<p></p><p>Voltage imaging with
fluorescent indicators offers a powerful complement to traditional electrode or
Ca<sup>2+</sup>-imaging approaches for monitoring electrical activity. Small
molecule fluorescent indicators present the unique opportunity for exquisite
control over molecular structure, enabling detailed investigations of
structure/function relationships. In this paper, we tune the conjugation
between aniline donors and aromatic π
systems within the context of photoinduced electron transfer (PeT) based
voltage indicators. We describe the design and synthesis of four new
voltage-sensitive fluorophores (VoltageFluors, or VFs). Three of these dyes
have higher relative voltage sensitivities than the previously-reported
indicator, VF2.1.Cl. We pair these new indicators with existing VFs to
construct a library of voltage indicators with varying degrees of conjugation
between the aniline nitrogen lone pair and the aromatic π system. Using a combination of steady-state and
time-resolved fluorescence spectroscopy, cellular electrophysiology, fluorescence
lifetime imaging microscopy (FLIM), and functional imaging in mammalian neurons
and human cardiomyocytes, we
establish a detailed link between the photophysical properties of VF dyes and
their ability to report on membrane potential dynamics with high signal-to-noise.
Anilines with intermediate degrees of conjugation to the aromatic π system experience intermediate rates
of PeT and possess the highest absolute voltage sensitivities. Measured using FLIM in
patch-clamped HEK cells, we find that the absolute voltage sensitivity of
fluorescence lifetime (∆τ<sub>fl</sub> per mV) provides the best predictor of
dye performance in cellular systems.</p><br><p></p>
Fluorescence lifetime predicts performance of voltage sensitive fluorophores in cardiomyocytes and neurons