Steric Control of Photocatalytic Electron Transfer: A Predictive Framework Using Sterimol Parameters.

Steric effects strongly influence excited-state electron transfer, yet accurately predicting their impact remains challenging. In this study, we quantified the steric bulk of 11 axial substituents on a silicon phthalocyanine photocatalyst using Sterimol parameters, and fluorescence-quenching experiments were performed with N,N-diisopropylethylamine to evaluate the influence of steric effects on electron-transfer efficiency. Multiparameter linear regression analysis revealed a correlation between the Sterimol parameters and the Stern-Volmer quenching constant (KSV), with distinct contributions from the Sterimol descriptors wB1, wB5, and wL. Among these descriptors, the minimum substituent width (wB1) was identified as the dominant steric parameter. Leave-two-out cross-validation demonstrated reasonable predictive performance within the branching catalyst subset, highlighting the potential of this Sterimol-based model to estimate KSV values for new structurally related silicon phthalocyanine photocatalysts. This work serves as a proof-of-concept for using Sterimol parameters to quantify steric effects in photocatalyst quenching and establish predictive structure-property relationships that may be extended to other photocatalyst classes.