Fluorescent probes that are able to directly measure viscosity are attractive candidates for the study of intracellular environments. We report a new class of luminescent rotors, based on the sensitized emission of a terbium(III) complex. A 4-fold increase in both quantum yield and luminescence lifetime was observed in viscous media for the studied complexes, with a lifetime ranging from 0.23 to 0.89 ms over a broad range of viscosities (0.6-1200 cP). The presented approach, relying on the millisecond-scale luminescence lifetime of the lanthanide ions, was applied to fixed T24 cancer cells using temporal sampling lifetime imaging microscopy.

A new visible-light photoactivation mechanism based on sensitized triplet fusion between two excited ZnTPP chromophores achieves free-radical polymerization from acrylate monomers without additives. The combined results demonstrate that the upper S 2 excited state of ZnTPP is oxidatively quenched by the acrylates, resulting in the formation of an acrylate radical anion that engages in radical chain polymerization. Well-defined macro-and microscopic polymer gels were readily produced in a facile manner using green and yellow visible photons.