Solvent-induced photoemissions of high-energy chromophores of conjugated Polymer MEH-PPV: Role of conformational disorder

Abstract

This study examined the photoemission behaviors of isolated chains of poly[2-methoxy, 5-(2'-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV) dispersed in various solvents including dichloromethane, chloroform and tetrahydrofuran(THF). A change in polymer-solvent interactions in these solutions caused the MEH-PPV chains to adopt different local conformations, which in turn affected their radiative de-excitation pathways. For the polymer in dichloromethane and chloroform, in which the conjugated chains are relatively extended, photoemission occurs mostly at the long chromophores with lowest HOMO-LUMO energy gap. Their emission spectra showed a main peak at ~560 nm. Dual photoemission of high-and low-energy chromophores was observed when the conjugated chains were forced to partially collapse in a poor solvent THF. Novel high-energy peaks and a typical low-energy peak were detected at ~414 nm and ~554 nm, respectively. The observation of the high-energy peaks indicates significant suppression of the intrachain energy transfer process, which was attributed to the increase in conformational disorder in the partially collapsed coils. An analysis of the excitation spectra suggests that the high-energy peaks belong to short chromophores constituting of one or two repeat units. This study systematically investigated the effects of polymer concentration, temperature and single bond defects along the backbone on the photoemission of the high-energy chromophores.

Electronic and Vibrational Coherences in Resonance Energy Transfer along MEH-PPV Chains at Room Temperature

“…The NPs dispersed in water manifest broadened absorption and red-shifted fluorescence spectra compared to those of the polymer in CF solution. The blue-shifted contribution to the absorption band is consistent with a small overall decrease in the conjugation length, attributable to the bending or kinking of the polymer backbone. , A red tail is also evident in the absorption spectrum of NPs, indicating the presence of aggregate states formed by interactions between segments of the polymer chain. , On the other hand, in good solvents like CF, the individual polymer chains are expected to assume a relatively open and straight conformation, which maximizes favorable solute−solvent interactions, , as recently shown by theoretical studies …”

Ultralow Dielectric Constant Polyarylene Ether Nitrile/Polyhedral Oligomeric Silsesquioxanes Foams with High Thermal Stabilities and Excellent Mechanical Properties Prepared by Supercritical CO2

“…Therefore, with the increase of frequency, the ε gradually decreases, and the dielectric loss is consistent with the change of ε . [ 49–51 ] The ε and tan δ of the PEN/POSS composites material increases initially and decreases afterward with the increase of the POSS content. Compared with pure PEN matrix, the dielectric constant of PEN/POSS‐3 increased from 3.43 to 3.48 at 1 kHz, and the dielectric loss raised from 0.0348 to 0.0368.…”

Effects of steric anthracene moieties and keto defects on photophysics and color stability of poly(9,9-di(2-ethylhexyl)fluorene-stat-anthracene) in different local environments

“…Chemists generally take the approach of structural modification [7][8][9][10][11][12][13][14] while physicists can achieve the desired properties via the control of chain conformation and molecular packing. [15][16][17][18][19] Polyfluorene is one type of conjugated polymer that exhibits a blue-color emitting with high quantum efficiency. 7,10 The photophysical properties of this class of polymer have been known to depend on various molecular parameters.…”