Abstract
<title>Abstract</title> <p> Understanding the effect of organic spacers on the fundamental excited-state processes in 2D perovskites is crucial for advancing these novel materials. Mn doping offers a powerful strategy for tuning and enhancing the optoelectronic properties of halide perovskites, yet the role of spacers in Mn emission dynamics remains poorly understood. Herein, we investigate these processes in Mn-doped 2D Ruddlesden–Popper perovskite crystals with aromatic phenethylammonium (PEA) and aliphatic butylammonium (BA) spacers. Notably, PEA-based perovskites exhibit strong dopant emission with a photoluminescence quantum yield of 47%, compared to 15% for BA-based systems at the same doping level. To understand this contrast, we probed the structural dynamics and transient transport properties. We show that the enhanced Mn emission in PEA-based perovskites arises from the structural rigidity and reduced dynamic disorder imparted by the aromatic spacer, enabling efficient carrier transport. In contrast, the softer BA lattice exhibits stronger exciton–phonon coupling and greater dynamic disorder, resulting in slower exciton transport, faster nonradiative decay of Mn <sup>2+</sup> states, and consequently weaker Mn emission. This work provides a general framework for understanding spacer effects in 2D perovskites and guiding the design of advanced luminescent materials. </p>