Disorder in P3HT Nanoparticles Probed by Optical Spectroscopy on P3HT-b-PEG Micelles.

We employ photoluminescence (PL) spectroscopy on individual nanoscale aggregates of the conjugated polymer poly(3-hexylthiophene), P3HT, at room temperature (RT) and at low temperature (LT) (1.5 K), to unravel different levels of structural and electronic disorder within P3HT nanoparticles. The aggregates are prepared by self-assembly of the block copolymer P3HT-block-poly(ethylene glycol) (P3HT-b-PEG) into micelles, with the P3HT aggregates constituting the micelles' core. Irrespective of temperature, we find from the intensity ratio between the 0-1 and 0-0 peaks in the PL spectra that the P3HT aggregates are of H-type nature, as expected from π-stacked conjugated thiophene backbones. Moreover, the distributions of the PL peak ratios demonstrate a large variation of disorder between micelles (inter-aggregate disorder) and within individual aggregates (intra-aggregate disorder). Upon cooling from RT to LT, the PL spectra red-shift by 550 cm-1, and the energy of the (effective) carbon-bond stretch mode is reduced by 100 cm-1. These spectral changes indicate that the P3HT backbone in the P3HT-b-PEG copolymer does not fully planarize before aggregation at RT and that upon cooling, partial planarization occurs. This intra-chain torsional disorder is ultimately responsible for the intra- and inter-aggregate disorder. These findings are supported by temperature-dependent absorption spectra on thin P3HT films. The interplay between intra-chain, intra-aggregate, and inter-aggregate disorder is key for the bulk photophysical properties of nanoparticles based on conjugated polymers, for example, in hierarchical (super-) structures. Ultimately, these properties determine the usefulness of such structures in hybrid organic-inorganic materials, for example, in (bio-)sensing and optoelectronics applications.

Synthesis, Surface Grafting, and Fabrication of Ultrathin Polymeric SAMFETs with High Field-Effect Mobility.

Densely surface-grafted monolayer (3-4 nm) poly(3-hexylthiophene) (P3HT) brushes are prepared by click chemistry. For this, P3HT chains with alkyne end groups were synthesized and chemically coupled to a surface-immobilized self-assembled monolayer (SAM) having azide functionality in an organic field-effect transistor channel. The grafted P3HT-alkyne with a molecular weight of Mn,MALDI = 11 400 g mol-1 ( Mn,SEC = 17 400 g mol-1) and a narrow distribution of D = 1.15, has the highest reported molecular weight for surface-immobilized P3HT brushes. We show the successful grafting of P3HT on the substrate surface with atomic force microscopy, contact angle, and absorption studies. From the film thickness, we can calculate the reduced tethered densities of ∑ = 10.3-12.1, which is indicative of the monolayers being in the true brush regime with high grafting density that is enough to form a compact self-assembled monolayer. The aggregation behavior of the films is characterized by UV-vis spectroscopy and compared to linear P3HT and a bottlebrush copolymer polystyrene- g-P3HT (PS- g-P3HT) with similar P3HT lengths. For such an SAM-based organic field-effect transistor (SAMFET) nanodevice with an ultrathin P3HT layer of 3-4 nm, a very high field-effect mobility of up to 1.8 × 10-3 cm2 V-1 s-1 is achieved in channel lengths of 5-20 µm, which is nearly 2 orders of magnitude higher than reported values for polymer-based SAMFETs.

Measuring Cumulative Exposure to Oxygen with a Diphenylphosphine-Alkyl Naphthaleneimide Luminescence Turn-On Dyad.

2-(2-Diphenylphosphanylethyl)benzo[de]isoquinoline-1,3-dione is a poorly luminescent, photoinduced-electron-transfer (PET) dyad, NI-(Ph)2 P:, in which the luminescence of its naphthaleneimide (NI) part is quenched by the lone-pair electrons of the phosphorus atom of the (Ph)2 P: group. Photoinduced oxidation of (Ph)2 P: to (Ph)2 P=O by molecular oxygen regenerates the luminescence of the NI group, because the oxidized form (Ph)2 P=O does not serve as a quencher to the NI system. The oxidation of (Ph)2 P: is thermally inaccessible. The NI-(Ph)2 P: system was applied to monitoring the cumulative exposure of oxidation-sensitive goods to molecular oxygen. The major advantage of this new PET system is that it reacts with oxygen only via the photoinduced channel, which offers the flexibility of monitoring the cumulative exposure to oxygen in different time periods, simply by varying the sampling frequency. Electronic-energy calculations and optical spectroscopic data revealed that the luminescence turn-on upon reaction with molecular oxygen relies on a PET mechanism.

Superparamagnetic and fluorescent thermo-responsive core-shell-corona hybrid nanogels with a protective silica shell.

We present the preparation and the characterization of the solution behavior and functional properties of superparamagnetic and/or fluorescent, thermo-responsive inorganic/organic hybrid particles with an intermediate protective silica shell and a smart polymer corona. These well-defined multifunctional nanogels were prepared via two consecutive encapsulation processes of superparamagnetic Fe(2)O(3) nanoparticles (NPs) and/or fluorescent CdSe(ZnS) semiconductor nanocrystals with a silica layer and a crosslinked poly(N-isopropylacrylamide) (PNIPAAm) polymer shell. First, the different NPs were entrapped into a silica shell using a microemulsion process. Therein, the precise adjustment of the conditions allows to entrap either several particles or single ones and to tailor the thickness of the silica shell in the range of 20-60 nm. In a second step, a polymer coating, i.e. thermosensitive PNIPAAm, was attached onto the surface of the multifunctional core-shell particles via free radical precipitation polymerization, furnishing multifunctional core-shell-corona hybrid nanogels. Analyses of the functional properties, i.e. optical brightness and magnetic moments, along with transmission electron microscopy reveal near monodisperse hybrid nanoparticles that retain the intrinsic properties of the original nanocrystals. Additionally, we demonstrate the drastically increased chemical stability due to the barrier properties of the intermediate silica layer that protects and shields the inner functional nanocrystals and the responsive character of the smart PNIPAAm shell.