Excitation energy transfer in novel acetylenic perylene diimide scaffolds

New perylene diimide (PDI) dimers (bis(PDI)s) with either tetraethynylethene (TEE) or 2,4-hexadiyne as the bridging unit were synthesized and the degree of intramolecular communication between the two PDI units was investigated as a function of the spacer unit and solvent polarity by absorption and emission spectroscopies, electrochemistry, and by atomic force microscopy (AFM). The experiments reveal that energy transfer occurs between TEE and PDI, and between PDI units. In the bis(PDI)-TEE system, flexible linkers allowed for intramolecular pi-pi stacking of the PDI chromophores in solution. The degree of stacking is solvent dependent, being more pronounced in non-polar solvents. The molecules were also found to self-assemble at a mica surface by intermolecular pi-pi interactions and to form fibrilar structures. Intermolecular excitation energy transfer was observed at the surface.