Photoconductance from the Bent-to-Planar Photocycle between Ground and Excited States in Single-Molecule Junctions

Single-molecule conductance measurements for 9,14diphenyl-9,14-dihydrodibenzo[a,c]phenazine (DPAC) may offer unique insight into the bent-to-planar photocycle between the ground and excited states. Herein, we employ DPAC derivative DPAC-SMe as the molecular prototype to fabricate single-molecule junctions using the scanning tunneling microscope break junction technique and explore photoconductance dependence on the excited-state structural/ electronic changes. We find up to similar to 200% conductance enhancement of DPAC-SMe under continuous 340 nm light irradiation than that without irradiation, while photoconductance disappears in the case where structural evolution of the DPAC-SMe is halted through macrocyclization. The in situ conductance modulation as pulsed 340 nm light irradiation is monitored in the DPAC-SMe-based junctions alone, suggesting that the photoconductance of DPAC-SMe stems from photoinduced intramolecular planarization. Theoretical calculations reveal that the photoinduced structural evolution brings about a significant redistribution of the electron cloud density, which leads to the appearance of Fano resonance, resulting in enhanced conductance through the DPAC-SMe-fabricated junctions. This work provides evidence of bent-to-planar photocycleinduced conductance differences at the single-molecule level, offering a tailored approach for tuning the charge transport characteristics of organic photoelectronic devices.

Automated summary

The study investigates the photoinduced structural/ electronic changes on the photoconductance of DPAC derivative DPAC-SMe using single-molecule junctions. The experiment reveals a significant enhancement of conductance under continuous 340 nm light irradiation, which is attributed to photoinduced intramolecular planarization. Theoretical calculations suggest that the redistribution of electron cloud density results in enhanced conductance through the DPAC-SMe junctions.