Electric Field Effects on Internal Conversion:  An Alternative Mechanism for Field-Induced Fluorescence Quenching of MEH-PPV and Its Oligomers in the Low Concentration Limit

Abstract

In a previously published study (J. Phys. Chem. B 2006, 110, 7732−7742), we reported field-induced fluorescence quenching in both poly[2-methoxy,5-(2‘-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and several model oligomers in solvent glass matrices at high dilution (<0.1% by weight). The observed quenching is not readily explained by field-induced exciton dissociation or by the presence of free charges, two mechanisms that have been invoked to explain this phenomenon by previous authors. A model is developed here that ascribes the observed fluorescence quench in dilute samples to an energetic shift of the relaxed excited state caused by the electric field resulting in increased nonradiative relaxation. To determine whether the relevant nonradiative pathway is intersystem crossing or internal conversion, analytical expressions are derived for each of these two mechanisms. Only the expression derived for the Stark effect on the rate of internal conversion quantitatively predicts the magnitude of quench observed in MEH-PPV and in the oligomeric species.

Electric-Field-Induced Enhancement/Quenching of Photoluminescence of π-Conjugated Polymer S3-PPV: Excitation Energy Dependence

“…12 In contrast with ∆µ, the present value of ∆R is 0.01-0.1 times those obtained for the transition between S 0 and the 1 B u state of MEH-PPV or OPPVs in a glassy solvent, 12,13 indicating that the excited state of S3-PPV that shows strong absorption with a maximum ∼22 500 cm -1 differs somewhat from those of MEH-PPV or OPPVs in a glassy solvent. It is worth mentioning that ∆R of a polymer film of PPV, ∼3300 Å 3 /f 2 , is 10-100 times as large as the present value, whereas the magnitude of ∆R of a polymer film of MEH-PPV, ∼116 Å 3 /f 2 , is similar to the present value of S3-PPV.…”

“…This value of ∆R j is similar to that derived for PPV. 13 As shown in Table 1, the value of ∆R j evaluated from the E-PL spectra of OPPV in a dilute solvent glass ranged from 500 to 3000 Å 3 /f 2 . The value of ∆R j obtained from E-PL of MEH-PPV or OPPVs in a glassy solvent is similar to that obtained from E-A, indicating no difference of electronic properties between the absorbing and emitting states.…”

“…8,9 The absorption and fluorescence of PPV and its soluble derivatives MEH-PPV, poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene, were investigated in the presence of an electric field; values of the binding energy and the variation of the dipole moment and polarizability between the emitting and the ground states were estimated. [10][11][12][13] One PPV derivative, S3-PPV, having sulfide long chains is soluble in common organic solvents; the chemical structure is shown in Chart 1. Using S3-PPV in double-layer light-emitting devices, a maximum luminescence of 6073 cd m -2 with a current yield of 0.82 cd A -1 was obtained.…”

Single particle spectroscopy on composite MEH-PPV/PCBM nanoparticles

“…These sites are coupled to each other by a fast energy transfer process, showing that even single polymer chains exhibit bulk-like behavior to a certain extent and thus are good simplified model systems to study photophysical processes in conducting polymer bulk materials. More recently, reversible photooxidation and deep charge trapping were investigated for single conducting polymer chains in a functioning device, and Stark shifts of conducting polymer spectra by electrical fields were reported [16,[28][29][30].…”

Stark shifts and exciton dissociation in CdSe nanoparticle grafted conjugated polymer

“…So far, the modified known PPV derivatives are poly[2-methoxy,5-(2 0ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV), oligophenylenevinylenes (OPPVs), poly[2-(phenyl)-3-(4 0 -(3, 7-dimethyloctyloxy)phenyl)-1,4-phenylenevinylene-co-2-(11 0decyl sulfanylundecanyloxy)-5-methoxy-1,4-phenylene vinylene] (S3PPV), etc. [4][5][6][7][8][9] In a previous report, we proposed a sulfide-substituted PPV derivative S3PPV, which is soluble in common organic solvents and examined UV-visible optical properties in the absence and presence of external electric field. 9 Here, we present a further modified derivative, a CdSe nanoparticles implanted S3PPV, i.e., CdSe-S3PPV.…”