There is a persistent need for
small-molecule fluorescent labels optimized for
single-molecule imaging in the cellular environment. Application of these labels comes with a set of strict requirements: strong absorption, efficient and stable emission,
water solubility and
membrane permeability, low background emission, and red-shifted absorption to avoid cell
autofluorescence. We have designed and characterized several
fluorophores, termed "DCDHF"
fluorophores, for use in live-cell imaging based on the push-pull design: an
amine donor group and a 2-dicyanomethylene-3-cyano-2,5-dihydrofuran (DCDHF) acceptor group, separated by a pi-rich conjugated network. In general, the DCDHF
fluorophores are comparatively photostable, sensitive to local environment, and their chemistries and photophysics are tunable to optimize absorption wavelength, membrane affinity, and
solubility. Especially valuable are
fluorophores with sophisticated photophysics for applications requiring additional
facets of control, such as photoactivation. For example, we have reengineered a red-emitting DCDHF
fluorophore so that it is
dark until photoactivated with a short burst of low-intensity
violet light. This molecule and its relatives provide a new class of bright photoactivatable
small-molecule fluorophores, which are needed for super-resolution imaging schemes that require active control (here turning-on) of
single-molecule emission.
