This study investigates the ultrafast electronic relaxation pathways of the molecular photoswitch quadricyclane (QC) after ultraviolet (UV) excitation. Using time-resolved gas-phase extreme ultraviolet (XUV) photoelectron spectroscopy (TRPES) combined with non-adiabatic molecular dynamics simulations, the researchers identify two competing relaxation pathways: a fast pathway (<100 fs) involving effective coupling to valence electronic states, and a slow pathway involving initial motions across Rydberg states and taking several hundred femtoseconds. Both pathways facilitate interconversion between QC and its isomer norbornadiene (NBD), with the fast pathway leading to a 3:2 branching ratio of NBD to QC products upon returning to the electronic ground state. The photoswitching of QC and NBD is significant for applications in catalysis, photochromic materials, molecular machines, logic devices, and energy storage, particularly in molecular solar thermal (MOST) systems. The study reveals that the fast pathway involves a strong coupling between Rydberg and valence states, while the slow pathway involves a transition through Rydberg states before relaxing to the ground state. The results highlight the importance of non-adiabatic couplings and conical intersections in the relaxation dynamics, providing insights into the molecular mechanisms underlying the ultrafast isomerization. The findings demonstrate the utility of TRPES with XUV probes in characterizing complex photochemical mechanisms. The study also suggests that the properties of the photoswitch can be manipulated through substituent groups, spatial confinement, and excitation wavelength. These insights could lead to the development of more efficient MOST systems and a deeper understanding of ultrafast ring reconfigurations in photoswitch molecules. The results are supported by high-level electronic structure calculations and simulations, confirming the experimental observations and providing a detailed picture of the relaxation pathways involved.This study investigates the ultrafast electronic relaxation pathways of the molecular photoswitch quadricyclane (QC) after ultraviolet (UV) excitation. Using time-resolved gas-phase extreme ultraviolet (XUV) photoelectron spectroscopy (TRPES) combined with non-adiabatic molecular dynamics simulations, the researchers identify two competing relaxation pathways: a fast pathway (<100 fs) involving effective coupling to valence electronic states, and a slow pathway involving initial motions across Rydberg states and taking several hundred femtoseconds. Both pathways facilitate interconversion between QC and its isomer norbornadiene (NBD), with the fast pathway leading to a 3:2 branching ratio of NBD to QC products upon returning to the electronic ground state. The photoswitching of QC and NBD is significant for applications in catalysis, photochromic materials, molecular machines, logic devices, and energy storage, particularly in molecular solar thermal (MOST) systems. The study reveals that the fast pathway involves a strong coupling between Rydberg and valence states, while the slow pathway involves a transition through Rydberg states before relaxing to the ground state. The results highlight the importance of non-adiabatic couplings and conical intersections in the relaxation dynamics, providing insights into the molecular mechanisms underlying the ultrafast isomerization. The findings demonstrate the utility of TRPES with XUV probes in characterizing complex photochemical mechanisms. The study also suggests that the properties of the photoswitch can be manipulated through substituent groups, spatial confinement, and excitation wavelength. These insights could lead to the development of more efficient MOST systems and a deeper understanding of ultrafast ring reconfigurations in photoswitch molecules. The results are supported by high-level electronic structure calculations and simulations, confirming the experimental observations and providing a detailed picture of the relaxation pathways involved.