Diketopyrrolopyrroles (DPPs) have attracted attention for their potential applications in organic photovoltaics due to their tunable optical properties and charge-carrier mobilities. In this study, we investigate the excited-state dynamics of a DPP dimer using time-dependent density functional theory (TDDFT) and nonadiabatic molecular dynamics simulations. Our results reveal a nearbarrierless hydrogen migration state intersection that facilitates ultrafast internal conversion with a lifetime of about 400 fs, leading to fluorescence quenching. Electronic density analysis along the relaxation pathway confirms a hydrogen atom transfer mechanism. These findings highlight the critical role of state intersections in the photophysical properties of DPP dimers, providing new insights for the design of functionalized DPP systems aimed at suppressing nonradiative decay for enhanced performance in photovoltaic applications.

As the demand for renewable energy continues to rise, organic photovoltaic (OPV) materials have garnered significant attention due to their tunable properties and cost-effectiveness. 1 Among these materials, diketopyrrolopyrroles (DPPs; Figure 1) stand out for their versatility, ease of functionalization, and strong absorption characteristics. 2 DPP-based systems have demonstrated promising power conversion efficiencies in OPVs. Yet their full potential remains limited by certain photophysical behaviors, particularly related to nonradiative decay pathways. Addressing these limitations requires a deeper understanding of the excited-state dynamics of DPPs at the molecular level.

DPP and its derivatives have been used as dyes due to their strong absorption and facility to increase the conjugation length due to functionalization. They also exhibit remarkable photophysical