Andre J. Gesquiere

Ultrastable, Highly Luminescent Organic-Inorganic Perovskite-Polymer Composite Films

A simple yet general swelling-deswelling microencapsulation strategy has been developed to achieve well dispersed and intimately passivated crystalline organic-inorganic perovskites nanoparticles within polymer matrixes and results in a series of highly luminescent CH3 NH3 PbBr3 (MAPbBr3 )-polymer composite films with unprecedented water and thermal stabilities and superior color purity.

Homo‐ and Heterochiral Supramolecular Tapes from Achiral, Enantiopure, and Racemic Promesogenic Formamides: Expression of Molecular Chirality in Two and Three Dimensions

Enantiomorphous monolayers of enantiopure formamides form on a graphite surface, while the racemic compound does not undergo a spontaneous resolution under similar conditions. This difference in the two-dimensional behavior has been studied by scanning tunneling microscopy (see image of the racemate adsorbed on graphite). A study of the three-dimensional crystallization of the racemic formamide by X-ray crystallographic analysis also shows that it forms racemic tapes.

Near-infrared photoresponse sensitization of solvent additive processed poly(3-hexylthiophene)/fullerene solar cells by a low band gap polymer

With the aim of extending the photoresponse of the poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester photovoltaic system into the near-infrared region, a low band gap polymer poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]] was incorporated to make ternary blend solar cells. Solvent additive 1,8-diiodooctane (DIO) was applied to optimize the phase separation in a one-step active layer preparation. Devices fabricated with DIO additive demonstrate an improvement of device power conversion efficiency by 17%, which can be attributed to favorable microscopic structure of the ternary blend with 1:1:0.2 composition processed with DIO and extended absorption on the red side of the visible spectrum up to 900 nm.

Dynamics in Physisorbed Monolayers of 5-Alkoxy-isophthalic Acid Derivatives at the Liquid/Solid Interface Investigated by Scanning Tunneling Microscopy

Monolayers of isophthalic acid derivatives at the liquid/solid interface have been studied with scanning tunneling microscopy (STM). We have investigated the dynamics related to the phenomenon of solvent co-deposition, which was previously observed by our research group when using octan-1-ol or undecan-1-ol as solvents for 5-alkoxy-isophthalic acid derivatives. This solvent co-deposition has now been visualized in real-time (two frames per second) for the first time. Dynamics of individual molecules were investigated in mixtures of semi-fluorinated molecules with video-STM. The specific contrast arising from fluorine atoms in STM images allows us to use this functionality as a probe to analyze the data obtained for the mixtures under investigation. Upon imaging the same region of a monolayer for a period of time we observed that non-fluorinated molecules progressively substitute the fluorinated molecules. These findings illustrate the metastable equilibrium that exists at the liquid/solid interface, between the physisorbed molecules and the supernatant solution.

Caveolae-Mediated Endocytosis of Conjugated Polymer Nanoparticles

Understanding the cellular entry pathways of synthetic biomaterials is highly important to improve overall labeling and delivery efficiency. Herein, cellular entry mechanisms of conjugated polymer nanoparticles (CPNs) are presented. CPNs are intrinsic fluorescent materials used for various biological applications. While CPNs cause no toxicity, decreased CPN uptake is observed from cancer cells pretreated with genistein, which is an inhibitor of caveolae-mediated endocytosis (CvME). CvME is further confirmed by high co-localization with caveolin-1 proteins found in the caveolae and caveosomes. Excellent photophysical properties, non-toxicity, and non-destructive delivery pathways support that CPNs are promising multifunctional carriers minimizing degradation of contents during delivery.

Influence of Backbone Rigidness on Single Chain Conformation of Thiophene-Based Conjugated Polymers

Structural order of conjugated polymers at different length scales directs the optoelectronic properties of the corresponding materials; thus it is of critical importance to understand and control conjugated polymer morphology for successful application of these materials in organic optoelectronics. Herein, with the aim of probing the dependence of single chain folding properties on the chemical structure and rigidness of the polymer backbones, single molecule fluorescence spectroscopy was applied to four thiophene-based conjugated polymers. These include regioregular poly(3-hexylthiophene) (RR-P3HT), poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-14), poly(2,5-bis(3-tetradecylthiophen-2-yl)thiophene-2-yl)thiophen-2-ylthiazolo[5,4-d]thiazole) (PTzQT-12), and poly(3,3-didodecylquaterthiophene)] (PQT-12). Our previous work has shown that RR-P3HT and PBTTT-14 polymer chains fold in their nanostructures, whereas PQT-12 and PTzQT-12 do not fold in their nanostructures. At the single molecule level, it was found that RR-P3HT single chains almost exclusively fold into loosely and strongly aggregated conformations, analogous to the folding properties in nanostructures. PQT-12 displays significant chain folding as well, but only into loosely aggregated conformations, showing an absence of strongly aggregated polymer chains. PBTTT-14 exhibits a significant fraction of rigid polymer chain. The findings made for single molecules of PQT-12 and PBTTT-14 are thus in contrast with the observations made in their corresponding nanostructures. PTzQT-12 appears to be the most rigid and planar conjugated polymer of these four polymers. However, although the presumably nonfolding polymers PQT-12 and PTzQT-12 exhibit less folding than RR-P3HT, there is still a significant occurrence of chain folding for these polymers at the single molecule level. These results suggest that the folding properties of conjugated polymers can be influenced by the architecture of the polymer backbones; however, other factors such as intermolecular stacking interactions, solvent environment, and side chain interactions in corresponding materials should also be taken into account to predict conjugated polymer material morphology.

Charge trapping and storage by composite P3HT/PC60BM nanoparticles investigated by fluorescence-voltage/single particle spectroscopy.

Fluorescence-voltage/single particle spectroscopy (F-V/SPS) was employed to study exciton-hole polaron interactions and interfacial charge transfer processes for pure poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) and composite P3HT/PC(60)BM NPs in functioning hole-injection devices. F-V/SPS data collected on a particle-by-particle basis reveal an apparent bistability in the fluorescence-voltage modulation curves for composite NPs of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) that is absent for pure P3HT NPs. A pronounced deep trapping of free electrons photogenerated from the composite P3HT/PC(60)BM NPs at the NP/dielectric interface and hole trapping by fullerene anions in composite P3HT/PC(60)BM NPs under photoexcitation lies at the basis of this finding. The deep electron trapping effect reported here for composite conjugated polymer/fullerene NPs presents an opportunity for future application of these NPs in nanoscale memory and imaging devices.

Fluorescent composite tubes with pH-controlled shapes

Building additional functionality into self-assembled organic tubes is of great interest for materials and biological applications. Here we report the synthesis and characterization of fluorescent composite tubes in which in situ formed cadmium sulfide (CdS) nanoparticles are embedded in lithocholic acid (LCA) tube walls. The LCA/CdS composite tubes are characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) absorption spectroscopy, and confocal fluorescence microscopy. The reported data show that the fluorescence of the composite tubes stems from CdS nanoparticles with the cubic (zinc blende) crystal structure that are embedded in the tube walls. As the fluorescence of CdS nanocrystals is bright, easily distinguishable, and resistant to photobleaching, long-term fluorescence microscopy observation of these LCA tubes is feasible. In addition, the shape of the fluorescent composite tubes can be controlled by the pH of the aqueous solution in which the tubes are formed. At pH 9.5, the self-assembled composite tubes show a straight shape, while at pH 13.0 the self-assembled composite tubes coil into a left-handed helix. The fluorescent composite tubes with pH-controlled shapes are a promising system for a variety of materials and biological applications.

Effect of PCBM Concentration on Photoluminescence Properties of Composite MEH-PPV/PCBM Nanoparticles Investigated by a Franck–Condon Analysis of Single-Particle Emission Spectra

The emission of composite conjugated polymer (MEH-PPV)/fullerene (PCBM) nanoparticles is investigated by single particle spectroscopy (SPS), and changes in vibronic structure with nanoparticle composition are evaluated by means of a detailed Franck-Condon analysis. Consistent with previous reports we find that the emission spectra can be modeled as the superposition of two types of emitters, one with aggregate character and one with molecular character. Major findings from the fitting of the SPS data to a Franck-Condon model are that 1) the occurrence of each of the two types of emitters changes with nanoparticle composition to the point that no aggregate emitters are detected (at 50 wt% PCBM), 2) at the highest PCBM doping levels (75 wt% PCBM) aggregate emitters reappear due to nanoscale phase separation in the composite nanoparticles, 3) the molecular emitters show small Huang-Rhys factors that increase with PCBM doping, indicative of extensive delocalization and exciton migration that is reduced by the disorder introduced in the polymer material by PCBM doping and 4) the aggregate emitters show large Huang-Rhys factors, indicative of the localized nature of these energy trap sites, with a broad distribution of values of these Huang-Rhys factors. The latter observation suggests a broad heterogeneous distribution of aggregate morphologies in blended conducting polymer materials, which can be attributed to variations in polymer chain folding and stacking at the aggregate sites. The reported results obtained by the SPS approach show how blending conjugated polymers with fullerenes at various doping levels induces changes in interchain interactions and aggregate site density even at length scales below a few tens of nanometers that affect conjugated polymer material properties, an observation that has gone unnoticed in bulk studies of blended conjugated polymer films.

Conducting polymer nanoparticles for targeted cancer therapy

First and second generation photosensitizers used in photodynamic therapy (PDT) have shown promising results in clinical applications, aided by recent improvements in light absorption efficiency and quantum yield of singlet oxygen formation. However, these photosensitizers still have several drawbacks that prevent PDT from being an efficient therapy, including lack of selectivity to diseased tissue, observation of dark toxicity, and hydrophobicity of the sensitizer. Conducting polymers are promising candidates as next generation sensitizers for PDT due to their large extinction coefficients (>107 L mol−1 cm−1), ability to undergo intersystem crossing to the triplet state at high rates, and triplet energies that are close to that of oxygen. Targeting of conducting polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene] (MEH-PPV) nanoparticles to folate receptors (FR) was achieved by development of blended nanoparticles containing amphiphilic polymer polystyrene graft ethylene oxide functionalized with carboxylic acid (PS-PEG-COOH) with chemically active moieties that can be functionalized with folic acid. The resulting organic nanoparticles are buffer stable and exhibit excellent biocompatibility in the dark. The functionalized nanoparticles (FNPs) were studied in OVCAR3 (ovarian cancer cell line, FR+), MIA PaCa2 (pancreatic cell line, FR−), and A549 (lung cancer cell line, marginally FR+). Complete selectivity of the FNPs towards FR+ cell lines was found, and is attributed to the hydrophobicity and large negative zeta potential of the nanoparticles. Quantification of PDT results by MTS assays and flow cytometry show that PDT treatment was fully selective to the FR overexpressing cell line (OVCAR3). No cell mortality was observed for the other cell lines studied here within experimental error.