Equilibrium Flexibility of a Rigid Linear Conjugated Polymer

Abstract

The unusual electronic and optical properties of many electroluminescent and conducting polymers arise from extended conjugation along the polymer backbone, which can also lead to insolubility, aggregation, and gelation. Synthetic efforts to produce an optimal structure require a balance between the persistence length and the effective conjugation length for the successful implementation of these materials in photonic and electronic devices. In this study, we have investigated the solution properties of a group of poly(phenyleneethynylenes) using a variety of light scattering techniques, including polarized and depolarized intensity measurements, dynamic light scattering, and size exclusion chromatography with a multiangle light scattering detector (SEC/LS). Interpretation of light scattering in the presence of absorption, fluorescence, and optical anisotropy is discussed. The molecular weights determined by light scattering encompassed the range from 10 × 105 to 5 × 106, with the root-mean-square radius of gyration as high as 250 nm. The results may be interpreted with a wormlike chain model to yield a persistence length of about 15 nm, so that these high-M polymers are coil-like in solution, rather than “rigid rods”. This persistence length is still expected to be several times larger than the effective conjugation length.

Energy Transport along Conjugated Polymer Chains with Extended Radiative Lifetimes: A Theoretical Study

“…This is quantified by the calculated end-to-end distances of hR ee = 92 nm in PPE and hR ee i = 42 nm in PTPE, after averaging over 1000 realizations of a 100-unit-long polymer chain. Our simulations for PPE qualitatively reproduce the trends observed experimentally by Swager et al that low molecular weight fractions of this polymer show rigid-rod behavior [50] . On the other hand, PTPE chains show a higher propensity to behave as "wormlike" chains.…”

Fluorous Biphase Synthesis of a Poly(p‐phenyleneethynylene) and its Fluorescent Aqueous Fluorous‐Phase Emulsion

“…Dynamic light scattering (DLS) analysis showed that the average length of P1 is 16 nm, a value that corresponds to the typical persistence length of long PPEs. [8] DLS measurements in perfluorodecalin also showed similar length distributions. When P1 was end-capped with 1-bromo-4-tertbutylbenzene, no signals corresponding to the tert-butyl group were observed in the 1 H NMR spectrum, indicating a high degree of polymerization (> 20).…”

Chain geometry, solution aggregation and enhanced dichroism in the liquidcrystalline conjugated polymer poly(9,9-dioctylfluorene)

“…We have undertaken an experimental determination of C v , closely following the procedure outlined by Cotts et al in [6]. The approach is to use coupled gel permeation chromatography/light scattering [GPC/LS] measurements.…”