For many years, numerous fluorescent
probes have been synthesized
and applied to visualize molecules and cells. The development of such
probes has accelerated biological and medical investigations. As our
interests have been focused on more complicated systems in recent
years, the search for probes with sensitive environment off–on
response becomes increasingly important. For the design of such sophisticated
probes, theoretical analyses of the electronically excited state are
inevitable. Especially, understanding of the nonradiative decay process
is highly desirable, although this is a challenging task. In this
study, we propose an approach to treat the solvent fluctuation based
on the reference interaction site model. It was applied to selected
bioimaging probes to understand the importance of solvent fluctuation
for their off–on response. We revealed that the this switching
process involves the nonradiative decay through the charge transfer
state, where the solvent relaxation supported the transition between
excited and charge transfer states. In addition, energetically favorable
solvent relaxation paths were found due to the consideration of multiple
solvent configurations. Our approach makes it possible to understand
the nonradiative decay facilitated by a detailed analysis and enables
the design of novel fluorescent switching probes considering the effect
of solvent fluctuation
