## 3 Results and Discussion
The blink lifetime is the highest for the low-bias regime, reaching 0.73 s, decreasing to 0.44 s for HC and 0.58 s scores for LC at intermediate Vbias and the shortest blink lifetimes, of 0.32 s for HC and of 0.42 s for LC, at high Vbias. The decrease in blink lifetime with increasing Vbias can be explained by a decrease in junction stability due to local heating effects and electmigration-induced mobility of metal atoms under higher EEFs. [54]. Note that at all the applied bias voltages, HC blinks display a 1.3 times longer lifetime as compared to LC blinks, which denotes an intrinsically higher junction stability in the case of HC junctions. The relative populations of the HC and LC junctions display a clear dependence on the applied EEFs. At low bias, all detected blinks correspond to the HC regime while at intermediate and high biases, the HC yield decreases significantly but LC features increase. At Vbias = 65 mV, the LC/HC yield ratio is nearly one to one, 48 /52, respectively. At Vbias = 130 mV, the LC/HC yield ratio increases to more than three, with the LC yield reaching 77 % of the total captured blinks. The observed behaviour in the blinking BJ approach is in accordance with the dynamic BJ results. In dynamic BJ experiments the varying gap distances produce overall higher EEFs even at the lower Vbias due to the transiently lower electrode-electrode gap distances (starting at direct electrode contact in the break-junction cycle, Figure 1c), which are sufficiently strong to induce the in situ _trans_-to-_cis_ isomerisation and resulting in observed larger LC (_cis_-TMC) yields than in the blinking experiments. The observations for both BJ approaches suggest a conversion of HC to LC regimes in the presence of a sufficiently large Vbias, i.e., a sufficiently strong applied EEF. To test the HC to LC switching hypothesis, we perform voltage-pulse experiments where a high bias voltage pulse of 300 mV is applied for 10 ms during the lifetime of a HC blink to induce the switching to LC (Appendix A, Figure A1). After the voltage pulse, the junction switches from HC to LC and stays at the characteristic LC value at the returning low Vbias of 30 mV prior to junction breakdown. Analogous voltage-jump experiments performed during LC blinks, show no conversion from LC to HC values. Both sets of experiments attest an irreversible process for the HC-to-LC conversion. What is the nature of the two distinct Vbias-dependent conductance features for _trans_-TMC in Figure 3? The static BJ results rule out a mechanical origin of the observed conductance switching initially observed in the dynamic BJ experiments, and point toward the bias voltage as the driving force for the observed bimodal conductance behaviour. Guided by previous literature that showed isomerisation reactions of individual molecules tuned by voltage differences [52; 55], we hypothesize that applying a Vbias to the TMC junction induces a _trans_-to-_cis_ isomerisation of the molecule in the junction [52]. We have synthesized a homologous _cis_ carotenoid (_cis_-TMC-syn) with a nearly identical structure (Figure 1b) and use it as a control test. The _cis_-TMC-syn control junctions show identical yield, conductance and blinking lifetime as the LC regime observed for the _trans_-TMC junctions (see Appendix A.4 for details). These control findings strongly support our hypothesis that the _trans_-TMC undergoes an in situ isomerisation induced by the applied EEF along the junction. The observed irreversibility of the isomerisation can be explained by preferential molecule \(\mid\) electrode coupling of the _cis_-TMC compared to _trans_-TMC [9]. We speculate that the _cis_-TMC structure offers an increased coupling between the distal phenyl ring and the Au electrode through van-der-Waals (\(\pi\)-) interactions [56; 57].