Effects of cyclodextrins on the complexation between Methylene Blue and tetrakis(4-sulfonatophenyl)porphyrin in aqueous solutions

In aqueous solutions buffered at pH 10.1, Methylene Blue (MB) forms a complex with tetrakis(4-sulfonatophenyl)porphyrin (TSPP). The equilibrium constant for the formation of the MB-TSPP complex has been evaluated to be 2.35 x 10(5) mol(-1) dm3 from the fluorescence quenching of MB by TSPP. Effects of alpha-, beta-, and gamma-cyclodextrin (CD), and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin on the complexation between MB and TSPP have been examined by means of absorption and fluorescence spectroscopy. The binding of CDs to TSPP and/or MB in the MB-TSPP complex causes the dissociation of the MB-TSPP complex.     

Photoinduced interaction between riboflavin and TiO(2) colloid

The adsorption of riboflavin on the surface of TiO(2) colloidal particles and the electron transfer process from its singlet excited state to the conduction band of TiO(2) were examined by absorption and fluorescence quenching measurements. The apparent association constants (K(app)) were determined. The quenching mechanism is discussed involving electron transfer from riboflavin to TiO(2).     

An investigation on electron transfer quenching of zinc(II) meso-tetraphenylporphyrin (ZnTPP) by colloidal TiO(2)

The interaction of zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal TiO(2) was studied by absorption, steady state and time-resolved fluorescence spectroscopy. The quenching was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear in the range of quencher concentration used 0-5 x 10(-4)M. The bimolecular quenching rate constants (k(q)) were 20.5 x 10(10)M(-1)s(-1) (steady-state) and 2.85 x 10(10)M(-1)s(-1) (time resolved). The quenching process is suggested to involve electron transfer from the ZnTPP to TiO(2) considering the experimental evidences obtained.     

Cyanobacterial chlorophyll as a sensitizer for colloidal TiO2

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO(2) through electrostatic interaction was observed. The apparent association constant (K(app)) of chlorophyll-TiO(2) obtained from absorption spectra is 3.78x10(4)M(-1). The K(app) value of chlorophyll-TiO(2) as determined from fluorescence spectra is 1.81x10(4)M(-1), which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between chlorophyll and colloidal TiO(2) nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO(2) nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (k(et)) for electron injection from the excited state chlorophyll into the conduction band of TiO(2) is 4.2x10(8)s(-1).     

Different Interactions between Isomeric Tetrakis-(N-Hexadecylpyridiniumyl) Porphyrins and CdS Nanoparticles

Using porphyrin amphiphiles TC(16)PyP(2), TC(16)PyP(3), and TC(16)PyP(4) as photosensitizers, the interaction between amphiphilic porphyrins and colloidal CdS nanoparticles was studied by observing their absorption spectra, fluorescence spectra, and fluorescence lifetimes. The experimental results reveal that upon addition of CdS nanoparticles to a TC(16)PyP(3) or TC(16)PyP(4) solution, TC(16)PyP(3) or TC(16)PyP(4) is adsorbed onto the surface of the colloidal nanoparticles due to electrostatic action. The absorption spectra display the characteristic absorption of metalloporphyrin. Moreover, this adsorption also leads to red-shifted fluorescence spectra and the quenching of fluorescence emission. These changes are related to the formation of complexes. Nearly 90% of the fluorescence emission of 5x10(-6) mol/L TC(16)PyP(4) can be quenched with 6.8x10(-4) mol/L CdS colloid nanoparticles. Only 60% of the fluorescence emission of 5x10(-6) mol/L TC(16)PyP(3) can be quenched with 6.8x10(-4) mol/L CdS nanoparticles. The fluorescence quenching is attributable mainly to static quenching. According to the fluorescence quenching curves, the apparent association constants of TC(16)PyP(4) and TC(16)PyP(3) with colloidal CdS nanoparticles are 1.42x10(3) (mol/L)(-1) and 6.76x10(2) (mol/L)(-1), respectively. However, TC(16)PyP(2) does not adsorb onto the surface of colloid nanoparticles due to its larger steric hindrance; its absorption and fluorescence spectra are unchanged. Copyright 2000 Academic Press.     

方菁染料敏化二氧化钛超微粒的光化学行为

通过吸收光谱、荧光猝灭、单光子计数等手段研究了2-(4-乙胺-2-羟基苯基)-4-(4-乙胺-苯基)-方菁染料(SQ)在TiO2超微粒体系中的光化学行为。结果表明, SQ强烈吸附在TiO2胶粒表面, 表观吸附常数为2.275×10^3mol^-^1 . dm^3。SQ的荧光能被TiO2有效地猝灭,猝灭的效率达97%。根据物质的氧化还原电位、光谱特性及荧光寿命的变化提出光诱导电子界面转移的荧光猝灭机理, 电子转移的速率常数为1.97×10^8s^-^1。     

Interaction between certain porphyrins and CdS colloids: a steady state and time resolved fluorescence quenching study

The interaction between porphyrins namely, meso-tetrakis (4-methoxyphenyl)porphyrin (TMeOPP), protoporphyrin IX (PPIX) and Zinc(II) meso-tetraphenylporphyrin (ZnTPP) with colloidal CdS has been studied by using steady state and time resolved fluorescence quenching measurements. The porphyrins adsorbed on the surface of colloidal CdS due to electrostatic interaction. This adsorption leads to changes in the absorption spectra related to the complex formation. The apparent association constant (Kapp) was in the order of 4.34-5.58 x 10(5) M(-1) from the effect of colloidal CdS on the absorption spectra and 0.64-1.6 x 10(5) M(-1) from fluorescence quenching data. Quenching is attributable mainly to static mechanism through ground state complex formation as confirmed by lifetime measurements.     

Nanosecond time-resolved studies of long-lived photoinduced charge separation in the dyad fluorescein-anthraquinone-methyl ester adsorbed on TiO2 colloids

A dyad composed of fluorescein and 2-methyl-anthraquinone (FL-AQ) was synthesized and its photophysical properties were examined by absorption, fluorescence spectroscopy, and fluorescence lifetime. The charge-separated state formed by photoinduced intramolecular electron transfer was detected by nanosecond transient absorption spectroscopy for the first time. When FL is excited in solution, the photoinduced electron transfer from FL to AQ proceeds efficiently. The rate constant and the efficiency of intramolecular electron transfer are 3.95 x 10(9) s(-1) and 95%, respectively. Its charge-separated state lifetime is too short to detect by transient absorption spectroscopy. Adding nanometer colloidal TiO(2) to an FL-AQ ethanol solution prolongs the lifetime of the charge-separated state, so its transient absorption signal is recorded significantly. The lifetimes of FL(+). at 480 nm and AQ(-). at 560 nm in the FL-AQ/TiO(2) colloidal system are 11.1 and 8.93 mivros, respectively.     

Counterion-dependent excitonic spectra of tetra(p-carboxyphenyl)porphyrin aggregates in acidic aqueous solution

Aggregates of the diacid form of tetra(p-carboxyphenyl)porphyrin (TCPP) are found to be stabilized in aqueous solution at low pH in the presence of poly(vinyl alcohol). At pH values in the range from about 1 to 4, a split Soret band is observed which is independent of counterion and tentatively assigned to a dimer species. As the pH is made lower than 1, the spectra evolve to reveal the presence of porphyrin aggregates. As in the case of the well-known aggregates of the related tetra(p-sulfonatophenyl)porphyrin (TSPP) diacid, the concentration of spectroscopically distinguishable aggregates increases with increasing ionic strength or decreasing pH. Unlike aggregates of TSPP, however, TCPP aggregates below pH 1 have visible absorption spectra which depend on the counterion, which is Cl(-) or NO(3)(-) in this study. In this work, we present visible absorption, light-scattering, and resonance Raman spectra of TCPP diacid in its monomer, dimer, and aggregated forms and attempt to understand the structural basis for counterion-dependent structure and excitonic coupling in the aggregates. Evidence is presented for intercalation of inorganic counterions between porphyrin molecules in the aggregate, an effect which to our knowledge has not been previously reported.     

Electronic and fluorescence spectral studies of a novel porphyrin-polypyridyl ruthenium(II) hybrid linked by a butyl chain

The electronic and fluorescence spectroscopic properties of a novel porphyrin-polypyridyl ruthenium(II) hybrid, [C(4)-TPP-(ip)Ru(phen)(2)](ClO(4))(2) (TPP=5,10,15,20-tetraphenylporphyrin, ip=imidazo[4,5-f][1,10]phenanthroline and phen=1,10-Phenanthroline), in which a polypyridyl ruthenium(II) moiety is linked to a porphyrin moiety by a butyl chain have been investigated and compared to its corresponding reference compounds. The studies of electronic absorption spectra have shown that there is an electronic interaction between the porphyrin moiety and the polypyridyl ruthenium(II) moiety in the hybrid. It can be found that intramolecular photoinduced electron and energy transfer processes may occur in the hybrid from the fluorescence spectra. When exciting in Soret band and Q band of porphyrin, the fluorescence quenching of the porphyrin moiety of the hybrid takes place due to electron transfer from the lowest singlet excited state (S(1)) to the appended polypyridyl rutherium(II) moiety, while the decay of S(2) (the second-excited singlet state) of the porphyrin moiety is mainly contributed to internal conversion to S(1). When exciting in MLCT band of the polypyridyl ruthenium(II) moiety, fluorescence corresponding to the polypyridyl ruthenium(II) moiety is quenched by intramolecular energy transfer from (3)MLCT of the ruthenium moiety to the lowest-energy triplet state localized on the porphyrin moiety.     

Molecular organization and effective energy transfer in iridium metallosurfactant-porphyrin assemblies embedded in Langmuir-Schaefer films

Mixed Langmuir monolayers and Langmuir-Schaefer (LS) films containing the cationic metallosurfactant bis(2-phenylpyridine)(4,4'-diheptadecyl-2,2'-bipyridine)-iridium(III) chloride (Ir-complex) and the anionic tetrakis(4-sulfonatophenyl)porphyrin (TSPP) in 4:1 molar ratio have been successfully prepared by the co-spreading method at the air-water interface. The presence of both luminescent species at the interface, as well as the organization of the TSPP underneath the Ir-complex matrix in Langmuir and LS films, is inferred by surface techniques such as π-A isotherms, reflection spectroscopy, Brewster angle microscopy (BAM) and UV-visible absorption spectroscopy. A red-shift in the absorption band of the porphyrin under the compression of the mixed monolayer suggests the J-aggregation of the TSPP under the Ir-complex matrix. To date, this is the first report of Langmuir and/or LS films containing these two types of species together. Furthermore, the intermolecular energy transfer between Ir-complex and TSPP molecules in solution and in transferred mixed films is investigated through steady-state fluorescence and lifetime measurements. These results indicate that effective intermolecular energy transfer occurs from the Ir-complex to the TSPP molecules in LS films. The influence of the spatial proximity of donor and acceptor molecules has been studied by the insertion of lipid interlayers among them.     

Two-photon absorption enhancement of polymer-templated porphyrin-based J-aggregates

Supramolecular structures based on organized assemblies of macrocyclic chromophores, particularly porphyrin-based dyes, have attracted widespread interest as components of molecular devices with potential applications in molecular electronics, artificial light harvesting, and pharmacology. We report the formation of J-aggregates of two porphyrin-based dyes, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TSPP, 4) and an amino tris-sulfonate analogue (5) in water using a functionalized norbornene-based homopolymer, synthesized by ring-opening metathesis polymerization (ROMP). Ionic interactions of the cationic side chains (ammonium groups) of the polymer under acidic conditions with the negatively charged sulfonate groups of the porphyrins facilitated polymer template enhanced J-aggregation of the porphyrin dyes. J-Aggregation behavior was investigated photophysically by UV-vis absorption along with steady-state and time-resolved fluorescence studies. Two-photon absorption (2PA) was enhanced by about an order of magnitude for the J-aggregated TSPP relative to its free base. Significantly, the 2PA cross section of the polymer-templated TSPP J-aggregate was up to three times higher than the J-aggregated TSPP in the absence of the polymer template while the 2PA cross section for polymer-templated J-aggregates of 5 increased substantially, up to ca. 10,000 GM, suggesting a prominent role of polymer-templating to facilitate porphyrin aggregation and greatly enhance nonlinear absorption.     

磺酸基卟啉的电化学发光研究及应用

以四(4-磺酸基苯基)卟啉（TSPP）为发光体,过硫酸钾（K₂S₂O₈）为共反应剂,构建了一个新的电化学发光（ECL）体系. 在扫描范围为0~-1.5V时,该体系出现两个阴极ECL峰,分别为TSPP的还原峰（-0.8V）和K₂S₂O₈ 的还原峰 (-1.2V). 亚甲基蓝能有效猝灭四(4-磺酸基苯基)卟啉的电化学发光,根据猝灭效率与亚甲基蓝浓度的线性关系,建立了一种测定亚甲基蓝含量的新方法.     

大环方酸多齿配体的合成及其光谱特征

合成了一种尚未见文献报道的大环方酸多齿配体，它的结构经ＩＲ、ＵＶ、１ＨＮＭＲ、ＭＳ及元素分析所证实，并考查了它的光谱特征。该化合物的最大吸收波长在７００－８００ｎｍ波长区，它在ＴｉＯ２胶体溶液中，荧光可以被有效淬灭。它与ＴｉＯ２形成的表面复合物的表观复合常数Ｋａｐｐ＝３９０５ｍｏｌ－１．Ｌ。     

Tetrakis(4-sulfonatophenyl)porphyrin fluorescence as reporter of human serum albumin structural changes induced by guanidine hydrochloride

The interaction of the drug carrier protein human serum albumin (HSA) with the ionic, free base porphyrin tetrakis(4-sulfonatophenyl)porphyrin (TSPP) was investigated under chemical denaturation conditions using guanidine hydrochloride (Gdn-HCl) in aqueous solution at pH 7 and 2.5. Protein stability was studied by fluorescence spectroscopy using intrinsic tryptophan fluorescence, whereas far-UV circular dichroism gave information regarding conformational changes. Steady-state and time-resolved fluorescence as well as extinction and induced visible CD of TSPP were also monitored in the presence of the denaturant.The addition of 1.0 M Gdn-HCl inhibited the FRET process between the sole tryptophan residue of HSA and the porphyrin as inferred by an increase in the intrinsic fluorescence of the former together with a drop in the fluorescence of the latter. Simultaneously, an induced bisignate CD band was detected in the Soret region of TSPP extinction following the changes in the monomer ? aggregate equilibrium of TSPP. The features in the extinction spectra pointed to the formation of J-aggregates at pH = 2.5 and were confirmed by fluorescence lifetime measurements. At pH = 7, no TSPP dimers were detected in the absence of the protein or in the presence of native HSA. However, H-dimers or higher aggregates of TSPP associated to HSA were induced at concentrations of Gdn-HCl below 2 M.The main unfolding transition probed by HSA intrinsic fluorescence took place between 2 and 3 M Gdn-HCl at pH = 7, whereas at pH = 2.5 it was detected only above 2.8 M Gdn-HCl, coinciding with TSPP release into solution which occurs at high denaturant concentration for both pH studied. The results suggest that the chemical unfolding of HSA is a multistep process. The free base porphyrin contributes to an increase in the protein stability, particularly important under acidic conditions, where the protein is known to be in an expanded form in the absence of TSPP.The analysis of TSPP fluorescence fluctuations in the autocorrelation functions obtained using fluorescence correlation spectroscopy (FCS) in the presence of HSA at different denaturant concentrations showed that the porphyrin only interacts with the native form of the protein.Both fluorescence and circular dichroism data confirmed that in the noncovalent complex HSA–TSPP the free base porphyrin can act as a reporter of the protein structural changes induced either by pH or chemical denaturation.     

以共价键相连的卟啉-酞菁化合物分子内能量传递及光诱导电子转移

合成了叶啉与酞菁以共价键连接起来的双发色团分子。测定了它们的吸收光谱,荧光光谱,荧光寿命等。计算了分子内能量传递过程的效率(φ_EnT)及速率常数(κ_EnT)。结果表明:在稀溶液中,卟啉与酞菁等克分子混合时,观察不到分子间能量传递过程现象的发生;而双发色团分子的分子内能量传递过程则明显发生了,其效率(φ_EnT=13～70%)与速率常数(κ_EnT=1.2×10⁷～2.0×10⁸s^-1)取决于分子的结构类型。电子转移与能量传递过程与介质性质有关。在极性溶剂中有利于电子转移过程的进行,而不利于能量传递过程;在非极性溶剂中,则有利于能量传递过程的进行,而不利于电子转移。 选择性激发酞菁发色团,观测到了只有电子转移发生的过程,其电子转移效率达到38%。     

Investigation of the interaction between colloidal TiO(2) and bovine hemoglobin using spectral methods

The interaction between bovine hemoglobin (BHb) and TiO(2) colloid was investigated by UV/vis absorption, UV/vis diffuse reflectance spectrum, IR, fluorescence, synchronous fluorescence, and three-dimensional fluorescence spectra techniques under physiological pH 7.40. TiO(2) effectively quenched the intrinsic fluorescence of BHb via static quenching. The process of binding TiO(2) on BHb was a spontaneous molecular interaction procedure. The thermodynamic parameters, DeltaH degrees and DeltaS degrees were estimated to be -78.07 kJ mol(-1), -110.93 J mol(-1)K(-1) according to the van' Hoff equation. This indicates that the van der Waals and hydrogen bonds interactions played a major role in stabilizing the TiO(2)-BHb complex. The effect of TiO(2) on the conformation of BHb was analyzed using synchronous fluorescence spectroscopy.     

卟啉/TiO2界面的相互作用研究

采用吸收光谱、荧光光谱和瞬态光伏技术研究了卟啉/TiO2体系的吸收光特性、荧光特性和光伏特性, 并研究了卟啉和TiO2之间的界面相互作用. 研究结果表明, 卟啉环在与钬原子结合前后与TiO2之间的作用不同, TiO2的粒径也影响界面的相互作用. 卟啉与粒径为10 nm的TiO2作用后, 能级发生了简并, 同时带隙发生了红移. 卟啉与粒径为56 nm的TiO2相互作用后只有特征吸收峰发生红移, 带隙和峰的数量几乎未发生变化. 这说明在粒径为10 nm的TiO2与卟啉的大π键之间出现了离域的相互作用, 这也被荧光光谱和瞬态光伏曲线所证实.     

Zinc(II) tetraarylporphyrins anchored to TiO2, ZnO, and ZrO2 nanoparticle films through rigid-rod linkers

A series of six Zn(II) tetraphenylporphyrins (ZnTPP), with a phenyl (P) or oligophenyleneethynylene (OPE = (PE) n ) rigid-rod bridge varying in length (9-30 A) and terminated with an isophthalic acid (Ipa) anchoring unit, were prepared as model dyes for the study of sensitization processes on metal oxide semiconductor nanoparticle surfaces (MO(n) = TiO(2), ZnO, and insulating ZrO(2)). The dyes were designed such that the electronic properties of the central porphyrin chromophore remained consistent throughout the series, with the rigid-rod anchoring unit allowing each porphyrin unit to be located at a fixed distance from the metal oxide nanoparticle surface. Electronic communication between the porphyrin and the rigid-rod unit was not desired. Rigid-rod porphyrins ZnTPP-Ipa, ZnTPP-P-Ipa, ZnTPP-PE-Ipa, ZnTPP-(PE)(2)-Ipa, ZnTPP-(PE)(3)-Ipa, and ZnTMP-Ipa (with mesityl substituents on the porphyrin ring) were synthesized using combinations of mixed aldehyde condensations and Pd-catalyzed cross-coupling reactions. Their properties, in solution and bound, were compared with that of Zn(II) 5,10,15,20-tetra(4-carboxyphenyl)porphyrin ( p-ZnTCPP) as the reference compound. Solution UV-vis and steady-state fluorescence spectra for all six rigid-rod-Ipa porphyrins were almost identical to each other and to that of p-ZnTCPP. Cyclic voltammetry and differential pulse voltammetry scans of the methyl ester derivatives of the six rigid-rod-Ipa porphyrins, recorded in dichloromethane/electrolyte, exhibited redox behavior typical of ZnTPP porphyrins, with the first oxidation in the range +0.99 to 1.09 V vs NHE. All six rigid-rod-Ipa porphyrins and p-ZnTCPP were bound to metal oxide (MO(n) = TiO(2), ZnO, and insulating ZrO(2)) nanoparticle films. The Fourier transform infrared attenuated total reflectance spectra of all compounds bound to MO n films showed a broad band at 1553-1560 cm(-1) assigned to the v(CO(2)(-)) asymmetric stretching mode. Splitting of the Soret band into two bands at 411 and 423 nm in the UV-vis spectra of the bound compounds, and broadening and convergence of both fluorescence emission bands in the fluorescence spectra of the porphyrins bound to insulating ZrO(2) were also observed. Such changes were less evident for ZnTMP-Ipa, which has mesityl substituents on the porphyrin ring to prevent aggregation. Steady-state fluorescence emission of rigid-rod-Ipa porphyrins bound to TiO(2) and ZnO through the longest bridges (>14 A) showed residual fluorescence emission, while fluorescence quenching was observed for the shortest compounds.     

Interaction of water‐soluble tetrakis‐(1‐methyl‐4‐pyridiniyl)‐porphyrin and CdS naonoparticles

The interaction between positively charged porphyrin TMPyP(4) (tetrakis‐(1‐methyl‐4‐pyridiniyl) porphyrin) and negatively charged surface of colloidal CdS nanoparticles has been studied by absorption spectrum, fluorescence spectroscopy, and time‐correlated single‐photon‐counting methods. Addition of CdS colloid to a TMPyP(4) solution leads to TMPyP(4) adsorption onto the surface of CdS colloid with an apparent association constant of 4643 L/mol. This adsorption results in distinct changes in absorption spectrum of TMPyP (4) and the quenching of its′ fluorescence, but the biexponential fluorescence decay changes hardly. Nearly 90% of the fluorescence of 5 × 10^?6 mol/L TMPyP(4) can be quenched with 1.5 × 10^?4 mol/L CdS colloid. These spectral changes are attributed to the formation of a certain form complex TMPyP(4)‐CdS.