition state stabilization compared with 6.6 kcal mol(-1) stabilization for catalysis by Zn(OH(2))(6). The best Zn(II)-macrocycle catalysts are those for which the interactions between the metal ion and macrocycle are the weakest. Inhibition studies show that each of the four catalysts form complexes with phosphate and oxalate dianions with a much higher affinity than diethyl phosphate monoanion, consistent with stronger interaction of the catalysts with the transition state dianion compared with the substrate monoanion HpPNP. The pH-dependence of methyl phosphate inhibition of Zn(2) catalyzed cleavage of HpPNP shows that only the Zn(2)(OH(2)) species binds the inhibitor. This result is consistent with a mechanism that has Zn(2)(OH(2)) as the active catalytic species.     

Caging effects on the ground and excited states of 2,2'-bipyridine-3,3'-diol embedded in cyclodextrins

The 2,2'-bipyridine-3,3'-diol (BP(OH)(2)) molecule shows unique spectroscopic features in water that may position it as a new biological probe. In an attempt to mimic biological environments, we explore in this paper the caging effects of cyclodextrins on the steady state spectra of BP(OH)(2). The caging effects of gamma-, beta-, and 2,6-di-O-methyl-beta-cyclodextrins (CDs) on the ground and excited state properties of BP(OH)(2) in aqueous solutions are investigated by steady state absorption and fluorescence spectroscopy, and by ab initio calculations. The stoichiometry of the three complexes was found to be 1:1 and the binding constants were estimated from the absorption and fluorescence spectra. In the case of gamma-CD, the large cavity size supports only small binding, whereas such binding increases in the cases of the smaller cavity sizes of beta-CD and 2,6-di-O-methyl-beta-CD. Maximum binding was measured in the case of 2,6-di-O-methyl-beta-CD due to the increased hydrophobicity of the host cavity. The unique absorption features of BP(OH)(2) in water show a dramatic decrease in intensity due to caging effects. The decrease in intensity correlates very well with the extent of binding and hydrophobicity of the host molecules. Similar results were also obtained from the fluorescence spectra. The calculated structure of the BP(OH)(2):beta-CD complex predicts that the inclusion of BP(OH)(2) is nearly axial and centered inside the beta-CD cavity. The BP(OH)(2) molecule maintains its dienol moiety in the complex with no possible hydrogen bonding with the host interior H-atoms. The results are discussed in light of the possible use of BP(OH)(2) as a water sensor in biological systems.     

Study of the Photochemical Properties and Conical Intersections of [2,2′‐Bipyridyl]‐3‐amine‐3′‐ol

The two isoelectronic bipyridyl derivatives [2,2′‐bipyridyl]‐3,3′‐diamine and [2,2′‐bipyridyl]‐3,3′‐diol are experimentally known to undergo very different excited‐state double‐proton‐transfer processes, which result in fluorescence quantum yields that differ by four orders of magnitude. In a previous study, these differences were explained from a theoretical point of view, because of topographical features in the potential energy surface and the presence of conical intersections (CIs). Here, we analyze the photochemical properties of a new molecule, [2,2′‐bipyridyl]‐3‐amine‐3′‐ol [BP(OH)(NH₂)], which is, in fact, a hybrid of the former two. Our density functional theory (DFT), time‐dependent DFT (TDDFT), and complete active space self‐consistent field (CASSCF) calculations indicate that the double‐proton‐transfer process in the ground and first singlet π→π* excited state in BP(OH)(NH₂) presents features that are between those of their “parents”. The presence of two CIs and the role they may play in the actual photochemistry of BP(OH)(NH₂) and other bipyridyl derivatives are also discussed.     

Sensitive and selective PET-based diimidazole luminophore for Zn(II) ions: a structure-activity correlation

3-(3-Ethoxymethyl-1H-imidazol-2-yl)-3-(1-ethoxymethyl-1H-imidazol-2-yl)-3H-benzo[de]isochromen-1-one, 4, is a novel photoinduced electron transfer (PET) chemosensor that becomes fluorescent upon binding metal ions and shows a strong preference toward Zn(II) ions. The new bisimidazol PET sensor and its zinc complex were prepared and characterized in terms of their crystal structures, absorption and emission spectra, and orbital energy diagrams. Free 4 is a weakly luminescent species. On the basis of detailed DFT calculations, we suggest that the poor luminescence yield of free 4 originates from its orbital structure in which two pi-orbitals of the two imidazole rings, HOMO and HOMO-1, are situated between two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO. The absorption and emission processes occur between the two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO, and the two pi-imidazole orbitals serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding Zn(II) ions, 4 becomes a highly luminescent species having a luminescence maximum peaking at 375 nm (lambda(ex) = 329 nm). The significant 900-fold enhancement in luminescence upon binding of the Zn(II) ions is attributed to the stabilization of the pi-orbitals of the imidazole rings upon their engagement in new bonds with the zinc ion. The affinity of 4 to zinc ions in acetonitrile is found to be very high, Ka > 3 x 10(6) M(-1), while with other metals ions, the association constants are considerably weaker.     

Blue phosphorescent Zn(II) and orange phosphorescent Pt(II) complexes of 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyrimidine

To investigate the different phosphorescent promoting effects of organic emitters by various metal centers, a new ligand, 4,4'-diphenyl-6,6'-dimethyl-2,2'-bipyrimidine (pmbp), and its Zn(II), Hg(II), and Pt(II) complexes, [Zn(pmbp)(2)](ClO(4))(2)(1), Pt(pmbp)Ph(2)(2), Zn(pmbp)Cl(2)(3), and Hg(pmbp)Cl(2)(4) were synthesized. Their structures were determined by single crystal X-ray diffraction. The zinc complexes 1 and 3 exhibit blue luminescence in the solid state at ambient temperature, but the mercury complex 4 is not luminescent. At 77 K, both pmbp and complex have blue emissions in MeOH solutions, which were demonstrated to be phosphorescence by their long decay lifetime (micros). By comparing the luminescent properties of the free ligand and the complex, we concluded that the phosphorescence of originates from ligand centered pi --> pi* transitions. Complex 2 exhibits orange luminescence both in CH(2)Cl(2) solution at 77 K and in the solid state at ambient temperature, which was assigned to metal-to-ligand [d(M) --> pi*(pmbp)] charge transfer (MLCT). The different origin of luminescence is responsible for the different luminescent color of the Zn(II) and Pt(II) complexes.     

A family of 13 tetranuclear zinc(II)-lanthanide(III) complexes of a [3+3] Schiff-base macrocycle derived from 1,4-diformyl-2,3-dihydroxybenzene

A family of thirteen tetranuclear heterometallic zinc(II)-lanthanide(III) complexes of the hexa-imine macrocycle (L(Pr))(6-), with general formula Zn(II)(3)Ln(III)(L(Pr))(NO(3))(3)·xsolvents (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm or Yb), were prepared in a one-pot synthesis using a 3:1:3:3 reaction of zinc(II) acetate, the appropriate lanthanide(III) nitrate, the dialdehyde 1,4-diformyl-2,3-dihydroxybenzene (H(2)L(1)) and 1,3-diaminopropane. A hexanuclear homometallic zinc(II) macrocyclic complex [Zn(6)(L(Pr))(OAc)(5)(OH)(H(2)O)]·3H(2)O was obtained using a 2:0:1:1 ratio of the same reagents. A control experiment using a 1:0:1:1 ratio failed to generate the lanthanide-free [Zn(3)(L(Pr))] macrocyclic complex. The reaction of H(2)L(1) and zinc(II) acetate in a 1:1 ratio yielded the pentanuclear homometallic complex of the dialdehyde H(2)L(1), [Zn(5)(L(1))(5)(H(2)O)(6)]·3H(2)O. An X-ray crystal structure determination revealed [Zn(3)(II)Pr(III)(L(Pr))(NO(3))(2)(DMF)(3)](NO(3))·0.9DMF has the large ten-coordinate lanthanide(III) ion bound in the central O(6) site with two bidentate nitrate anions completing the O(10) coordination sphere. The three square pyramidal zinc(II) ions are in the outer N(2)O(2) sites with a fifth donor from DMF. Measurement of the magnetic properties of [Zn(II)(3)Dy(III)(L(Pr))(NO(3))(3)(MeOH)(3)]·4H(2)O with a weak external dc field showed that it has a frequency-dependent out-of-phase component of ac susceptibility, indicative of slow relaxation of the magnetization (SMM behaviour). Likewise, the Er and Yb analogues are field-induced SMMs; the latter is only the second example of a Yb-based SMM. The neodymium, ytterbium and erbium complexes are luminescent in the solid phase, but only the ytterbium and neodymium complexes show strong lanthanide-centred luminescence in DMF solution.     

Wire-type ruthenium(II) complexes with terpyridine-containing [2]rotaxanes as ligands: Synthesis, characterization, and photophysical properties

[2]Rotaxanes based on the 1,2-bis(pyridinium)ethane subset[24]crown-8 ether motif were prepared that contain a terminal terpyridine group for coordination to a transition-metal ion. These rotaxane ligands were utilized in the preparation of a series of heteroleptic [Ru(terpy)(terpy-rotaxane)]2+ complexes. The compounds were characterized by 1D and 2D 1H NMR spectroscopy, X-ray crystallography, and high-resolution electrospray ionization mass spectrometry. The effect of using a rotaxane as a ligand was probed by UV/Vis/NIR absorption and emission spectroscopy of the Ru(II) complexes. In contrast with the parent [Ru(terpy)(2)]2+ complex, at room temperature the examined complexes exhibit a luminescence band in the near infrared region and a relatively long lived triplet metal-to-ligand charge-transfer (3MLCT) excited state, owing to the presence of strong-electron-acceptor pyridinium substituents on one of the two terpy ligands. Visible-light excitation of the Ru-based chromophore in acetonitrile at room temperature causes an electron transfer to the covalently linked 4,4'-bipyridinium unit and the quenching of the MLCT luminescence. The 3MLCT excited state, however, is not quenched at all in rigid matrix at 77 K. The rotaxane structure was found to affect the absorption and luminescence properties of the complexes. In particular, when a crown ether surrounds the cationic axle, the photoinduced electron-transfer process is slowed down by a factor from 2 to 3. Such features, together with the synthetic and structural advantages offered by [Ru(terpy)2]2+-type complexes compared to, for example, [Ru(bpy)3]2+-type compounds, render these rotaxane-metal complexes promising candidates for the construction of photochemical molecular devices with a wire-type structure.     

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.     

Quantum chemical studies of mononuclear zinc species of hydration and hydrolysis

Optimal geometries, charge distributions, bond analysis, changes of Gibbs free energy, entropies and enthalpies of hydration, and hydrolysis reactions for mononuclear species of Zn(2+) including hydrated and hydrolysis complexes were investigated using quantum chemical calculations in the gas phase. Optimized geometrical structures showed that the stable hydrated and hydrolysis zinc species without outer-sphere water molecules were Zn(H(2)O)(6)(2+), Zn(OH)(H(2)O)(3)(+), Zn(OH)(2)(H(2)O)(2), Zn(OH)(3)(-), and Zn(OH)(4)(2-). Results of NPA (Natural Population Analysis) indicated that the charge on the Zn atom of the hydrated ions decreased but the charge on the zinc atom of the hydrolysis species increased with the increase of inner-sphere water molecules. NBO (Natural Bond Orbital) analyses demonstrated that hydrated and hydrolysis species of zinc were mainly electrostatic bonding compounds. Calculations of reaction energies indicated that inner-sphere water molecules became more unfavorable as the hydrolysis increased. Stepwise hydrolysis equilibrium constants decreased successively and the order remained unchanged when the inner-sphere dehydration occurred.     

A time-dependent density functional theory study on the excited state behavior of a novel T2(OH)B molecule

A novel pH-sensitive fluorescent probe T₂(OH)B was selected to theoretically investigate its excited state hydrogen bonding effects and excited state intramolecular proton transfer (ESIPT) process. First, it was verified that one intramolecular hydrogen bond is formed spontaneously in T₂(OH)B itself. Given the geometrical changes, we further confirm that the hydrogen bond should be strengthened in the first excited state. When it comes to the photoexcitation process, we present the charge redistribution around hydrogen bonding moieties facilitate the ESIPT tendency. The increased electronic densities around acceptor promote the attraction of hydrogen protons. The potential energy barrier in the constructed potential energy curves reveals that the ESIPT process of the T₂(OH)B system should be ultrafast. And comparing several nonpolar solvents, we deem solvent polarity plays little role in the ESIPT reaction. Furthermore, we also search the S₁-state transition state structure along with the ESIPT path, based on which we simulate the intrinsic reaction coordinate path. We not only confirm the ESIPT mechanism presented in this work but also clarify the ultrafast excited state process and explain previous experiment. We sincerely hope that our theoretical work could guide novel applications based on the T₂(OH)B system in future.     

Synthesis and luminescence of zinc and europium alpha-thiophene carboxylate polymer

The zinc and europium alpha-thiophene carboxylate polymer with very strong red luminescence was prepared by rheological phase reaction method from zinc acetate, europium oxide and alpha-thiophenecarboxylic acid. Molecular weight, thermal analyses and X-ray diffraction pattern were measured. 1H NMR, 13C NMR, IR, XPS, UV, excitation and emission spectra were studied. The polymer with amorphous structure and 7.565x10(5) g/mol weight-average molecular exhibited excellent solubility in common organic solvents and better thermal stability under 270 degrees C in air. The quantum yield of the polymer in acetone was 0.6 relative to quinoline in 0.05 mol/l H(2)SO(4) solution. The energy of the pi,pi(*) excited state of C(4)H(3)SCO(2)(-) can be transferred to Eu(3+) ion resulting in emission from the 5D(0)-->(7)F(j) of Eu(3+) ion through the polymeric chains. Zn(2+) can effectively enhance the luminescence of Eu(3+) in alpha-thiophenecarboxylate polymer.     

New terpyridine-containing macrocycle for the assembly of dimeric Zn(II) and Cu(II) complexes coupled by bridging hydroxide anions and pi-stacking interactions

The synthesis of the new terpyridine-containing macrocycle 2,5,8,11,14-pentaaza[15](6,6' ')cyclo(2,2':6',2' ')terpyridinophane (L) is reported. The ligand contains a pentaamine chain linking the 6,6' ' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the acid-base properties of L in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, whereas the terpyridine nitrogens are involved in proton binding only at strongly acidic pH values. L can form both mono- and dinuclear Cu(II), Zn(II), Cd(II), and Pb(II) complexes in aqueous solution. The crystal structures of the Zn(II) and Cd(II) complexes ([ZnLH](2)(micro-OH))(ClO(4))(5) (6) and ([CdLH](2)(micro-Br))(ClO(4))(5).4H(2)O (7) show that two mononuclear [MLH](3+) units are coupled by a bridging anion (OH(-) in 6 and Br(-) in 7) and pi-stacking interactions between the terpyridine moieties. A potentiometric and spectrophotometric study shows that in the case of Cu(II) and Zn(II) the dimeric assemblies are also formed in aqueous solution containing the ligand and the metals in a 1:1 molar ratio. Protonation of the complexes or the addition of a second metal ion leads to the disruption of the dimers due to the increased electrostatic repulsions between the two monomeric units.     

Excitonic luminescence of hemiporphyrazines

Metal-free hemiporphyrazine (HpH(2)) is a notoriously insoluble material possessing interesting photophysical properties. Here we report the synthesis, structure, and photophysical properties of an octahedral zinc trans-ditriflate hemiporphyrazine complex "HpH(2)Zn(OTf)(2)" that contains a neutral hemiporphyrazine ligand. The photophysical properties of hemiporphyrazine are largely unaffected by introduction of zinc(II) triflate, but a dramatic increase in solubility is observed. HpH(2)Zn(OTf)(2) therefore provides a convenient model system to evaluate the impact of aggregation on the photophysical properties of hemiporphyrazine. Soluble aggregates and crystalline materials containing planar hemiporphyrazines exhibit relatively strong absorbance of visible light (450-600 nm) and red luminescence (600-700 nm). Hemiporphyrazine monohydrate (HpH(2)·H(2)O), in contrast, has a nonplanar "saddle-shaped" conformation that exhibits very little absorbance of visible light in solution or in the solid state. Upon photoexcitation at 380 nm, HpH(2)Zn(OTf)(2) and HpH(2) exhibit multiwavelength emissions centered at 450 and 650 nm. Emissions at 450 nm are highly anisotropic, while emissions at 650 nm are fully depolarized with respect to a plane-polarized excitation source. Taken together, our results suggest that excitonic coupling of aggregated and crystalline hemiporphyrazines results in increased absorbance and emission of visible light from S(0) ? S(1) transitions that are usually symmetry forbidden in isolated species. In contrast to previously proposed theories involving excited-state intramolecular proton transfer, we propose that the multiple-wavelength luminescent emissions of HpH(2)Zn(OTf)(2) and HpH(2) are due to emissive S(1) and S(2) states in aggregated and crystalline hemiporphyrazines. These results may provide a better understanding of the nonlinear optical properties of these materials in solution and in the solid state.     

A physiochemical study of azo dyes: DFT based ESIPT process

Azo linked dye derivatives were synthesized and characterized by NMR, mass and elemental analysis. An excited state intramolecular proton transfer (ESIPT) in hydroxy Schiff base has been analyzed, and found that two distinct ground state isomers of I and II are responsible for the observed dual emission. DFT calculation on energy, dipole moment, charge distribution of the rotamers in the ground and excited states support the ESIPT process. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. By varying the addition of base concentration to hydroxy Schiff base, two isobestic points were found which confirm the equilibrium among the trans enol form, anion and the cis enol form. Fluorescence quenching with metal ions reveal that hydroxy Schiff base can be used as a new fluorescence sensor to detect the Cu(2+) ion.     

Modeling the structure,absorption spectra,and cis-trans isomerization of thiacarbocyanine dyes

The relative stability of the trans-and cis-isomers of 3,3′-diethylthiacarbocyanine (Dye1) and 3,3′-diethyl-9-methylthiacarbocyanine (Dye2)¹, as well as sections of the potential energy surfaces along the internal coordinate of the isomerization reaction, were studied using the density functional theory. Calculation of the minimum energy pathway for the isomerization reaction showed that the barrier for rotation about the C₈–C₉ bond is higher for Dye1 than for Dye2. Local minimums were found for the singlet excited state of the 8,9-cis-and trans-isomers of the dyes. In the case of the trans-isomers, substantial changes in the dye structure do not occur and the local minimum of the excited state corresponds to the geometry of the starting trans-isomers, which favors efficient fluorescence. A search for the nearest local minimum of the singlet excited state of the 8,9-cis-isomers leads to structures, which differ significantly from the starting structures, and the intensity of the S₁ → S₀ transition in those structures appears to be practically zero. The results are in agreement with experimental data on the absorption, fluorescence, and fluorescence excitation spectra of the dyes.     

TiO2纳米颗粒对钌(II)三联吡啶配合物光损伤小牛胸腺DNA能力的影响

由于极短的激发态寿命, 钌(II)三联吡啶配合物对脱氧核糖核酸(DNA)的光损伤能力低下. 设计合成了三个钌(II)三联吡啶配合物[Ru(ttp)(tpy)]^2＋ (1), [Ru(ttp-COOH)(tpy)]^2＋ (2)和[Ru(ttp-COOH)(tpy-pyr)]^2＋ (3), 其中tpy为2,2':6',2"-三联吡啶, ttp为4′-(4-甲苯基)-2,2':6',2"-三联吡啶, ttp-COOH为4′-(4-羧基苯基)-2,2':6',2"-三联吡啶, tpy-pyr为4'-(1-芘基)-2,2':6',2"-三联吡啶. 比较了TiO₂纳米颗粒对它们光损伤小牛胸腺DNA的影响. 发现TiO₂纳米颗粒在空气和氩气条件下均可显著提高配合物3光损伤DNA的能力. TiO₂纳米颗粒和配合物3间的光诱导电子转移作用及其该作用生成的钌(III)物种可能是促进配合物3对DNA光损伤的主要原因.