QUROPE Quantum Information Processing and Communication in Europe

Optical studies of individual molecules offer the unique possibility of investigating the local environment of single quantum objects on nanometre length scales and of employing molecular systems as non-classical light sources at room temperature. Usually, single molecule excitation is based on optical stimulation by laser radiation. In this feature article, we present an alternative approach by utilizing charge injection in combination with molecular electron–hole recombination to electrically excite single fluorescent dyes. The successful implementation of this strategy promotes the realization of electrically driven single photon sources on demand operating at room temperature and being feasible on a vast number of molecules emitting at e.g. telecommunication wavelengths. Moreover, these probes render probing the charge carrier transport and recombination on molecular length scales. In this article, we will first discuss the interaction of single charge carriers with optically excited molecules characterized by a decrease of photoluminescence intensity with increasing current density. As it is demonstrated, this effect originates from strong electrical pumping of triplet state populations upon charge carrier recombination. Secondly, the prospect of using phosphorescent emitters as electrically driven single photon sources at room temperature will be discussed. Finally, we will highlight that photoluminescence quenching of single fluorescent dyes provides a sensitive tool to quantify local current densities and recombination dynamics in operational organic light emitting diode devices with molecular spatial resolution.