Evidence for electric field-assisted dissociation of the excited singlet state into charge carriers in MEH–PPV

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

“…Application of the electric field dissociates excitons into electron-hole pairs that become charge carriers. 11 The field-induced quenching of PL increases with increasing wavenumber of excitation light, indicating that the efficiency of the field-assisted dissociation increases with increasing excitation energy. These results clearly show that the field-induced generation of electron-hole pairs through excitons of the conjugated polymer occurs from nonrelaxed higher vibrational levels of the excited state in competition with relaxation to the emitting state.…”

“…As a result, the intersystem crossing may be decelerated by the applied electric field, resulting in the increase of the fluorescence intensity. In contrast with the enhancement, electric-field-induced quenching of PL was reported in conjugated polymers, such as in poly(p-terphenylene vinylene), 24 MEH-PPV, 11 poly(p-phenylphenylenevinylene) blended with polycarbonate, [25][26][27] or poly(p-phenylenevinylene). 28 As the origin of the field-induced quenching of PL reported so far, an exciton model and a band model have been proposed.…”

“…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.…”

“…7 For MEH-PPV, application of an electric field decreases the fluorescence lifetime, indicating that the dominant mode of fluorescence quenching is lifetime quenching. 11 In contrast, the electric field effect on the lifetime of PL of S3-PPV is very small, but the quenching of PL occurs with excitation into higher excited states, suggesting that only the nonradiative process at the photoexcited state that competes with relaxation to the emitting state is well affected by electric fields. The nonradiative process of S3-PPV under consideration is assigned to a fieldassisted generation of electron-hole pairs, as described above.…”

Dynamical simulation of exciton dissociation in poly(para-phenylenevinylene) systems

“…the binding energy of the exciton. In particular, it has been shown that the field-induced dissociation is ultrafast and leads to the creation of a pair of oppositely charged polarons on separate chains [7][8][9][10]. The initial phase of charge transport following electron-hole separation is also included in our simulations.…”