Sample-based Quantum Diagonalization Methods for Modeling the Photon-excited States in Diazirine and Diazo Compounds

Diazirines and diazo compounds are versatile photoreactive precursors for generating carbenes, which serve as key intermediates in chemical biology, photochemistry, and materials science. Accurately modeling their photochemical reaction pathways remains computationally challenging due to the large active spaces required and the need to capture excited-state potential energy surfaces. In this work, we present a hybrid quantum–classical framework for investigating carbene formation in representative diazirine–diazomethane systems. The approach employs Sample-Based Quantum Diagonalization (SQD) and its extended variant (Ext-SQD) to characterize the ground and excited states, respectively. Quantum computations were performed on superconducting quantum processors and benchmarked against high-level classical methods with basis set cc-pVTZ, including DFT, CCSD, CASCI, and SCI. SQD achieved accuracy surpassing the chemical accuracy threshold for nearly all stationary points on the parent diazirine potential energy surface relative to the CASCI(12,10) reference. Moreover, SQD results closely follow CASCI and SCI trends across all photochemical pathways. These findings underscore the potential of sample-based quantum diagonalization methods as scalable and accurate tools for modeling photon-induced excitations and reaction dynamics in electronically complex molecular systems.