From reproducibility to comparability in computational photochemistry: lessons from the PhotoChem explorer prototype.

We present the PhotoChem Explorer (PCE) prototype, a proof-of-concept web-based platform that represents computational photochemistry studies of gas-phase molecules in a structured and queryable form. Rather than treating excited-state dynamics simulations as isolated results reported in heterogeneous formats and across different sources, PCE organizes studies according to their molecular systems, computational workflows, methodological choices, and associated observables, facilitating that relationships and trends can be explored systematically across studies. In this way, the prototype illustrates how structured data representations could support improved findability, comparison, reproducibility, and reuse in computational photochemistry. At a fundamental level, it demonstrates how excited-state dynamics studies could become part of a more connected and cumulative body of knowledge, potentially enabling new modes of investigation. The prototype exposes practical challenges that must be addressed to realize this vision, including the development of shared representations, workflow descriptions, and their integration into scientific practice. More broadly, PCE is intended as a practice-driven experimentation platform to stimulate discussion and iterative community development of standards and representations for excited-state dynamics studies.