Supporting information for: Breaking Degeneracy of Tautomerization. Metastability from Days to Seconds

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1 Supporting information for: Breaking Degeneracy of Tautomerization Metastability from Days to Seconds Jens Kügel,, Aimee Sixta,, Markus Böhme, Andreas Krönlein, and Matthias Bode, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany, University of Texas at Austin, Austin 78712, USA, and Wilhelm Conrad Röntgen-Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D Würzburg, Germany Scanning tunneling spectroscopy and di /du -mapping Fig. S1(a) shows a point spectroscopy curve taken at one of the eight lobes of the HOMO [cf. Fig. S1(b) and (c)]. There are three main features visible in the spectroscopy curve, which is the HOMO located at an energy of U 1.3 ev, the LUMO centered at an energy of U 0.7 ev and the surface state of the Ag(111) substrate located close to the Fermi energy. Topographic images and di /du -maps were taken at the bias voltage of the HOMO [cf. Fig. S1(b) and (c)] and of the LUMO [cf. Fig. S1(d) and (e)]. Whereas the HOMO is To whom correspondence should be addressed Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany University of Texas at Austin, Austin 78712, USA Wilhelm Conrad Röntgen-Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D Würzburg, Germany S1

2 d I/d U (na/v) LUMO HOMO (a) 3 (b) (d) (c) (e) 2 HOMO LUMO 1 H2Pc/Ag(111) Bias U (V) Figure S1: Spectroscopy curve of an intact H2 Pc-molecule (stabiliziation parameters: U = 1.5 V; I = 1 na; Umod = 4 mv). Topography (b) and di /du -map (c) taken at a bias of U = 1.3 V shows the spatial distribution of the HOMO. Topography (d) and di /du -map (e) taken at a bias of U = 0.7 V shows the spatial distribution of the LUMO. [scan paramters (b)-(e): I = 1 na; Umod = 10 mv] spatially and energetically localized, the LUMO is distributed over the whole molecule and energetic broaden which indicates a strong hybridization of this orbital with the substrate. The step like increase of the di /du -signal at U = 0.8 V is very likely based on the fact that due to tautomerization processes the average topographic height is changed leading to an higher current signal and an higher di /du -signal of the Lock-In amplifier. This statement is further supported by the current signal (not shown) which has a jump at the bias voltage and not a change of slope as it would be expected for an IETS-signal. Experimental data for positive bias voltage The manuscript is mainly based on data taken at negative bias voltages. In this chapter, we will show that similar trends are observed for positive bias voltages. In Fig. S2 the current dependency for an intact H2 Pc-molecule is presented. The data shows that similar to the results of the negative bias voltage the exponent of the fit in the case of U = 0.6 V and U = 0.9 V is roughly one in the low current regime (I < 5 na) indicating that the excitation is based on a single electron process. For higher currents (I > 5 na) the exponent changed S2

3 rate f (Hz) Current I (na) bias: 0.6 V fit 1: 0.6 V fit 2: 0.6 V bias: 0.9 V fit: 0.9 V Figure S2: Current dependency for the intact H 2 Pc-molecule at a bias voltage of U = 0.6 V and U = 0.9 V, which is fit with power laws. For the first mentioned data set two power law fits were used as the exponent is changing for higher current values. The fit for the U = 0.9 V data set (green line) results in an exponent of 0.94 ± In the case of the U = 0.6 data set, the fit in the lower current regime (blue line) results in an exponent of (1.05 ± 0.12) and in the high current regime (olive) an exponent of (1.45 ± 0.09). to 1.45 ± Similar to the data of Fig. 3 in the main article, Fig. S3 shows the spatial distribution of the switching parameters probed at a bias of U = 0.8 V. The data shows qualitatively the same results as presented for negative bias voltage. Subtle changes are due to the different topography of the H 2 Pc-molecule probed at positive bias, which affects the appearance of the difference image [cf. Fig. S3 (b)] and the spatial distribution of the proportion of time staying in the high state [cf. Fig. S3 (d)]. Nevertheless, the spatial distribution of the switching frequency [cf. Fig. S3 (c)] and the spatial distribution of the proportion of time staying in configuration A [cf. Fig. S3 (e)] is qualitatively the same as in the case of negative bias voltages. In Fig. S4 (a) the topography of a dehydrogenated H 2 Pc-molecule and in Fig. S4 (b)- (d) spatial information of the switching parameters are presented taken at a bias voltage of U = 0.3 V. Whereas the spatial distribution of the proportion of time staying in the high or the low state [cf. S4(d)] is similar to the data taken at negative bias voltages, the spatial distribution of the switching rate is almost uniformly distributed over the molecule. This S3

4 is in contrast to the data taken at U = 0.3 V. The difference can likely be attributed to the LUMO, which is energetically close to U = 0.3 V (not shown), which could enhances the switching rate on the molecular frame off the center due to resonant electronic excitation. In Fig. S5 the bias dependent lifetime τ of the stable and metastable state of the dehydrogenated H 2 Pc-molecule is shown. Like in the case of negative bias voltages, the lifetime of the stable state continuously increases with decreasing bias voltage, whereas it is almost constant in the case of the metastable state. S4

5 (a) (b) 15 pm 1 nm -16 pm (c) 0.2 Hz (d) 99 % 0.0 Hz 1 % (e) 98.4 % 0.0 % Figure S3: (a) Topography of a pixel grid (grid parameters: U = 0.8 V and I = 1 na). Each pixel shows the average height of a 162 s time trace. (b) Difference image of the two configuration A and B. In the area of red regions the topographic height of configuration A is higher than of B, vice versa for the blue regions. (c) Spatial mapping of the tautomerization rate, showing that tautomerization can be induced all over the molecular frame, with the highest efficiency in the center of the molecule. (d) Spatial distribution of the proportion of time staying in the high-state. (e) With the help of the spatial information of (b) and (d), the spatial distribution of the proportion of time staying in the configuration A was extracted. S5

6 (a) (b) (c) 0.22 Hz (d) 99 % 1 nm 0.4 nm 0.02 Hz 3 % Figure S4: (a) Topographic images of a dehydrogenated H 2 Pc molecule. (b) Topography of a pixel grid (grid parameters: U = 0.3 V, I = 1 na). (c) Spatial distribution of the tautomerization rate. (d) Spatial distribution of the proportion of time staying in the high or the low state extracted from the time traces of the grid measurement. 100 lifetime t (s) stable state metastable state Bias U (V) Figure S5: The bias dependent lifetime τ shows an increased life time of the stable state with decreasing electron energy, whereas it is almost constant in the low energy regime of the metastable state. S6