Separating Nonsense in Decay and Splicing

Single-molecule studies often require that molecules be well-spaced so that their individual spectral features can be discriminated. Hettich et al. (p. 385; see the cover and the Perspective by Orrit) show that by using a nearby scanning probe tip to supply a local electric field and induce Stark shifts, molecules of terrylene, embedded in a p-terphenyl crystal, that are only 12 nanometers apart can be resolved for samples at cryogenic temperatures. The authors then looked at the effects of dipole-dipole coupling between these molecules in the absence of the field. A new line appears nearly midway between the optical lines of the coupled system that arises through the two-photon excitation of pair’s doubly excited state. When the pair is excited through a new central line, the emitted photons exhibit “bunching”—they are emitted in pairs. These results suggest that this entanglement of molecular emission could be further manipulated with larger applied electric fields.