From Single Chains to Aggregates, How Conjugated Polymers Behave in Dilute Solutions

Abstract

Conjugated polymers offer unique combination of easily tailored mechanical, electrical and optical properties that makes them perfect materials for the preparation of various devices such as light-emitting diodes, photovoltaic cells or field-effect transistors. However, the design and fabrication of such devices in a controlled and reproducible way are possible only if the behavior and the properties of individual polymer chains are well understood. One major problem in this respect is that aggregation often occurs even in dilute solutions and prevents the single polymer chain studies. To address this issue, in this work we employed fluorescence correlation spectroscopy (FCS) to study the behavior of a model conjugated polymer, poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) in several commonly used solvents. The very high sensitivity of FCS allowed measurements in ultradilute solutions and thus unambiguous determination of the hydrodynamic radius of single polymer chains. The solvent quality for MEH-PPV was then quantitatively evaluated from the measured logarithmic scaling of the single chain hydrodynamic radius versus the polymer molecular weight. Scaling exponents of 0.40, 0.41, and 0.43 were found in toluene, chloroform and 1,2-dichlorobenzene, respectively. These values are well below the θ-condition, emphasizing poor solvent quality for MEH-PPV, despite the fact that all studied solvents are commonly regarded as “good” solvents. In addition, by investigating the aggregation behavior of MEH-PPV at higher polymer concentrations, we found a clear relation between aggregates size and solvatochromism that indicates more extended chain conformation in larger aggregates..

Polythiophene-based conjugated polyelectrolyte: Optical properties and association behavior in solution

“…It is a sign of a tendency to aggregation/association or changes in main-chain conformations caused by the environment. At higher concentrations the aggregation tendency occurs also in the other tested solvents except methanol [39][40][41]. Description of the optical properties and behavior of solutions of conjugated polyelectrolytes is more complicated due to the presence of additional interactions in the system -coulombic forces and hydrogen bonding (see Fig.…”

5-Methyl Salicylic Acid-Induced Thermo Responsive Reversible Transition in Surface Active Ionic Liquid Assemblies: A Spectroscopic Approach

“…Therefore, slow diffusion is observed for the probe encapsulated various selfassembled systems including micelles, vesicles, proteins etc. 47,[57][58][59][60][61] Besides, the microheterogeneity in room temperature ionic liquids (RTILs) or RTILs containing assemblies have been carried out to observe molecular movement using FCS. 53,62 The basic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 14 motivation of this study is to find out how the diffusion of hydrophobic and hydrophilic molecules alter during spontaneous micelle to vesicle transition.…”

Accurate Diffusion Coefficients of Organosoluble Reference Dyes in Organic Media Measured by Dual-Focus Fluorescence Correlation Spectroscopy

“…This procedure was also used in chloroform and o-dichlorobenzene. 59, 66 Koynov et al measured the Stokes radius of commercially available, fluorescently labeled silica nanoparticles in DMSO by DLS, and used this value to calibrate their FCS setup. 49 The drawbacks of the mentioned methods are obvious.…”