Reversible Assembly of Terpyridine Incorporated Norbornene-Based Polymer via a Ring-Opening Metathesis Polymerization and Its Self-Healing Property

We induced a terpyridine moiety into a norbornene-based polymer to demonstrate its self-healing property, without an external stimulus, such as light, heat, or healing agent, using metal–ligand interactions. We synthesized terpyridine incorporated norbornene-based polymers using a ring-opening metathesis polymerization. The sol state of diluted polymer solutions was converted into supramolecular assembled gels, through the addition of transition metal ions (Ni2+, Co2+, Fe2+, and Zn2+). In particular, a supramolecular complex gel with Zn2+, which is a metal with a lower binding affinity, demonstrated fast self-healing properties, without any additional external stimuli, and its mechanical properties were completely recovered

Aggregates of conjugated polymers: bottom-up control of mesoscopic morphology and photophysics

Abstract Conjugated polymer (CP) aggregates have been the focus of considerable research, as these mesoscopic entities, compared with single CP chains, provide environments more analogous to those present in polymer-based optoelectronics in terms of the complexity of morphology and chain interactions; thereby, such aggregates hold the potential to provide insights into structure–function relationships highly relevant to optoelectronic device efficiency and stability. This review article highlights single-aggregate spectroscopy studies of CP aggregates based on a combination of solvent vapor annealing and single-molecule fluorescence techniques and draws mesoscopic connections between morphology, electronic coupling, and photophysics in CPs. This molecular-level understanding will pave the way for the bottom-up control of optoelectronic properties from the molecular to the device-length scale

Localizing Exciton Recombination Sites in Conformationally Distinct Single Conjugated Polymers by Super-resolution Fluorescence Imaging

To thoroughly elucidate how molecular conformation and photophysical properties of conjugated polymers (CPs) are related requires simultaneous probing of both. Previous efforts used fluorescence imaging with one nanometer accuracy (FIONA) to image CPs, which allowed simultaneous estimation of molecular conformation and probing of fluorescence intensity decay. We show that calculating the molecular radius of gyration for putative folded and unfolded poly(2-methoxy-5-(2′-ethylhexyloxy)1,4-phenylenevinylene) (MEH-PPV) molecules using FIONA underestimates molecular extension by averaging over emitters during localization. In contrast, employing algorithms based on single molecule high resolution imaging with photobleaching (SHRImP), including an approach we term all-frames SHRImP, allows localization of individual emitters. SHRImP processing corroborates that compact MEH-PPV molecules have distinct photophysical properties from extended ones. Estimated radii of gyration for isolated 168 kDa MEH-PPV molecules immobilized in polystyrene and exhibiting either stepwise or continuous intensity decays are found to be 12.6 and 25.3 nm, respectively, while the distance between exciton recombination sites is estimated to be ∼10 nm independent of molecular conformation

Conformation-Dependent Photostability among and within Single Conjugated Polymers

The relationship between photostability and conformation of 2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) conjugated polymers was studied via excitation polarization modulation depth (<i>M</i>) measurements. Upon partial photobleaching, <i>M</i> distributions of collapsed, highly ordered MEH-PPV molecules shifted toward lower values. Conversely, <i>M</i> distributions of MEH-PPV molecules with random coil conformations moved toward higher values after partial photobleaching. Monte Carlo simulations of randomly distributed dipole moments along polymer chains subjected to partial photobleaching revealed that a statistical effect leads to an increase in peak <i>M</i> value. Decreases in <i>M</i> values seen experimentally in the population of MEH-PPV molecules with high <i>M</i> values, however, are due to conformation-dependent photostability within single MEH-PPV polymers. We show that, while folded MEH-PPV molecules are relatively more photostable than extended MEH-PPV molecules in an ensemble, extended portions of particular molecules are more photostable than folded domains within single MEH-PPV molecules

Segmental Dynamics of an Isolated Component Polymer Chain in Polymer Blends Near the Glass Transition

The segmental dynamics of a component chain isolated in its blending partner chains is examined using the reorientation of polymer-tethered fluorescent probes near the glass transition. It is found that the temperature dependence of the dynamics of an isolated component follows that of the other component, with a horizontal shift corresponding to the glass transition temperature modification, which may result from a local composition of ≈10% isolated component. On the contrary, the dynamic heterogeneity, another key dynamic feature near the glass transition, shows that the local dynamic environment of an isolated component becomes either as heterogeneous as a more inherently heterogeneous component or more heterogeneous than either. These observations emphasize that not only the chain connectivity but also the dynamic modulation of a component by the other component needs to be addressed in order to understand the segmental dynamics of an isolated component in polymer blends

Extraction of Rotational Correlation Times from Noisy Single Molecule Fluorescence Trajectories

Monitoring single molecule probe rotations is an increasingly common approach to studying dynamics of complex systems, including supercooled liquids. Even with advances in fluorophore design and detector sensitivity, such measurements typically exhibit low signal to noise and signal to background ratios. Here, we simulated and analyzed orthogonally decomposed fluorescence signals of single molecules undergoing rotational diffusion in a manner that mimics experimentally collected data of probes in small molecule supercooled liquids. The effects of noise, background, and trajectory length were explicitly considered, as were the effects of data processing approaches that may limit the impact of noise and background on assessment of environmental dynamics. In many cases, data treatment that attempts to remove noise and background were found to be deleterious. However, for short trajectories below a critical signal to background threshold, a thresholding approach that successfully removed data points associated with noise and spared those associated with signal allowed for assessment of environmental dynamics that was as accurate and precise as would be achieved in the absence of noise

Fast Crystal Growth from Organic Glasses: Comparison of <i>o</i>‑Terphenyl with its Structural Analogs

Crystal growth kinetics and liquid dynamics of 1,2-diphenylcyclopentene (DPCP) and 1,2-diphenylcyclohexene (DPCH) were characterized by optical microscopy and dielectric spectroscopy. These two molecules are structurally homologous and dynamically similar to the well-studied glassformer <i>ortho</i>-terphenyl (OTP). In the supercooled liquid states of DPCP and DPCH, the kinetic component of crystal growth <i>u</i>_kin has a power law relationship with the primary structural relaxation time τ_α, <i>u</i>_kin ∝ τ_α^–ξ (ξ ≈ 0.7), similar to OTP and other fragile liquids. Near the glass transition temperature (<i>T</i>_g), both DPCP and DPCH develop much faster crystal growth via the so-called GC (glass to crystal) mode, again similar to the behavior of OTP. We find that the α-relaxation process apparently controls the onset of GC growth, with GC growth possible only at sufficiently low fluidity. These results support the view that GC crystal growth can only occur in systems where the liquid and crystal exhibit similar local packing arrangements