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

Abstract

Covalently linked perylenetetracarboxylic diimide (PDI) dimers (D1 and D2) and trimers (T1 and T2) with slipped “face-to-face” stacked structure are prepared and their molecular structures are characterized by 1H 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.

Photophysical Properties of Perylenetetracarboxylic Diimide Dimers with Slipped “Face-to-Face” Stacked Structure and Different Bay Substitutions

“…Two absorption bands at about 549 nm and 515 nm are observed in the absorption spectrum of dimer 5. The maximal absorption band is red-shifted by about 10 nm compared with that of monomer 1 [10].…”

“…And Wasielewski group has reported three covalently linked core-unsubstituted PDI dimers with slipstacked structure [9]. In addition, a series of covalently linked core-substituted PDI dimers and trimers with diphenoxyl groups have also been reported by our group [10]. In both of these studies, the degree of slipping of the two PDI chromophores is tuned by changing the spacer, which can affect the photophysical property of J-aggregate.…”

“…An emission band at about 584 nm is observed in the emission spectrum of dimer 5, which red-shifted by 15 nm compared with that of monomer 1. According to the previous report, the emission of dimer 4 and 5 can be attributed to the "excimer-like" states [10]. It is worth noting that the emission from "excimer-like" states of PDI varied dramatically for PDI dimers with different stacked structures.…”

“…Compounds 1-5, 10-13 were prepared following the published procedures [10] [12]- [16]. All other chemicals are purchased from commercial source and used as received without further purification.…”

Conformational analysis of diols: Role of the linker on the relative orientation of hydroxyl groups

“…Similarly, covalently linked dimers were synthesized to investigate J‐ and H‐type aggregates . For example, a series of slip‐stacked perylene‐diimide dimers were prepared using linkers composed of the xanthene moiety, and longitudinal displacement groups composed of phenyl‐acetylides were used to investigate the effects of slip‐stacking on the degree of excitonic coupling …”