  We propose using halogenated organic dyes as nanoprobes for electric field
and show their greatly enhanced Stark coefficients using density functional
theory (DFT) calculations. We analyse halogenated variants of three molecules
that have been of interest for cryogenic single molecule spectroscopy,
perylene, terrylene, and dibenzoterrylene, with the zero-phonon optical
transitions at blue, red, and near infrared. Out of all the combinations of
halides and binding sites that are calculated, we have found that fluorination
of the optimum binding site induces a dipole difference between ground and
excited states larger than 0.5 D for all three molecules with the highest value
of 0.69 D for fluoroperylene. We also report on synthesis of 3-fluoroterrylene
and bulk spectroscopy of this compound in liquid and solid organic
environments.
