A New Series of C‐6 Unsubstituted Tetrahydropyrimidines: Convenient One‐Pot Chemoselective Synthesis,Aggregation‐Induced and Size‐Independent Emission Characteristics

A new series of C‐6 unsubstituted tetrahydropyrimidines 6 have been directly synthesized via a convenient urea‐catalyzed chemoselective five‐component reaction (5CR) under mild conditions. Compounds 6 show typical aggregation‐induced emission enhancement (AIEE) characteristics because they are practically no emissive in solution but emit blue or green fluorescence in aggregates with fluorescence yield up to 93 %. One of the 5CR products, 6 aa , exhibits blue‐ and green‐fluorescence aggregates (bf‐ and gf‐aggregates). The bf‐ and gf‐aggregates are prepared under different conditions and proved to result from different J‐aggregations by single‐crystal X‐ray analysis. In addition, the bf‐ and gf‐aggregates of 6 aa show unusual size‐independent emission (SIE) characteristics because their maximum emission wavelengths in different sizes (suspension particles, film, powder and crystals) are the same, 434 and 484 nm, respectively. Based on the obtained experimental results, the 5CR mechanism, the origins of AIEE and SIE characteristics are discussed.     

Novel temperature‐ and pH‐responsive graft copolymers composed of poly(L‐glutamic acid) and poly(N‐isopropylacrylamide)

A series of novel temperature‐ and pH‐responsive graft copolymers, poly(L ‐glutamic acid)‐g‐poly(N‐isopropylacrylamide), were synthesized by coupling amino‐semitelechelic poly(N‐isopropylacrylamide) with N‐hydroxysuccinimide‐activated poly(L ‐glutamic acid). The graft copolymers and their precursors were characterized, by ESI‐FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (¹H NMR). The phase‐transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering. The solution behavior of the copolymers showed dependence on both temperature and pH. The cloud point (CP) of the copolymer solution at pH 5.0–7.4 was slightly higher than that of the solution of the PNIPAM homopolymer because of the hydrophilic nature of the poly(glutamic acid) (PGA) backbone. The CP markedly decreased when the pH was lowered from 5 to 4.2, caused by the decrease in hydrophilicity of the PGA backbone. At a temperature above the lower critical solution temperature of the PNIPAM chain, the copolymers formed amphiphilic core‐shell aggregates at pH 4.5–7.4 and the particle size was reduced with decreasing pH. In contrast, larger hydrophobic aggregates were formed at pH 4.2. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4140–4150, 2008     

Design and proof of reversible micelle‐to‐vesicle multistimuli‐responsive morphological regulations

Multistimuli‐responsive precise morphological control over self‐assembled polymers is of great importance for applications in nanoscience as drug delivery system. A novel pH, photoresponsive, and cyclodextrin‐responsive block copolymer were developed to investigate the reversible morphological transition from micelles to vesicles. The azobenzene‐containing block copolymer poly(ethylene oxide)‐b‐poly(2‐(diethylamino)ethyl methacrylate‐co‐6‐(4‐phenylazo phenoxy)hexyl methacrylate) [PEO‐b‐P(DEAEMA‐co‐PPHMA)] was synthesized by atom transfer radical polymerization. This system can self‐assemble into vesicles in aqueous solution at pH 8. On adjusting the solution pH to 3, there was a transition from vesicles to micelles. The same behavior, that is, transition from vesicles to micelles was also realizable on addition of β‐cyclodextrin (β‐CD) to the PEO‐b‐P(DEAEMA‐co‐PPHMA) solution at pH 8. Furthermore, after β‐CD was added, alternating irradiation of the solution with UV and visible light can also induce the reversible micelle‐to‐vesicle transition because of the photoinduced trans‐to‐cis isomerization of azobenzene units. The multistimuli‐responsive precise morphological changes were studied by laser light scattering, transmission electron microscopy, and UV–vis spectra. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Poly(9‐undecyl‐9‐methyl‐fluorene) and poly(9‐pentadecyl‐9‐methyl‐fluorene): Synthesis,solution structure,and effect of side chain asymmetry on aggregation behavior

We report on solution aggregates and backbone conformation of poly(9‐undecyl‐9‐methyl‐fluorene) (PF1‐11) and poly(9‐pentadecyl‐9‐methyl‐fluorene) (PF1‐15), having two different side chains compared with poly(9,9‐dihexylfluorene) (PF6) and poly(9,9‐dioctylfluorene) (PF8) with two identical side chains. In the poor solvent methylcyclohexane (MCH), X‐ray scattering indicates that PF1‐11 and PF1‐15 appear as three‐dimensional aggregates (5–10 nm wide and thick), forming ribbon‐like agglomerates (correlation lengths of 100 nm). PF6 and PF8 appear as two‐dimensional aggregates (>10 nm wide and 2–3 nm thick) involving ribbon‐like agglomerates (correlation lengths much greater than 100 nm). Upon heating, all aggregates undergo a gel–sol transition which occurs at lower temperatures for PF1‐11 and PF1‐15 (<60°C) than for PF6 and PF8 (>80°C). In the good solvent toluene, PF1‐11 and PF1‐15 form networks of cylindrical particles. The mesh size and the cylinder radius are smaller in 24°C toluene (60 nm, 0.5 nm) than in 60°C MCH (300 nm, 1–2 nm). Nuclear magnetic resonance spectra in toluene‐d₈ together with density functional theory calculations suggest higher torsion angles between polymer repeat units for PF6, PF8, and PF1‐11 (less planar conformation) and a gauche arrangement of the dihedral angles between the bridge carbon atom and the side chain methylene groups in PF1‐15. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 826–837     

Silole‐containing poly(silylenevinylene)s: Synthesis,characterization, aggregation‐enhanced emission,and explosive detection

Hydrosilylation polymerizations of 1,1‐dimethyl‐2,5‐bis(4‐ethynylphenyl)‐3,4‐diphenylsilole with aromatic silylhydrides including 1,4‐bis(dimethylsilyl)benzene, 4,4′‐bis(dimethylsilyl)biphenyl, 2,5‐bis(dimethylsilyl)thiophene, and 2,7‐bis(dimethylsilyl)‐9,9‐dihexylfluorene in the presence of Rh(PPh₃)₃Cl catalyst in refluxed tetrahydrofuran afford a series of silole‐containing poly(silylenevinylene)s. Under optimum condition, the alkyne polyhydrosilylation reactions progress efficiently and regioselectively, yielding polymers with high molecular weights (M_w up to 95,300) and good stereoregularity (E content close to 99%) in high yields (up to 92%). The polymers are processable and thermally stable, with high decomposition temperatures in the range of 420?449 °C corresponding to 5% weight loss. They are weakly fluorescent in the solution state but become emissive in the aggregate and film states, demonstrating their aggregation‐enhanced emission characteristics. The explosive sensing capabilities of the polymers are examined in both solution and aggregate states. The emissions of the polymers aggregates in aqueous mixture are quenched more efficiently by picric acid in an exponential pattern with high quenching constants (up to 27,949 L mol^?1), suggesting that the polymers aggregates are sensitive chemosensors for explosive detection. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of pH sensitive poly(glycidol)‐b‐poly(4‐vinylpyridine) block copolymers

Block copolymers of poly(glycidol)‐b‐poly(4‐vinylpyridine) were obtained by ATRP of 4‐vinylpyridine initiated by ω‐(2‐chloropropionyl) poly(glycidol) macroinitiators. By changing the monomer/macroinitiator ratio in the synthesis polymers with varied P4VP/PGl molar ratio were obtained. The obtained block copolymers showed pH sensitive solubility. It was found that the linkage of a hydrophilic poly(glycidol) block to a P4VP influenced the pK_a value of P4VP. DLS measurements showed the formation of fully collapsed aggregates exceeding pH 4.7. Above this pH values the collapsed P4VP core of the aggregates was stabilized by a surrounding hydrophilic poly(glycidol) corona. The size of the aggregates depended significantly upon the composition of the block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1782–1794, 2009     

Click chemistry‐based synthesis of azo polymers for second‐order nonlinear optics

Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second‐order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (T_g) in the range of 120–140 °C. The molecular weights (M_w) of these polymers (measured by gel permeation chromatography) were in the range 37,900–55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV–vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polyelectrolyte‐Assisted Noncovalent Functionalization of Carbon Nanotubes with Ordered Self‐Assemblies of a Water‐Soluble Porphyrin

The self‐assembly and induced supramolecular chirality of meso‐tetrakis(4‐sulfonatophenyl)porphyrin (TSPP) on both single‐wall (SWCNT) and multiwall carbon nanotubes (MWCNT) are investigated. Under mild pH conditions (pH 3), TSPP forms aggregates when CNTs are dispersed in an aqueous solution containing positively charged polyelectrolytes such as poly‐L ‐lysine (PLL) or poly(allylamine hydrochloride) (PAH). Evidence for the geometry of the porphyrin aggregates is obtained from absorption spectra, whereby the fingerprints of J‐ and H‐aggregates are clearly seen only in the presence of smaller‐diameter nanotubes. J‐aggregates are better stabilized with PLL, whereas in the presence of PAH mainly H‐aggregates prevail. Excited‐state interactions within these nanohybrids are studied by steady‐state and time‐resolved fluorescence. The porphyrin emission intensity in the nanohybrid solution is significantly quenched compared to that of TSPP alone, and this implies strong electronic interaction between CNTs and porphyrin molecules. Fluorescence lifetime imaging microscopy (FLIM) further supports that porphyrin arrays are associated with the MWCNT sidewalls wrapped in PLL. In the case of the SWCNT hybrid, spherical structures associated with longer fluorescence lifetime appeared after one week, indicative of H‐aggregates of TSPP. The latter are the result of π–π stacking of porphyrin units on neighboring nanotubes facilitated by the strong tendency of these nanotubes to interact with each other. These results highlight the importance of optimum dimensions and surface‐area architectures of CNTs in the control/stability of the porphyrin aggregates with promising properties for light harvesting.     

Fibrillar structure of self‐assemblies formed from heterocomplementary monomers linked through sextuple hydrogen‐bonding arrays

The nanostructure of the fibrillar supramolecular aggregates generated in decane solutions of homoditopic heterocomplementary monomers forming sextuple hydrogen‐bond‐mediated self‐assemblies was investigated by small‐angle neutron scattering and cryogenic‐temperature transmission electron microscopy. The persistence length (L_p) of the fibrillar aggregates was found to be ～18 nm, as inferred from combined measurements of the radius of gyration and of the contour length. The values of both the weight‐average molecular weight and the mass per unit length of the fibers suggest that the latter consist of few aggregated monomolecular wires. At T = 25 °C, the formation of branched aggregates occurs around the crossover concentration, C*, between the dilute and semidilute regimes, whereas the classical behavior of equilibrium polymers is observed at T = 65 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 103–115, 2007     

Intramolecular Charge Interactions as a Tool to Control the Coiled‐Coil‐to‐Amyloid Transformation

Under the influence of a changed environment, amyloid‐forming proteins partially unfold and assemble into insoluble β‐sheet rich fibrils. Molecular‐level characterization of these assembly processes has been proven to be very challenging, and for this reason several simplified model systems have been developed over recent years. Herein, we present a series of three de novo designed model peptides that adopt different conformations and aggregate morphologies depending on concentration, pH value, and ionic strength. The design strictly follows the characteristic heptad repeat of the α‐helical coiled‐coil structural motif. In all peptides, three valine residues, known to prefer the β‐sheet conformation, have been incorporated at the solvent‐exposed b, c, and f positions to make the system prone to amyloid formation. Additionally, pH‐controllable intramolecular electrostatic repulsions between equally charged lysine (peptide A) or glutamate (peptide B) residues were introduced along one side of the helical cylinder. The conformational behavior was monitored by circular dichroism spectroscopic analysis and thioflavin T fluorescence, and the resulting aggregates were further characterized by transmission electron microscopy. Whereas uninterrupted α‐helical aggregates are found at neutral pH, Coulomb repulsions between lysine residues in peptide A destabilize the helical conformation at acidic pH values and trigger an assembly into amyloid‐like fibrils. Peptide B features a glutamate‐based switch functionality and exhibits opposite pH‐dependent folding behavior. In this case, α‐helical aggregates are found under acidic conditions, whereas amyloids are formed at neutral pH. To further validate the pH switch concept, peptide C was designed by including serine residues, thus resulting in an equal distribution of charged residues. Surprisingly, amyloid formation is observed at all pH values investigated for peptide C. The results of further investigations into the effect of different salts, however, strongly support the crucial role of intramolecular charge repulsions in the model system presented herein.     

Temperature‐Induced Transformation from Large Compound Vesicles to Worm‐like Aggregates by ABC Triblock Copolymer

Two triblock polymers, tetraaniline‐block‐poly(N‐isopropyl acrylamide)‐block‐poly(hydroxyethyl acrylate) (TA‐b‐PNIPAM‐b‐PHEA) and TA‐b‐PHEA‐b‐PNIPAM, were synthesized with unambiguous structure by a two step method. The difference of these two diblock polymers is the connection order of carboxyl group to block, e.g., carboxyl group to PNIPAM block for PNIPAM‐b‐PHEA and to PHEA block for PHEA‐b‐PNIPAM. Secondly, block tetraaniline was linked to the diblock polymer through amidation to yield the corresponding triblock copolymer. Both of them have almost the identical chemical compositions. The only difference is the connection order of each block in the triblock polymers. When they were self‐assembled at 45°C in a suitable solution, both of their aggregates have spherical shape with slight defects on their surface with the average diameter of about 400 nm. However, when their aggregate dispersion was cooled down to 20°C, only TA‐b‐PHEA‐b‐PNIPAM's morphology changed, forming worm‐like aggregates with the diameter of about 100–200 nm transformed from spherical aggregates. Both amphiphilic property and position of each block in this triblock copolymer are very essential for this morphology transformation. Since the worm‐like aggregates presented here by our group have hollow structure inside, its controlled release properties for doxorubicin were evaluated. Drug release experiment indicated that along with the temperature changes, the rearrangement of the intermediate layer structure caused morphology change in aggregate, thus accelerating the speed of drug release.     

Glycopolymeric inhibitors of β‐glucuronidase I. Synthesis and polymerization of styrene derivatives having pendant D‐glucaric moieties

Two kinds of novel vinyl monomers having D ‐glucaric moieties leading to a new type of glycopolymeric inhibitors of β‐glucuronidase, N‐p‐vinylbenzyl‐6‐D ‐glucaramide (6 ) and potassium N‐p‐vinylbenzyl‐6‐D ‐glucaramid‐1‐ate (8 ), were synthesized by the reaction of D ‐glucaro‐6,3‐lactone (3 ) with p‐vinylbenzylamine (5 ) with no catalyst, and the subsequent treatment of the reaction mixture with acetic anhydride and potassium hydroxide aqueous solution, respectively. The radical copolymerization of 8 with acrylamide in various feed ratios at 60°C in 0.1 N potassium chloride aqueous solution gave water‐soluble copolymers (9 ) composed of a synthetic polymeric main chain and many pendant D ‐glucaric chains. The resulting glycopolymers (9 ) were found to inhibit the activity of β‐glucuronidase strongly through a model reaction with p‐nitrophenyl β‐D ‐glucuronide (10 ) in acetic buffer solution (pH 4.7). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 303–312, 1999     

Amino‐Acid‐Based Zwitterionic Polymer and Its Cu(II)‐Induced Aggregation into Nanostructures: A Template for CuS and CuO Nanoparticles

A convenient and water‐based approach is described for the synthesis of an l ‐lysine‐based zwitterionic polymer, poly(ε−l ‐lysinyl acrylamide) (PLAM), without using protecting group chemistry, chromatographic purifications, and organic solvents as the reaction media. PLAM contains both amine and carboxylic acid groups in each repeating unit, which can either be protonated or deprotonated just by altering the pH of the solution to obtain overall positive or negative charge. PLAM is tested for its applicability as a zwitterionic polymeric buffer in water. Cu(II) ion‐induced aggregation of PLAM as a function of solution pH is studied. Spherical nanogel aggregates are formed at pH 9.5 due to aggregation of PLAM through its complexation with Cu(II) ion. Spherical aggregates appear to dissociate via breaking of the complexation at a pH < 5.5 resulting in molecular dissolution of PLAM. This aggregation process is pH reversible. The Cu(II)–PLAM aggregates are used as a template for fabrication of CuO and CuS nanoparticles.

     

Responsive Thiolactone‐Derived N‐Substituted Poly(Urethane‐Amide)s

AB′ type monomers containing a thiolactone unit and vinyl ether moiety have been prepared with high yields. Aminolysis of the thiolactone moiety generates the corresponding thiol in situ, and upon UV‐irradiation, radical polyaddition occurs in the same medium, yielding linear poly(amide‐urethane)s with different side chain residues and (Poly(Ethylene Oxide)) PEO‐like backbone. Moreover, these unique polymers feature lower critical solution temperature behavior in water. Systematic modification of the responsive polymers reveals the influence of the variation of the side chains and the backbone structure on the corresponding solubility properties. In selected cases, multiresponsive polymers have been developed, which also respond to pH and metal concentration.

     

Stepped association of comb‐like and stimuli‐responsive graft chitosan copolymer synthesized using ATRP and active ester conjugation methods

Herein, we report the synthesis of a comb‐like pH‐sensitive graft copolymer, poly[(2‐dimethylamino)ethyl methacrylate]‐graft‐chitosan, using atom transfer radical polymerization (ATRP) and active ester conjugation methods. The utilization of ATRP guaranteed the narrow molecular weight distribution of the side chains, which further led to the low polydispersity of the copolymer aggregates. The active ester reaction took place in the mild and homogeneous solutions, and the graft ratio reached 58%. The pH‐responsive association behavior of the graft copolymer in aqueous solution was examined by potentiometric titration, laser light scattering, surface tensiometry, and transmission electron microscopy. Because of the difference in proton dissociation between the amine groups of chitosan and DMAEMA segments, the copolymer exhibited the different conformations with pH variation: random coils at pH ∼ 4, core‐shell structured micelles at pH 5–6, double‐layered hard spheres at pH ∼ 7, and larger aggregates at pH ∼ 8. The beneath mechanism cause the microstructure changes as a function of pH was discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6682–6692, 2009     

Synthesis of backbone thermo and pH dual‐responsive hyperbranched poly(amine‐ether)s through proton‐transfer polymerization

Stimuli‐responsive hyperbranched polymers have attracted great attention in recent years because of their wide applications in biomedicine. Through proton‐transfer polymerization of triethanolamine and 1,2,7,8‐diepoxyoctane with the help of potassium hydride, a series of novel backbone thermo and pH dual‐responsive hyperbranched poly(amine‐ether)s were prepared successfully in one‐pot. The degrees of branching of the resulting polymers were at 0.40–0.49. Turbidity measurements revealed that hyperbranched poly(amine‐ether)s exhibited thermo and pH dual‐responsive properties in water. Importantly, these responsivities could be readily adjusted by changing the polymer composition as well as the polymer concentration in aqueous solution. Moreover, in vitro evaluation demonstrated that hyperbranched poly(amine‐ether)s showed low cytotoxicity and efficient cell internalization against NIH 3T3 cell lines. These results suggest that these backbone thermo and pH dual‐responsive hyperbranched poly(amine‐ether)s are promising materials for biomedicine. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Acid‐labile,thermoresponsive (meth)acrylamide polymers with pendant cyclic acetal moieties

Acid‐labile, thermoresponsive polymers with pendant six‐membered cyclic acetal groups were prepared by radical polymerization of two monomers, N‐(2,2‐dimethyl‐1,3‐dioxan‐5‐yl) methacrylamide (NDMM) and N‐(2,2‐dimethyl‐1,3‐dioxan‐5‐yl) acrylamide (NDMA). The aqueous solution properties of the polymers, PNDMM and PNDMA, were studied by turbidimetry, ¹H NMR, fluorescence, and DSC measurements. It is found that both polymers show sensitive and reversible phase transitions with distinct lower critical solution temperatures (LCST). Below their LCSTs, there are still some polymer aggregates as evidenced by measurements of pyrene excitation spectra and urea effects on the cloud points (CP) of polymers. The salting effect of six inorganic sodium salts on the phase transition behavior of PNDMM was investigated by turbidimetric approach. The salting‐out to salting‐in effect is in the order of SO₄^2? > F^? > Cl^? > Br^? > I^? > SCN^?, following the Hofmeister's series. pH‐dependent hydrolysis of PNDMM and PNDMA was studied by turbidimetric and ¹H NMR methods. They are both pH‐sensitive and their hydrolysis rates significantly increase with decreasing pH value. The CP of PNDMM gradually increases with the acid‐triggered hydrolysis of the acetal groups and the hydrolyzed polymer with ～ 30% hydrolysis degree does not show thermally induced phase transition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4332–4343, 2008     

Ordered Solid‐State Microstructures of Conjugated Polymers Arising from Solution‐State Aggregation

Controlling the solution‐state aggregation of conjugated polymers for producing specific microstructures remains challenging. Herein, a practical approach is developed to finely tune the solid‐state microstructures through temperature‐controlled solution‐state aggregation and polymer crystallization. High temperature generates significant conformation fluctuation of conjugated backbones in solution, which facilitates the polymer crystallization from solvated aggregates to orderly packed structures. The polymer films deposited at high temperatures exhibit less structural disorders and higher electron mobilities (up to two orders of magnitude) in field‐effect transistors, compared to those deposited at low temperatures. This work provides an effective strategy to tune the solution‐state aggregation to reveal the relationship between solution‐state aggregation and solid‐state microstructures of conjugated polymers.     

Thermal and optical properties of some phosphorus‐containing poly(1,3,4‐oxadiazole‐ester‐imide)s

A series of phosphorus‐containing poly(1,3,4‐oxadiazole‐ester‐imide)s was prepared by polycondensation reaction of an aromatic dianhydride, namely 1,4‐[2‐(6‐oxido‐6H‐dibenz<c,e><1,2>oxaphosphorin‐6‐yl)]‐naphthalene‐bis(trimellitate)dianhydride, with different aromatic diamines containing 1,3,4‐oxadiazole ring. A solution imidization procedure was used to convert quantitatively the poly(amic acid) intermediates to the corresponding polyimides. The chemical structures of the monomers and polymers were confirmed by Fourier transform infrared, ¹H NMR and ³¹P NMR spectroscopy. The polymers were easily soluble in polar solvents such as N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylformamide and tetrahydrofuran. They exhibited good thermal properties having the decomposition temperature above 380°C and the glass transition temperature in the range of 201–232°C. Due to the presence of phosphorus the polymers gave high char yield in termogravimetric analysis, hence good flame retardant properties. Optical properties were analyzed in solution by using UV–vis and photoluminescence spectroscopy. Solutions of the polymers in NMP exhibited photoluminescence in the blue region. Copyright © 2010 John Wiley & Sons, Ltd.     

Unusual Stepwise Protonation and J‐Aggregation of meso‐Tetrakis(N‐methylpyridinium‐4‐yl)porphine on Binding Poly(sodium vinylsulfonate)

The binding of a tetracationic porphyrin to a highly charged polymer like poly(sodium vinylsulfonate) has been investigated over a wide pH range and under various experimental conditions. We present evidence that, depending on the pH, the high electrostatic field exerted by the polymer stabilizes the diprotonated form of the free base porphyrin at unusual pH values or otherwise causes the formation of H‐type aggregates. In particular, at a low polymer concentration, lowering the pH at first allows the formation of the diacid species then it determines its reorganization in close‐packed J‐type aggregates. The employment of various metallo‐derivatives of the title porphyrin enables a better insight into the nature of all the detected species.