The past six years have witnessed the rapid growth of interest in Dion–Jacobson (DJ) phase two-dimensional (2D) hybrid halide perovskitesas optoelectronic materials with considerable intrinsic stability. The precise relationships between structural variations and the resultingcharge carrier dynamics at finite temperature in these materials are keys to practical applications and are not yet completely understood.Here, we study 3-(aminomethyl) piperidinium (3AMP) and 4-(aminomethyl) piperidinium (4AMP) spacer cation-based lead iodide DJphase systems and find these spacer cations to have a profound impact on the structural dynamics. Particularly, large conformational dynamicsof the 3AMP-based perovskite compared to that of the 4AMP at room temperature leads to pronounced state energy fluctuation nearband edges and further results in a shorter quantum coherence. The faster quantum decoherence of the 3AMP spacer-based perovskiteunderpins a longer nonradiative lifetime, offering insight into its superior performance as an optoelectronic material. This work sheds lighton the relationship between structural fluctuations and charge carrier dynamics that can help in designing 2D perovskites with superior photophysicalproperties.