Cooperative supramolecular polymerization of a perylene diimide derivative and its impact on electron-transporting properties.

H-bonding-promoted supramolecular polymerization of a perylene diimide (PDI) building block and its impact on charge carrier mobility were studied. PDI-1, containing a carboxylic acid group, exhibits H-aggregation in a non-polar solvent decalin while in THF or chloroform it remains in the monomeric form. In contrast, the control molecule PDI-2, containing an ester group does not show aggregation even in decalin, indicating that H-bonding among the carboxylic acid is primarily responsible for H-aggregation, which is further verified by the FT-IR study. A variable temperature UV/Vis study establishes a cooperative pathway for the supramolecular polymerization of PDI-1. Microscopy images show a short fibrillar morphology. Flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements reveal significantly higher electrical conductivity for the PDI-1 film prepared from decalin compared with that prepared from THF/MeOH or the film of non-aggregated PDI-2 prepared from decalin. By combining the transient absorption spectroscopy data (that estimate the charge carrier generation efficiency) and the TRMC evaluated conductivity, the 1D charge carrier mobility of PDI-1 (µe,1D) is estimated to be 0.24 cm2 V-1 s-1, which is among the top values reported for any PDI derivative measured using the same technique.

Extended supramolecular organization of π-systems using yet unexplored simultaneous intra- and inter-molecular H-bonding motifs of 1,3-dihydroxy derivatives.

Unique H-bonding motifs of 1,3-dihydroxyl derivatives involving simultaneous intra- and inter-molecular H-bonding results in extended organization of pendant chromophores with a spatial distance suitable for π-π interaction. A preformed assembly with appended acceptor units exhibits host-guest interaction with specific donors by charge-transfer complex formation.

Macromol. Rapid commun. 15/2014.

Back Cover: An efficient polycondensation route for telechelic poly(disulfide)s is developed from two monomers-2,2'-dithiodipyridine and 1,6-hexanedithiol-using stoichiometric imbalance between them. Selective thiol-disulfide exchange of the two terminal pyridyl disulfide groups with functional thiol produces functionalized poly(disulfide)s that can be used as a macro-initiator to initiate ROP of lactide generating a triblock copolymer with degradable middle block. Further details can be found in the article by D. Basak, R. Kumar, and S. Ghosh* on page 1340.

Telechelic Poly(disulfide)s and Related Block Copolymer.

In this communication, a mild, efficient, and generalized polycondensation route is developed for poly(disulfide)s from commercially available monomers 2,2'-dithiodipyridine and 1,6-hexanedithiol. Using the stoichiometric imbalance between the two monomers, it is possible to produce telechelic poly(disulfide)s of predictable molecular weight with reactive pyridyl disulfide groups at both the terminals of the chain. The two terminal pyridyl disulfide groups can be quantitatively replaced by a functional thiol using selective thiol-disulfide exchange and thus produces functional telechelic poly(disulfide)s, which can be used as a macroinitiator to initiate ring-opening poly-merization of a cyclic lactide monomer generating an ABA-type triblock copolymer with degradable B block.

pH-Regulated Controlled Swelling and Sustained Release from the Core Functionalized Amphiphilic Block Copolymer Micelle.

pH-responsive amphiphilic block copolymers based on poly(ethylene glycol)monomethyl ether-b-poly(methyl methacrylate-co-methacrylamidepropanoic acid) (PEO-b-PMMA-co-PMAPA) with different MMA/MAPA ratios were synthesized from respective amine-reactive prepolymers based on poly(ethylene glycol)monomethyl ether-b-poly(methyl methacrylate-co-methacryloxysuccinimide) (PEO-b-PMMA-co-PMASI) in such a way that the pH-responsive carboxylic acid groups were randomly distributed in the hydrophobic (PMMA) block. In aqueous medium, they formed micellar aggregates. Control experiments showed stability and critical aggregation concentration and dye encapsulation properties were better for carboxylic acid functionalized micelles at acidic pH compared to a structurally similar block copolymer micelle that lacked any carboxylic acid group. This was attributed to H-bonding among the carboxylic acid groups. In basic pH upon deprotonation, controlled swelling of the aggregates was observed due to repulsion among the negatively charged carboxylate groups. The extent of swelling/deswelling was well controlled by simply changing the percentage of the pH-responsive units in the hydrophobic block and could be probed quantitatively by pH-dependent dynamic light scattering (DLS) and fluorescence resonance energy transfer (FRET) studies. The aggregates were able to encapsulate a hydrophobic guest such as pyrene at the interior of the micelle, and sustained release of this hydrophobic probe was achieved selectively at basic pH due to swelling of the micelles instead of complete disassembly that generally leads to burst release.

Anhydrous proton conductivities of squaric acid derivatives.

In this communication, we introduce squaric acid derivatives as anhydrous proton conductors. We report the synthesis, characterization and proton conductivities of four squaric acid derivatives. The anhydrous proton conductivity of one of the derivatives was 2.3 × 10(-3) S cm(-1) at 110 °C, comparable to the conductivity of molten 1H-1,2,3-triazole or 1H-imidazole.

Modeling energy landscapes of proton motion in nonaqueous, tethered proton wires.

We have modeled structures and energetics of anhydrous proton-conducting wires: tethered hydrogen-bonded chains of the form ···HX···HX···HX···, with functional groups HX = imidazole, triazole, and formamidine; formic, sulfonic, and phosphonic acids. We have applied density functional theory (DFT) to model proton wires up to 19 units long, where each proton carrier is linked to an effective backbone to mimic polymer tethering. This approach allows the direct calculation of hydrogen bond strengths. The proton wires were found to be stabilized by strong hydrogen bonds (up to 50 kJ/mol) whose strength correlates with the proton affinity of HX [related to pK(b)(HX)] and not to pK(a)(HX) as is often assumed. Geometry optimizations and ab initio molecular dynamics near 400 K on imidazole-based proton wires both predict that adding a proton to the end of such wires causes the excess charge to embed into the interior segments of these wires. Proton translocation energy landscapes for imidazole-based wires are sensitive to the imidazole attachment point (head or feet) and to wire architecture (linear or interdigitated). Linear imidazole wires with head-attachment exhibit low barriers for intrawire proton motion, rivaling proton diffusion in liquid imidazole. Excess charge relaxation from the edge of wires is found to be dominated by long-range Grotthuss shuttling for distances as long as 42 Å, especially for interdigitated wires. For imidazole, we predict that proton translocation is controlled by the energetics of desorption from the proton wire, even for relatively long wires (600 imidazole units). Proton desorption energies show no correlation with functional group properties, suggesting that proton desorption is a collective process in proton wires.

Proton conduction in discotic mesogens.

In this communication, we show that liquid crystalline phases lower the activation energy barrier for proton transport. The liquid crystalline phases were obtained using a triphenylene core with alkyl chains bearing a triazole moiety at their termini.

Single-molecule chiroptical spectroscopy: Fluorescence excitation of individual helicene molecules in polymer-supported thin-films.

We present results of fluorescence excitation circular dichroism studies of the chiroptical response of single (bridged triarylamine) helicene molecules immobilized at a polymer interface. We extract directly dissymmetry parameters, and corresponding probability distributions, associated with the single-molecule fluorescence excitation associated with modulation of a circular polarized excitation field for three different excitation wavelengths (405, 440, 457 nm) showing circular dichroism in bulk films. The observed single molecule chiroptical response is anomalously large in comparison with the results of time-dependent density functional calculations, and the observed defocused emission patterns seem to indicate a higher multipole nature to the transition probed. Our results provide new insights into chiroptical properties of chiral fluorophores that are hidden under the extensive averaging associated with conventional chiroptical probes.