Singlet Energy Transfer as the Main Pathway in the Sensitization of Near‐Infrared Nd 3+ Luminescence by Dansyl and Lissamine Dyes

In general, sensitization of lanthanide( III ) ions by organic sensitizers is regarded to take place via the triplet state of the sensitizers. Herein, we show that in dansyl‐ and lissamine‐functionalized Nd 3+ complexes energy transfer occurs from the singlet state of the sensitizers to the Nd 3+ center. No sensitized emission was observed in the corresponding complexes with Er 3+ , Yb 3+ , and Gd 3+ ions. Furthermore, the fluorescence of the sensitizers was quenched only in the Nd 3+ complex and not in the complexes with the other ions. Only Nd 3+ centers can accept energy from the singlet state of the dyes, because the excited states of Nd 3+ have a high spectral overlap with the fluorescence of the dansyl and lissamine sensitizers, and because the selection rules allow a fast energy transfer, which apparently is competitive with the fluorescence.