RGB photoluminescence from single-component hydrocarbon single-crystals: Revealing excited-state dynamics in organic semiconductors

The development of single-component organic materials that exhibit tunable red, green and blue (RGB) luminescence under ambient conditions can pave the way of materials with tailored photophysical properties. The optical behavior of such organic materials is largely determined by their excited-state dynamics of the excitons, which are formed when electrons are excited in the material. The excited-state dynamics of an organic molecules can be sensitively tuned, where even marginal variations in crystal morphology and molecular arrangement can drastically modify their optical behavior. Herein, we report a discovery of π-conjugated single-component system that can exhibit the RGB emission. This was realized by altering the morphological crystal dimensionality of a highly tunable single-component hydrocarbon coronene molecule in a single-step crystallization processes into 1D wire, 2D plate, and 3D rod, without introducing additional components or varying external stimuli. Time-resolved photoluminescence (PL) and transient absorption spectroscopy revealed the excited-state absorption (ESA) and self-trapped exciton (STE) formation in the excited electrons in 1D wire crystal plays a key role in emission color change from blue to green. Furthermore, static PL and absorption spectroscopy and single-crystal XRD revealed the dimerization of coronene results in significant reduction of optical band-gap energy and red shift into red emission band. We elucidated the complex relationship between excited-state dynamics and crystal structure of the coronene crystals. Our work presents a novel strategy for tuning the optical properties of single-component organic materials through crystal engineering, offering new possibilities for the development of advanced organic semiconducting devices.