As detailed above, this contrasting behavior in small versus extended chromophores originates from differences in the relative importance of long-range interactions. Because of the larger nearest-neighbor interactions and the ensued increased excitonic bandwidth, the number of spatially extended states transiently accessible at room temperature from the bottom of the excitonic DOS is reduced in the 6-mer (compared to the 30-mer) stacks, see representative trajectories in Supplemental Figure . Including long-range interactions in the Hamiltonian for short polymer aggregates results in the formation of dynamic deep energy states (see Supplemental Figure ) that can act as trapping sites, explaining the decrease in . The presence of these deep trap states in short polymer stacks is further supported by calculations including non-local exciton-phonon couplings, which demonstrates larger improvement in compared to that in long polymer stacks (see Supplemental Figure ), suggesting thermal fluctuations of excitonic couplings are essential in the case of short polymer aggregates to transiently access spatially extended states.