Long-range energy transfer of singlet and triplet excitations in dye-dopedtris(phenylquinoxaline)

In order to obtain efficient organic light-emitting diodes (OLED) it is nec essary to funnel both singlet and triplet excitons generated by electroexci tation to the emitting dye molecule. Energy transfer plays thereby a decisi ve role. We have studied mechanisms and kinetics of the energy transfer pro cess involving singlet and triplet excitations in a donor-acceptor system s uitable for use as active layer in OLEDs. Fluorescent and phosphorescent tr is(phenylquinoxaline) served as donor and a red emitting platinum porphyrin as acceptor molecule. The results of our investigations show that efficien t energy transfer from the singlet and triplet excited state of the donor t o the acceptor molecules takes place by combined long-range dipole-dipole i nteraction and diffusion. Due to the very different oscillator strengths of radiative transitions from the singlet and triplet excited state to the si nglet ground state the rate of energy transfer of triplet excitons is sever al orders of magnitude slower than that of singlet excitons. Since, however , the lifetime of both states differ by the same order of magnitude the tra nsfer efficiency is comparable. (C) 2001 American Institute of Physics.