Fig. 1: Imaging protonated and deprotonated phthalocyanine molecules and monitoring tautomerization processes.
a Sketch of the experiment where the fluorescence energy (hν) of a phthalocyanine molecule is progressively Stark-shifted (δhνi) by charges located at the center of the chromophore. b, d, f STM images (2.7 × 2.7 nm2) of a phthalocyanine molecule on 3ML-NaCl/Ag(111). The images of the HOMO were all recorded at I = 10 pA, with voltage V = −2.5 V for H2Pc, V = −1.5 V for HPc− and V = −2 V for Pc2−. The LUMO were recorded at I = 10 pA, V = 0.5 V for (b) H2Pc, I = 2.3 pA, V = 1.43 V for (d) HPc− and I = 10 pA, V = 1.65 V for (f) Pc2−. The LUMO images of H2Pc and HPc− reveal two and four different patterns, respectively, in successive images. The dots in the LUMO images of HPc− indicate the side where the remaining hydrogen atom is located. c, e, g Relative tip-sample distance (Δz) time traces and their histograms recorded at a bias voltage of −2.5 V on (c) H2Pc, (e) HPc−, and (g) Pc2− , and at constant current (Iset−point = 10 pA for H2Pc and 5 pA for HPc− and Pc2−).
