Experimental and Theoretical Investigations of Environmentally Sensitive Single-Molecule Fluorophores†

The development of new fluorescent dyes for use in single-molecule imaging is an important challenge due
to the numerous problems in biomolecular and materials science that can benefit from measurements at the
level of individual molecules. A new class of fluorophores has been described recently that is not only well
suited for single-molecule imaging but also shows strong sensitivity to the local environment. These molecules,
known as the DCDHFs, contain an amine donor and a dicyanodihydrofuran acceptor linked by a conjugated
unit (benzene, thiophene, styrene). The environmental sensitivity of these dyes can be characterized through
bulk spectroscopic and fluorescence measurements as a function of solvent and solvent viscosity. Excited
state lifetime data for single DCDHF molecules in polymers also demonstrate the value of the DCDHFs as
probes of their local environment. To further understand the behavior, a series of electronic structure calculations
have been completed, which yield insight into how certain twists within the DCDHF molecule may affect
radiative and nonradiative processes. These insights will help direct synthetic modifications in the molecular
structure to improve the environmental sensitivity and fluorescence quantum yield of these single-molecule
probes.