Fig. 2: Response of fluorescent probe to electrodynamic and electrostatic environment.

a STML spectra of a PTCDA tip in front of Ag(111) (red) and of 2 ML NaCl (blue), and of the flat-lying PTCDA on 3 ML NaCl excited with a metal tip (black). This data set was recorded with the same molecule. The plasmonic response of the tip (without molecule attached) is presented in Supplementary Fig. 1 showing a very broad emission around 1.4–1.5 eV. b X⁻ emission spectra (yellow, orange and red) for three different PTCDA tips above Ag(111) and the associated plasmonic spectra (in gray) recorded prior to the molecular functionalization of the tip. The FWHM of the X⁻ peak increases for resonant plasmon-trion conditions. c FWHM of X⁻ as a function of the energy of the plasmon peak maximum. These data were recorded at an identical set point (I = 30 pA, V = 2.5 V) and stem from 13 macro- or microscopically different tips. d X⁻ emission spectra for varying PTCDA-tip-to-surface separation (left, V = 2.5 V) and for varying bias voltage (right, z = 2.2 nm). A red shift of the central emission is observed upon reducing z or increasing V. e Relative shift of the central emission line μ extracted from the data in (d), taking the reference energy μ₀ from the bottom spectrum in (d). Color coding corresponds to the spectra in (d). Spectra in (a, b, d) are offset vertically for easier comparison. Both μ and the FWHM of the spectra were extracted by fitting a Lorentzian function to the data, accounting for the vibronic satellites with Lorentzian functions when necessary. Acquisition parameters in (a) from top to bottom: V = 2.5, 2.5, −2.5 V, I = 60, 50, 60 pA, \(t=6,\,6,\,30\,\min\). Spectra acquisition parameters for (b–d) are detailed in Supplementary Note 1.4. Source data are provided as a Source Data file.