PHOTOEXCITATION SPECTROSCOPY OF CONDUCTING-POLYMER-C(60) COMPOSITES -PHOTOINDUCED ELECTRON-TRANSFER

We present a comparative study of the steady-state photoinduced absorp tion and photoinduced electron-spin-resonance (ESR) spectra of conduct ing polymers mixed with the fullerene C60. For conjugated polymers wit h nondegenerate ground states as donors, electron transfer takes place prior to either radiative or nonradiative recombination of pi-electro n photoexcitations on the conducting polymer. In the case of a conjuga ted polymer with a degenerate ground state as donor, the structural re laxation associated with the formation of charged solitons is faster; and no indications of photoinduced charge transfer are observed. Thus, composites using a derivative of poly(1,6-heptadyene) as donor do not exhibit long-lived charge separation, whereas charge transfer and cha rge separation are observed in composites using poly(p-phenylene vinyl ene) or polythiophene derivatives as donors. The relaxation (as a func tion of temperature) of the charge separated state is studied through photoinduced absorption spectroscopy (excitation spectroscopy) and pho toinduced ESR. The results are discussed in terms of designing suitabl e donor-acceptor pairs for photoinduced electron transfer using conduc ting polYMers and C60 as donor and acceptor, respectively.