Zone‐Sectored Organic Crystals with Spatially Resolved Exciton Dynamics

Among the organic semiconductors, rubrene stands out in terms of hole mobility, luminescence yield and exciton migration distance. A novel type of rubrene microcrystal is prepared in the orthorhombic phase, exhibiting zone‐sectored tabular domains with distinct photoluminescence (PL) characteristics. These sectors exhibit distinct photoluminescence spectra and time‐evolution, arising from differences in the in‐plane orientation of the orthorhombic unit cell relative to the crystal surface. Spatially resolved photoluminescence spectroscopy reveals that the redshifted 650 nm emission band has polarisation along the transition dipole moment and is associated with high photon absorption due to the alignment of excitation polarisation and transition dipole moment and selectively localized within specific sectors of the crystal. The detected photons originate from the direct emission of a geminate coherent triplet pair, or from its fusion. This band exhibits pure mono‐exponential dynamics with 3.7 ns lifetime. The triplet fusion behavior in the succeeding time regimes can be treated in the framework of power law scaling and a random walk. The emission kinetics are modeled using rate equations describing geminate and non‐geminate exciton fusion processes, enabling a quantitative interpretation of the spatially resolved photoluminescence kinetics. These findings introduce a material‐based strategy, opening novel routes for photonic applications and light harvesting.