Beyond Structural Design: Reaction Trajectories as a Discovery Variable for CHONPS Covalent Matter: Perspective

Abstract

Modern materials chemistry is highly effective at designing predefined structures, but target-driven strategies necessarily explore only structures that can be specified in advance. This Perspective proposes a complementary discovery framework in which reaction history is treated as a controlled search variable rather than solely as a route to an intended product. C, H, O, N, P and S define a deliberately bounded model space, termed CHONPS space, for examining whether persistent covalent materials can be reached through distinct time-ordered trajectories from the same experimentally defined initial state. The framework does not introduce a new physicochemical principle; it operationalises established path dependence by fixing the initial state X, varying the reaction trajectory Γ, and testing for reproducible divergence among persistent material outcomes. Minimal experimental sets compare operations A, B, AB, BA and A+B while controlling cumulative exposure and other relevant variables. Evidence is strongest when compositionally comparable outcomes differ reproducibly in connectivity or organisation and, where relevant, in function. Persistence is distinguished from stability, and candidate states require subsequent definition of their stability domains. In situ and operando characterisation, multimodal analysis, automation and self-driving laboratories provide practical tools for mapping such trajectories and retaining both positive and negative outcomes. CHONPS is therefore presented as a model space for asking which persistent states become experimentally accessible when the final material is not predetermined and reaction history itself is used as a discovery variable.