Covalently linked perylenetetracarboxylic diimide dimers and trimers with rigid J-type aggregation structure

Covalently linked perylenetetracarboxylic diimide (PDI) dimers (D-1 and D-2) and trimers (T-1 and T-2) with slipped face-to-face stacked structure are prepared and their molecular structures are characterized by H-1 NMR, MALDI-TOF mass spectroscopy and elemental analysis. The rigid molecular structures of these compounds make it easier to establish a direct correlation between the aggregate structure and the photophysical properties. The minimized molecular structures of these compounds reveal that they are all face-to-face stacked aggregates with large longitudinal displacement. Their absorption spectra show red-shifted bands, suggesting the presence of J type excitonic coupling between the PDI subunits in these compounds. However, their steady state and time resolved fluorescence spectra revealed that the emission from the excimer-like states dominates the fluorescence of these compounds, this is similar to that of H-type aggregates and may be ascribed to the face-to-face stacked structure. In the fluorescence spectra of these compounds, a minor J-type emission can be identified for the compounds with a relatively large longitudinal displacement. An increase in the number of subunits in one aggregate from 2 to 3 also brings about distinctive changes in their photophysical properties, which can be ascribed to the changes in the stacking structure caused by the steric hindrance,