Intramolecular motion in the solid state can be tailored to occur from kHz to GHz rates by synthesizing organic molecules with dumbbell-like architectures. In the first part of the talk, recent advances that contribute to the understanding of segmental motion in crystals will be discussed. Those studies helped us to devise new ways to employ molecular rotation in order to obtain organic materials with modulated properties, i.e. solid state emission. Our interest in luminogenic organic compounds is based on their potential technological applications like sensors, biological probes and organic light-emitting diodes, among others. Strong fluorescence of organic molecules in the solid state is often related to the restriction of the intramolecular rotations upon crystallization that would otherwise occur in solution, a phenomenon known as Aggregation-Induced Emission (AIE). The second part of this presentation will feature our current efforts towards the synthesis of ?-conjugated molecules designed to present fast molecular reorientations in the solid state. Exploring the molecular dynamics in the crystals of this highly conjugated systems may help us to understand better the mechanism of the AIE phenomenon and to generate novel organic materials with controllable emission.