  Organic molecules with nonlinear optical behavior have advanced a wide range
of fields spanning from integrated photonics to biological imaging. With
advances in microscopy, an emerging application is multifunctional nonlinear
organic imaging agents. Unlike conventional imaging probes which simply emit
light through single or multi photon processes, multifunctional materials allow
systems to be simultaneously imaged and controlled. In this work, we report a
multifunctional molecular probe for modulating and reporting electric fields.
The probe molecule consists of two distinct functional modules which are
connected by a long alkyl chain. The electric field detector module relies on
the two-photon (2p) imaging agent and photo-induced electron transfer (PeT)
dye, TPE. Two-photon imaging agents have demonstrated less damage and larger
penetration depths in cells and live tissue imaging. The electric field
modulator module relies on the organic photoconductor, NAI. To reduce
cross-talk and optimize absorption and emission wavelengths, the molecular
structure is first studied using density functional theory modeling, and then
the multi-functional molecular probe is synthesized. The photophysical,
photoconductivity, and biotoxicity of the probe molecule are studied in a range
of solvents and solid state, and the results agree with the theoretical
predictions. Specifically, 2p excitation in a biocompatible solvent is
demonstrated, the photoconductivity is rapid and reversible, and the material
has low cytotoxicity. Additionally, the entire system is optically controlled,
including signal read-out, and the two modules can be operated simultaneously
or individually. This work sets the stage for modulation and detection of
bioelectric fields in a range of cell and tissue types.
