We focus on the design and synthesis of organic functional materials with optimized structure-property relationships for energy and biomedical applications. By fine-tuning the radiative and non-radiative decay pathways, we produce materials with optimized optical or photothermal performance. Further adjusting the energy gap between the lowest triplet state and the lowest singlet state facilitates intersystem crossing, which yields photosensitizers or phosphorescent molecules. Of particular interest are the molecules with aggregation-induced emission, which show negligible fluorescence as molecular species, but can be induced to show high fluorescence in the aggregate state. Our recent discovery of a doping system opens a new opportunity for realizing ultralong phosphorescence.