TPPS Aggregates Research Articles

Supramolecular Chiral Aggregation of Porphyrin Induced by Photo-Generated Triphenylamines Radical Cations.

Here, it is shown that photoirradiation triggered chiral J-aggregates formation of an achiral anionic porphyrin, TPPS (tetrakis(4-sulfonatophenyl) porphyrin), in the presence of chiral triphenylamine (TPA) derivatives. A series of chiral triarylamines linked with aromatic rings is designed through urea or amide bonds. UV-irradiation of self-assembled urea-linked triphenylamine derivatives causes the formation of persistent radical cations in the chlorinated solvents, which subsequently induces the aggregation of TPPS. Transferring chirality of TPA derivatives to achiral TPPS J-aggregates leads to the chiral assemblies with remarkable chiroptical signals. The experimental results demonstrate that, TPA derivatives linked by the urea bond can effectively promote the aggregation of TPPS rather than those with the amide bond although the photo-generated radical cations are both produced. It is suggested that the urea-linked TPA derivatives are more favorable to stable radical cations and thus cause the formation of TPPS chiral J-aggregation. This work may open up an avenue for designing photo-modulated chiral supramolecular assemblies.

More Than 50-Fold Enhanced Nonlinear Optical Response of Porphyrin Molecules in Aqueous Solution Induced by Mixing Base and Organic Solvent

The difference absorption spectrum (DAS) of porphyrin molecules (tetraphenyl-porphyhrin sulfonic acid, TPPS) in aqueous solution induced by continuous wave laser irradiation has been reported previously. It was interpreted that the DAS was caused by the formation of TPPS aggregates induced by laser irradiation. However, transient spectra similar in their shape have already been reported and are attributed to the excited-state absorption and saturable absorption (SA) effects due to the triplet state formation in TPPS. In the present study, we investigated the triplet quenching effect by O2 on the DAS of TPPS aqueous solution and revealed that it originated from the triplet state formation. We also found that mixing the appropriate amount of MeOH and NaOH in TPPS aqueous solution increased its absorbance change by more than 50 times. This may be due to the decrease in dissolved oxygen concentration by mixing them. This result suggests the possibility of controlling the performance of NLO materials by adjusting the solvent mixture ratio and base/acid concentration.

Solvent Effects in Highly Efficient Light-Induced Molecular Aggregation

It has been reported that when irradiated with laser light non-resonant with the main absorption peaks, porphyrin molecules (4-[10,15,20-tris(4-sulfophenyl)-21,24-dihydroporphyrin-5-yl]benzenesulfonic acid, TPPS) in an aqueous solution become 10,000 to 100,000 times more efficient in light-induced molecular aggregation than expected from the ratio of gradient force potential to the thermal energy of molecules at room temperature. To determine the mechanism of this phenomenon, experiments on the light-induced aggregation of TPPS in alcohol solutions (methanol, ethanol, and butanol) were performed. In these alcohol solutions, the absorbance change was orders of magnitude smaller than in the aqueous solution. Furthermore, it was found that the absorbance change in the aqueous solution tended to be saturated with the increase of the irradiation intensity, but in the ethanol solution, the absorbance change increased linearly. These results can be qualitatively explained by the model in which intermolecular light-induced interactions between molecules within a close distance among randomly distributed molecules in the laser irradiation volume are highly relevant to the signal intensity. However, conventional dipole–dipole interactions, such as the Keesom interaction, are not quantitatively consistent with the results.

Core-Assisted Formation of Porphyrin J-Aggregates in pH-Sensitive Polyelectrolyte Microcapsules Followed by Fluorescence Lifetime Imaging Microscopy.

A strategy assisted by an inorganic template was developed to promote the organized self-assembly of meso-(tetrakis)-(p-sulfonatophenyl)porphyrin (TPPS) on pH-sensitive core-shell polyelectrolyte microcapsules (PECs) of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH). A key feature of this strategy is the use of template CaCO3 microparticles as a nucleation site endorsing inside-outside directional growth of porphyrin aggregates. Using this approach, TPPS self-assembly in positively charged PECs with CaCO3 (PAH/PSS)2PAH as a sequence of layers was successfully achieved using mild pH conditions (pH 3). Evidence for porphyrin aggregation was obtained by UV-vis with the characteristic absorption bands in PECs functionalized with porphyrins. Fluorescence lifetime imaging microscopy (FLIM) of the polyelectrolyte core-shell confirmed the presence of radially distributed needlelike structures sticking out from polyelectrolyte shells. Microscopic images also revealed a sequential process (adsorption, redistribution, and aggregation) for the directional growth (inside/outside) of TPPS aggregates, which highlights the importance of the core in the aggregation induction. Removing the CaCO3 core alters the porphyrin interaction in the PEC environment, and aggregate growth is no longer favored.

Adsorption behavior and self-aggregation of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin on quaternized polysulfone membrane

Adsorption of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) on the quaternized polysulfone (QAPSF) porous membrane based on the electrostatic interaction was investigated. TPPS species in solution showed different adsorption behavior. The diacid (H4TPPS2−) form of the porphyrin at pH 4.0 showed almost equal adsorption capacity, while slower adsorption rate on the QAPSF membrane, compared with the free-base (H2TPPS4−) form at pH 7.0; J-aggregates of TPPS in aqueous solution affected the adsorption. Compared with in the aqueous solution, the apparent pK a for the equilibrium between H4TPPS2− and H2TPPS4− of the adsorbed porphyrin was significantly decreased by the interaction between TPPS and QAPSF. J-type aggregation of TPPS can also occur on the membrane, while much lower pH is required. The pH dependency was considerably influenced by adsorption capacity; higher adsorption capacity was in favor of the protonation and J-aggregation at relative higher pH.

Aggregation Behavior of the Template-Removed 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin Chiral Array Directed by Poly(ethylene glycol)-block-poly(l-lysine)

Complexation between 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(ethylene glycol)-block-poly(L-lysine) (PEG-b-PLL) was performed via electrostatic interaction. Two kinds of primary arrays of TPPS with different supramolecular chirality induced by PLL were obtained in the resultant complex by inverting the mixing procedure of the two components. These arrays could be displaced by poly(sodium-p-styrenesulfonate) (PSS) from the chiral PLL template through competitive electrostatic complexation, and then PSS formed a polyion complex micelle with PEG-b-PLL. The template-removed TPPS arrays preserved their induced chirality and served as primary subunits for the secondary aggregation of TPPS. The morphology of the secondary aggregates was strongly dependent upon the asymmetric primary supramolecular arrangement of TPPS. The rodlike nanostructure that was ∼200 nm in length was composed of the primary arrays that showed opposite exciton chirality between the J- and H-bands. In contrast, the micrometer-sized fibrils observed were composed of the arrays with the same exciton chirality at the J- and H-bands.

A strategy to stabilize the confined chiral TPPS J-aggregate by ionic block copolymer

Poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP), with a poly-cation building block, forms electrostatic complexes with the J-type chiral pre-aggregates of 5,10,15,20-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) in the water inner-phase of the TX-100 reverse microemulsion at pH 1.0 using l-tryptophan as the chiral source. The complexation with PEG45-b-P4VP6 prevents these chiral pre-aggregates from contacting with each other during the percolation of the droplets, so as to stabilize the circular dichroism intensity and the size of the complexes. After breaking the microemulsion, the PEG45-b-P4VP6/TPPS aggregates are also prevented from further clustering at optimized ratio of [polymer]/[TPPS], so these complex aggregates disperses in acetone with spherical morphology and well maintain their size and chiral signal for further storing. This method can be considered as one of extracting the confined chiral aggregates as an isolated form apart from the reverse microemulsion.

Chiral Conversion and Memory of TPPS J-aggregates in Complex Micelles: PEG-b-PDMAEMA/TPPS

In the presence of tryptophan (Trp), complex micelles were prepared by 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (TPPS) and poly(ethylene glycol)-block-poly(2-(dimethylamino)ethyl methylacrylate) (PEG-b-PDMAEMA) in aqueous solutions at pH 1.8. Different mixing sequences led to different morphologies. Spheres and nanorods of small size were obtained in sequence I (P/Trp+TPPS) where TPPS was added into the mixed solution of PEG-b-PDMAEMA and Trp. More nanorods of larger length were achieved in sequence II (TPPS/Trp+P) where the copolymer was added as the last component. Two types of supramolecular chirality of TPPS aggregates caused by mixing sequences were investigated. In (P/Trp+TPPS), the circular dichroism (CD) signal of H-band was in line with the chirality of Trp while that of J-band exhibited an opposite signal (Chirality I). In (TPPS/Trp+P), chiral signals at both H- and J-bands followed that of Trp (Chirality II). The conversion between the two types of chirality can be accomplished by modulating the molar ratio of the repeating units on block PDMAEMA to TPPS, or a cycle of pH 1.8-5.5-1.8 processing on the micelle solution. In addition, the supramolecular chirality can be memorized via strong electrostatic interaction with achiral copolymer even after removal of the chiral template, but only Chirality II can be cyclically "switched-off-on".

Effect of Ionic Liquid on J-Aggregation ofmeso-Tetrakis(4-sulfonatophenyl)porphyrin within Aqueous Mixtures of Poly(ethylene glycol)

Aqueous mixtures of poly(ethylene glycol) (PEG) of different compositions offer widely varying physicochemical properties that may support porphyrin aggregation. Aggregation behavior of a common water-soluble porphyrin, meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS), is investigated within aqueous PEG mixtures constituted of PEGs of average molecular weights 200 (PEG200), 400 (PEG400), 600 (PEG600), and 1000 (PEG1000) using UV-vis molecular absorbance, steady-state fluorescence, and resonance light scattering techniques. No aggregation of TPPS is observed in neat PEGs; addition of 10 wt % water to PEG at pH 1.0 is found to trigger TPPS into significant J-aggregation. The J-aggregation is observed to be most efficient within an aqueous mixture of 90 wt % PEG1000 at pH 1.0. The effect of ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]), as additives on the J-aggregation efficiency of TPPS within aqueous mixtures of PEG400 at pH 1.0 is investigated and compared with the effect of salts NaCl, NaPF(6), and NaBF(4) as additives on the J-aggregation of TPPS under the same conditions. In an aqueous mixture of 10 wt % PEG400 at pH 1.0, ionic liquids are observed to increase the J-aggregation efficiency more than the salts at lower concentrations. The efficiency of J-aggregation decreases upon further addition of [bmim][BF(4)] due to reduced dissociation of this ionic liquid in the mixture. While the three salts show limited solubility, the two ionic liquids are completely miscible in a 90 wt % PEG400 mixture in water at pH 1.0. The J-aggregation efficiency of TPPS increases rapidly and reaches a maximum before decreasing gradually as more and more ionic liquid is added to the mixture. The results draw attention to the unique dual role of ionic liquids as additives in affecting the J-aggregation of TPPS within aqueous mixtures of PEG as well as to their proficiency over common salts in J-aggregation.

Micellization of copolymers via noncovalent interaction with TPPS and aggregation of TPPS

Aggregation of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) was investigated in complex micelles composed of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP) and poly(2-(dimethylamino)ethyl methylacrylate)-b-poly(N-isopropylacrylamide) (PDMAEMA-b-PNIPAM) in aqueous solutions. The resultant complex micelles had a complex P4VP/PDMAEMA/TPPS core and a mixed PEG/PNIPAM shell. Different noncovalent interaction modes between the porphyrin and each copolymer accomplished a co-effect on the aggregation of TPPS. The formation of aggregates was pH-dependent. At pH 3.2–6.5, TPPS existed as a mixture of H-aggregates and monomers because of the aromatic-aromatic interaction with P4VP and electrostatic interaction with PDMAEMA. The monomers translated into J-aggregates, stabilized by electrostatic interaction with the both polyelectrolyte blocks, upon decreasing the pH to 1.6. The free-base monomer was the one and only form for the dye at pH 11.0 due to aromatic stacking with the pyridyl rings.

Ionic liquid induced spontaneous symmetry breaking: emergence of predominant handedness during the self-assembly of tetrakis(4-sulfonatophenyl)porphyrin (TPPS) with achiral ionic liquid

The self-assembly and supramolecular chirality of a dianionic tetrakis(4-sulfonatophenyl) porphyrin (TPPS) in the presence of ionic liquids, 1-alkyl-3-methylimidazolium tetrafluoroborate (alkyl = C(2), C(4) or C(6), abbreviated as C(2)mimBF(4), C(4)mimBF(4) and C(6)mimBF(4), respectively), have been investigated. It has been confirmed that mimBF(4) ionic liquids significantly promoted the J-aggregation of TPPS and the alkyl chain length in the imidazolium cation was closely related to the TPPS aggregation, the inducing ability of which decreased in the order of C(2), C(4) or C(6) in side chain. Interestingly, the formed TPPS assemblies with the ionic liquids showed supramolecular chirality although both TPPS and ionic liquids are achiral. It was found that the supramolecular chirality of the TPPS/IL system always appeared after the formation of the J aggregate. The dynamic process of the emergence of the handedness in the initial achiral system was monitored by the time-dependent CD spectra. A mechanism for the transformation of the conventional J-aggregate to the chiral J-aggregate was proposed. The work will lead to a deeper understanding of the chiral symmetry breaking in the supramolecular system.

Polyion micelles with diphase-segregated core: electrostatic self-assembly of poly(ethylene glycol)-block-poly(4-vinylpyridium) and tetrakis (4-sulfonatophenyl) porphyrin in solution

The polyion micelles were prepared with poly(ethylene glycol)-block-poly(4-vinylpyridium) (PEG114-b-P(4-VPH+)35) and tetrakis (4-sulfonatophenyl) porphyrin (TPPS) in acid aqueous solution. Micellization was investigated by using a combination of static and dynamic laser scattering. UV–Vis spectroscopy revealed that the H- and J-type aggregates of TPPS were formed in the micellar core. Transmission electron microscopy studies of the polyion micelles show that the obtained polyion micelles take a diphase-segregated core, the polymer phase and the incompatible TPPS aggregates phase.

Complex aggregation of TPPS and PEG-b-P4VP in confined space

To explore the structure and property features of complex aggregates assembled by polymer and organic dye molecules in microcosmic soft confined space, a three-dimensional microconfinement is constructed by W/O inverse emulsion as the site for the complex aggregation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP). It is found that porphyrin molecules exist in emulsion droplets mainly as the deprotonated monomer form, even though the pH of the water phase is much lower than the pK(a) of TPPS in bulk (pK(a)≈ 4.7). In spatially confined circumstances, upon blending of the single-component emulsions, complex aggregates are formed due to the thermodynamic collision of emulsion droplets and the subsequent electrostatic interaction between TPPS and polymer. The resultant novel complexes possess a relatively precise structure and homogenous core consisting of a porphyrin and P4VP block. Upon emulsion-breaking, the metastable complex kinetic intermediates generated in original acidic emulsion droplets display a remarkable trend of reaggregation within a certain period of time followed by a disassociation and redispersion. Complex aggregates with some novel morphologies are observed. The final product has a core-shell structure with the electrostatic complex of deprotonized porphyrin molecules homogenously dispersing in the P4VP clew as the core and the soluble PEG as the shell. However, those complexes produced in basic emulsion droplets exhibit a relatively higher stability against further aggregation after breakage of emulsion.

J-aggregation of ionic liquid solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin

The title porphyrin was dissolved in the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim][BF(4)], and triggered to assemble into J-aggregates by the addition of incremental volumes of water containing various amounts of acid (0.1, 0.2, or 1.0 M HCl). In contrast to recent studies, the current investigation is unique in that it centers on media that contain a predominant ionic liquid component (2.9-5.4 M [bmim][BF(4)]), as opposed to an aqueous electrolyte containing a small fraction of ionic liquid as dissociated solute. Complex aggregation and underlying photophysical behavior are revealed from absorption spectroscopy, steady-state fluorescence, and resonance light scattering studies. Upon addition of aqueous HCl, the efficient formation of H(4)TPPS(2-) J-aggregates from the diprotonated form of meso-tetrakis(4-sulfonatophenyl)porphyrin (H(2)TPPS(4-)) occurs in [bmim][BF(4)]-rich media in a manner highly dependent upon the acidity, TPPS concentration, and solvent composition. The unique features of TPPS aggregation in this ionic liquid were elucidated, including the surprising disassembly of J-aggregates at higher aqueous contents, and our results are described qualitatively in terms of the molecular exciton theory. Finally, the potential of this system for the optical sensing of water at a sensitivity below 0.5 wt% is demonstrated. Overall, our findings accentuate how little is known about functional self-assembly within ionic liquids and suggest a number of avenues for exploring this completely untouched research landscape.

Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic Interactions

Supramolecular chirality in two configurational homoaggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D- and L-alanine in acidic water (see picture). The chirality can be further memorized and enforced through strong electrostatic interactions between TPPS aggregates and achiral poly(allylamine) [PAA].Supramolecular chirality in two configurational homoaggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D- and L-alanine (Ala) in acidic water, respectively. The induced supramolecular chirality can be further memorized and enforced, even after complete removal of Ala or in the presence of excess Ala with the opposite configuration, through strong electrostatic interactions with achiral poly(allylamine) [PAA]. The ionic chiral interactions between TPPS and Ala or PAA are characterized by means of UV/Vis absorption and circular dichroism spectrometry. Fluorescence spectroscopy and atomic force microscopy are used as complementary techniques. On the basis of the comprehensive experimental results, a possible mechanism for chiral induction, memory, and amplification of TPPS homoaggregates by chiral amino acids and achiral PAA is proposed. Thus, we demonstrate a novel strategy to realize chiral memory in supramolecular systems by polyelectrolytes through hierarchical electrostatic self-assembly.

PH-Controlled Self-Assembling of meso-Tetrakis(4-sulfonatophenyl)porphyrin−Chitosan Complexes

Solid meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS(4))-chitosan supramolecular complexes were prepared by addition of porphyrin to an aqueous solution of chitosan at pH values. The precipitates obtained were assigned as 1 (pH 6.8) and 2 (pH 2.5) and characterized by spectroscopic, thermal, and microscopic methods. Spectroscopic investigation confirmed the presence of TPPS(4) and chitosan in both products and that the porphyrin is highly self-associated. H-type (stacked) of TPPS(4) aggregation was proposed for 1 and J-type (tilted) for 2. Thermal analysis revealed different pyrolysis routes of the complexes depending on their structural diversity. Light microscopic analysis indicated fibrous and lamellar microstructures, respectively, for 1 and 2. SEM and AFM analysis showed that both complexes consist of compact nanostructures; their size and interconnection is different for 1 and 2. Based on structural inferences, self-assembling hierarchy models were proposed for both of the TPPS(4)-chitosan supramolecular complexes.

Induced Circular Dichroism of Anionic Porphyrin TPPS Aggregates in DNA Solutions

Induced circular dichroism (CD) of achiral anionic tetrakis (4-sulfonatophenyl) porphine (TPPS) in polyanionic DNA solutions was investigated. Induced CD signals of the anionic TPPS aggregates in both cholesteric liquid crystal DNA solutions and isotropic DNA solutions are all observed within an appropriate pH range. When the pH value is less than 5, the induced CD signals of TPPS are split in the isotropic DNA solutions, which should result from the helical arrangement of TPPS molecules within the TPPS aggregates with L- or D-type helix. The induced CD signals without splitting of TPPS aggregates in the cholesteric liquid crystal DNA solutions should result from the helical arrangement of the aggregates like molecule screwing along the cholesteric helix axis. When the pH value is higher than 5.2, no induced CD can be observed in the isotropic solutions and the cholesteric liquid crystal DNA solutions, because the electrostatic repulsion force between the non-protonated TPPS molecules and the bases on DNA chains prevents the chiral induction. The mechanism of the different induced CD signals of TPPS aggregates in the DNA solutions is discussed.

Highly sensitive spectrophotometric determination of cationic surfactants in ground waters as their Cu(II)–TPPS aggregates preceded by solid-phase fractionation

A highly sensitive spectrophotometric determination of cationic surfactants in ground waters was established by forming their Cu(II)–TPPS aggregates, preceded by solid-phase extraction with an SCX cartridge. Cationic surfactants (CSs) were quantitatively trapped and isolated by the SCX solid phase. The use of Cu(II)–TPPS anionic chromophore could reduce the interference by unintentional metal ions coexisting in surrounding waters. The method was very sensitive in the determination of CSs less than 10 −5 M levels with acceptable recovery and calibration data. The colorimetric sensitivity was very dependent on the alkyl-chain length of the surfactants, and a CS having 23 carbon atoms gave the highest sensitivity. Overall recoveries were 95–97% with R.S.Ds. less than 3% in the cases over 10 −6 M levels. In the cases in 10 −7 M levels, however, a portion of the analyte would be adsorbed by reservoir walls, which could seriously affect the trace determination. The preliminary addition of 4,4′-bipyridyl into the sample solution was effective in decreasing such unintentional analyte losses, leading up to 73% recovery. The developed method was applied to the analysis of river water at ppb levels of CSs with a fractional concentration through a SCX solid phase subjected by 500-mL aliquots of sample.

Inhibition of aggregation of meso-tetra(4-sulfonatophenyl)-porphyrin (H4TPPS) by urea

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin ( H 4 TPPS ) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl , diacid TPPS ( H 4 TPPS ) exists as a monomer up to 75 μM H 4 TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H 4 TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 105 M -1. cm -1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H 4 TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D 2 O at pH 2, no aggregation is observed. These spectral observations suggest that the H 4 TPPS aggregation involves intermolecular hydrogen bonding.

Study of Internal Structure of meso-Tetrakis (4-Sulfonatophenyl) Porphine J-Aggregates in Solution by Fluorescence Microscope Imaging in a Magnetic Field

To determine the internal molecular arrangement of organic dye aggregates, a technique for observing the fluorescence microscope image of a solution consisting of dye aggregates in a magnetic field was developed. Using this technique, the fluorescence image of meso-tetrakis (4-sulfonatophenyl) porphine (TPPS) J-aggregates in a solution in a magnetic field of 10 T was observed. It was observed that individual rod-shaped TPPS aggregates (4-20 microm in length) were aligned parallel to the applied field. The polarized absorption spectra of the sample solution were also measured in the fields of up to 10 T. The spectra show the magnetic field dependence of the J-band intensity, reflecting the magnetic alignment of the aggregates. On the basis of the magnetic and optical properties obtained by the experiments, it was proposed that TPPS J-aggregates have a tube-like structure and are constructed from one-dimensional molecular arrays that are stacked parallel to the long axis of the tube.