Sanjib K. Patra

Cylindrical Micelles of Controlled Length with a π-Conjugated Polythiophene Core via Crystallization-Driven Self-Assembly

Solution self-assembly of the regioregular polythiophene-based block copolymer poly(3-hexylthiophene)-b-poly(dimethylsiloxane) yields cylindrical micelles with a crystalline P3HT core. Monodisperse nanocylinders of controlled length have been prepared via crystallization-driven self-assembly using seed micelles as initiators.

Main‐Chain Heterobimetallic Block Copolymers: Synthesis and Self‐Assembly of Polyferrocenylsilane‐b‐Poly(cobaltoceniumethylene)

Two metals are better than one: Main-chain heterometallic block copolymers composed of iron- and cobalt-rich blocks (see picture) were synthesized through consecutive photocontrolled ring-opening polymerization (ROP) of sila[1]ferrocenophanes and dicarba[2]cobaltocenophanes followed by oxidation of the cobaltocene-containing block. The redox properties and self-assembly of the resulting block copolymers in solution were also studied.

Dimensional Control of Block Copolymer Nanofibers with a π-Conjugated Core: Crystallization-Driven Solution Self-Assembly of Amphiphilic Poly(3-hexylthiophene)-b-poly(2-vinylpyridine)

With the aim of accessing colloidally stable, fiberlike, π-conjugated nanostructures of controlled length, we have studied the solution self-assembly of two asymmetric crystalline-coil, regioregular poly(3-hexylthiophene)-b-poly(2-vinylpyridine) (P3HT-b-P2VP) diblock copolymers, P3HT23-b-P2VP115 (block ratio=1:5) and P3HT44-b-P2VP115 (block ratio=ca. 1:3). The self-assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu-catalyzed azide-alkyne cycloaddition reactions of azide-terminated P2VP and alkyne end-functionalized P3HT homopolymers. When the block copolymers were self-assembled in a solution of a 50% (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP-selective alcoholic solvent (MeOH3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain-extended P3HT blocks. The crystallinity and π-conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide-angle X-ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT23-b-P2VP115 resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT23-b-P2VP115 unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L(w)/L(n) < 1.11) and lengths from about 100-300 nm, that were dependent on the unimer-to-seed micelle ratio.

Photocontrolled Living Anionic Polymerization of Phosphorus-Bridged [1]Ferrocenophanes: A Route to Well-Defined Polyferrocenylphosphine (PFP) Homopolymers and Block Copolymers

Phosphorus-bridged strained [1]ferrocenophanes [Fe{(eta-C(5)H(4))(2)P(CH(2)CMe(3))}] (2) and [Fe{(eta-C(5)H(4))(2)P(CH(2)SiMe(3))}] (3) with neopentyl and (trimethylsilyl)methyl substituents on phosphorus, respectively, have been synthesized and characterized. Photocontrolled living anionic ring-opening polymerization (ROP) of the known phosphorus-bridged [1]ferrocenophane [Fe{(eta-C(5)H(4))(2)P(CMe(3))}] (1) and the new monomers 2 and 3, initiated by Na[C(5)H(5)] in THF at 5 degrees C, yielded well-defined polyferrocenylphosphines (PFPs), [Fe{(eta-C(5)H(4))(2)PR}](n) (R=CMe(3) (4), CH(2)CMe(3) (5), and CH(2)SiMe(3) (6)), with controlled molecular weights (up to ca. 60 x 10(3) Da) and narrow molecular weight distributions. The PFPs 4-6 were characterized by multinuclear NMR spectroscopy, DSC, and by GPC analysis of the corresponding poly(ferrocenylphosphine sulfides) obtained by sulfurization of the phosphorus(III) centers. The living nature of the photocontrolled anionic ROP allowed the synthesis of well-defined all-organometallic PFP-b-PFS(F) (7a and 7b) (PFS(F)=polyferrocenylmethyl(3,3,3,-trifluoropropyl)silane) diblock copolymers through sequential monomer addition. TEM studies of the thin films of the diblock copolymer 7b showed microphase separation to form cylindrical PFS(F) domains in a PFP matrix.

Role of axial donors in the ligand isomerization processes of quadruply bonded dimolybdenum(II) compounds.

Quadruply bonded dimolybdenum(II) complexes with NP-R (2-(2-R)-1,8-naphthyridine; R = thiazolyl (NP-tz), furyl (NP-fu), thienyl (NP-th)) and 2,3-dimethyl-1,8-naphthyridine (NP-Me 2) have been synthesized by reactions of cis-[Mo2(OAc)2(CH3CN)6][BF4]2 with the corresponding ligands. The products cis-[Mo2(NP-tz)2(OAc)2][BF4]2 (1), trans-[Mo2(NP-fu)2(OAc)2][BF4]2 (2), trans-[Mo2(NP-th)2(OAc)2][BF4]2 (3), and trans-[Mo2(NP-Me2)2(OAc)2][BF4]2 (4) were isolated and characterized. The NP-R ligands with stronger R = pyridyl and thiazolyl donors result in cis isomers whereas the weaker furyl and thienyl appendages lead to compounds having a trans orientation of the ligands. The use of NP-Me2 leads to a trans structure with a tetrafluoroborate anion occupying one of the axial sites. Complete replacement of two acetate groups by acetonitrile in 1 and 2 resulted in the cis isomers [Mo2(NP-tz)2(CH3CN)4][OTf]4 (5) and [Mo2(NP-fu)2(CH3CN)4][OTf]4 (6) respectively. The combination of one acetate and two acetonitriles as ancillary ligands, however, yields trans-[Mo2(NP-tz)2(OAc)(CH3CN)2][BF4]3 (7) in the solid state as determined by X-ray crystallography. (1)H NMR spectra of the products are diagnostic of the cis and trans dispositions of the ligands. Solution studies reveal that the ligand arrangements observed in the solid state are mostly retained in the acetonitrile medium. The only exception is 7, for which a mixture of cis and trans isomers are detected on the NMR time scale. The isolation of trans compounds 2- 4 from the cis precursor [Mo2(OAc)2(CH3CN)6][BF4]2 indicates that an isomerization process occurs during the reactions. The mechanism involving acetate migration through axial coordination has been invoked to rationalize the product formation. Compounds 1- 7 were structurally characterized by single-crystal X-ray methods.

Tetragonal and Helical Morphologies from Polyferrocenylsilane Block Polyelectrolytes via Ionic Self-Assembly

The use of ionic self-assembly, a facile non-covalent approach, to access non-conventional block copolymer morphologies, including tetragonal and helical structures, from a combination of polyferrocenylsilane diblock copolymer polyelectrolytes and AOT-based surfactants, is described.

Responsive vesicles from the self-assembly of crystalline-coil polyferrocenylsilane-block-poly(ethylene oxide) star-block copolymers.

We demonstrate the synthesis and characterization of star-shaped crystalline-coil block copolymers with four arms consisting of an inner block of poly(ethylene oxide) and an outer semicrystalline compartment of poly(ferrocenyldimethylsilane), [PEO(50) -b-PFDMS(35)](4). The materials were synthesized by transition-metal-catalyzed ring-opening polymerization of dimethylsila[1]ferrocenophane in the presence of silane-functionalized four-arm PEO stars as macroinitiators and they exhibited a moderate polydispersity (PDI≅1.4). Self-assembly in mixtures of THF and different alcohols as selective solvents for the PEO block resulted in the formation of semicrystalline vesicles (ethanol, 1-butanol) or large, rather ill-defined, spherical structures (methanol). Further, both the rate of addition of the selective co-solvent and the overall solvent/non-solvent ratio drastically affected the size and stability of the self-assembled particles. We could also show that a photoacid generator, as a model for an active substance, can be encapsulated and the UV-induced generation of HCl resulted in a straightforward degradation of the organometallic vesicles.

Organic-metalloblock copolymers via photocontrolled living anionic ring-opening polymerization

A new method for the preparation of organic-organometallic diblock copolymers including a polyferrocenylsilane (PFS) metalloblock through photocontrolled ring-opening polymerization (ROP) is reported. Polystyrene (PS) homopolymers end-capped with a cyclopentadienyl group (1) were used as macroinitiators for the photocontrolled ROP of sila[1]ferrocenophanes [Fe(η-C5H4)2Si{C≡CtBu}2] 3a and [Fe(η-C5H4)2Si(Me)(C≡CSiMe3)] 3b to afford diblock copolymers with controlled molecular weights and block ratios, as well as low polydispersities (PDI < 1.2). Block copolymer PSm-b-[Fe(η-C5H4)2Si{C≡C(t-Bu)}2]n4 was clusterized with [Co2(CO)8], forming the highly metallized PSm-b-[Fe(η-C5H4)2Si{Co2(CO)6C2(t-Bu)}2]n (PS-bb-(Co-PFS), 7). The diblock PSm-b-[Fe(η-C5H4)2Si(Me)(C≡CH)]n6 was prepared by selective desilylation of PSm-b-[Fe(η-C5H4)2Si(Me)(C≡CSiMe3)]n5 was then reacted with ClAuP(n-Bu)3 in the presence of an amine as HCl acceptor to afford PSm-b-[Fe(η-C5H4)2Si(Me){C≡CAuP(n-Bu)3}]n (PS-bbb-(Au-PFS), 8). Preliminary studies on the self-assembly of these materials in thin films showed phase separation with metal-rich nanodomains within an organic matrix.

Benzodithieno-imidazole based π-conjugated fluorescent polymer probe for selective sensing of Cu2+

π-Conjugated polymers appended with binding sites are of considerable interest as an evolving new class of heavy and toxic metal ion sensors through fluorescence quenching. In this study we describe the synthesis and characterization of a p-bromophenyl substituted benzodithieno-imidazole based soluble and rigid π-conjugated polymer with N and S donors exhibiting outstanding sensitivity towards Cu2+ by emission quenching through photoinduced electron transfer (PET). Detailed photophysical and ion sensing studies have been demonstrated to understand insight of the polymer–metal ion interaction which is responsible for selective fluorescence quenching. The corresponding polymer is also explored as a thin-film polymeric sensor towards Cu2+ as monitored by a photoluminescence study.

Arylene–vinylene terpyridine conjugates: highly sensitive, reusable and simple fluorescent probes for the detection of nitroaromatics

A series of highly emissive arylene–vinylene conjugated 4′-(4-{2-[aryl]-ethenyl}phenyl)-2,2′:6′,2′′-terpyridines (aryl = 4-methylphenyl, 4-fluorophenyl, 1-naphthyl, and 9-anthralyl in P1–P4 respectively) have been explored for the detection of nitroaromatic compounds (NACs). The synthesized push–pull fluorescent probes show remarkable sensitivity toward NACs in solution, vapor and contact mode as ‘turn-off’ sensors which can be visualized by the naked eye. The photophysical studies reveal that electron transfer occurs from the electron rich arylene–vinylene conjugated terpyridines to the electron-deficient NACs through supramolecular complexation which is further illustrated by the time-resolved fluorescence and 1H NMR titration experiment. The arylene–vinylene conjugated terpyridines offer excellent sensitivity toward picric acid (PA) exhibiting nanomolar detection in contact mode, and ppm level detection in the solution state with association constants in the range of 2.54–8.08 × 104 M−1. The HOMO–LUMO energy levels have been calculated from the electrochemical and TDDFT studies to understand the efficacy and the mechanism of electron transfer from the probe to the NACs leading to fluorescence quenching. The reversibility, recyclability and contact mode detection of PA at a nanomolar level demonstrates the practical utility of the probes as a solid state kit for the onsite detection of NAC explosives.