High pressure up to 50 kbar generated in a diamond anvil cell has been applied to the investigation of organic molecules in their phosphorescent triplet state. Experimental techniques include specifically adapted optically detected magnetic resonance (Odmr) and optical spectroscopy. This paper reviews some of the high points of our results. On the microscopic scale there is no isotropic compression. Pressure enhances the interaction of a chromophore with its neighbours in a few specific modes according to crystalline packing. These interactions may shift the energy levels of the chromophore, or enhance the dynamical processes in the crystal. A variety of pressure-induced effects may be rationalized on this basis.