Arm‐Length‐Controlled CsPbBr ₃ Nanocrystals for Tunable Optical and Assembly Behavior

Colloidal cesium lead bromide (CsPbBr₃) nanocrystals (NCs) are excellent candidates for various photonic and optoelectronic applications due to their bright and stable green emission. Here, we establish arm length control as a central structural parameter that governs both the optical properties of individual CsPbBr₃ NCs and their self-assembly behavior. Armed NCs, featuring a cubic core with multiple protruding arms, are synthesized by controlling seed size, concentration, and injection temperature, while arm length is tuned via cesium oleate concentration. Prolonged storage in toluene is shown to lead to a time-dependent morphological evolution from armed NCs to 26-faceted rhombicuboctahedra, with short-armed structures as intermediates. NCs with a longer arm length yield enhanced radiative efficiency, extended photoluminescence (PL) lifetimes, and suppressed blinking, making such NCs suitable for light-emitting devices and quantum photonic applications. In contrast, short-armed NCs exhibit faster recombination, stronger PL intermittency, and increased surface accessibility, which are favorable for sensing and high-speed single-photon emission. The arm length also governs self-assembly behavior, hereby opening new possibilities for applications. Armed NCs form densely 3D-packed assemblies with tunable configurations. This work demonstrates how arm length tuning expands the functional potential of CsPbBr₃ NCs by linking morphological control to both optical response and self-assembly characteristics.