Energy Flow Dynamics within Cofacial and Slip-Stacked Perylene-3,4-dicarboximide Dimer Models of π-Aggregates

Abstract

Robust perylene-3,4-dicarboximide (PMI) π-aggregates provide important light-harvesting and electron-hole pair generation advantages in organic photovoltaics and related applications, but relatively few studies have focused on the electronic interactions between PMI chromophores. In contrast, structure-function relationships based on π-π stacking in the related perylene-3,4:9,10-bis(dicarboximides) (PDIs) have been widely investigated. The performance of both PMI and PDI derivatives in organic devices may be limited by the formation of low-energy excimer trap states in morphologies where interchromophore coupling is strong. Here, five covalently bound PMI dimers with varying degrees of electronic interaction were studied to probe the relative chromophore orientations that lead to excimer energy trap states. Femtosecond near-infrared transient absorption spectroscopy was used to observe the growth of a low-energy transition at ~1450-1520 nm characteristic of the excimer state in these covalent dimers. The excimer-state absorption appears in ~1 ps, followed by conformational relaxation over 8-17 ps. The excimer state then decays in 6.9-12.8 ns, as measured by time-resolved fluorescence spectroscopy. The excimer lifetimes reach a maximum for a slip-stacked geometry in which the two PMI molecules are displaced along their long axes by one phenyl group (~4.3 Å). Additional displacement of the PMIs by a biphenyl spacer along the long axis prevents excimer formation. Symmetry-breaking charge transfer is not observed in any of the PMI dimers, and only a small triplet yield (<5%) is observed for the cofacial PMI dimers. These data provide structural insights for minimizing excimer trap states in organic devices based on PMI derivatives.

Energy transfer and spectroscopic characterization of a perylenetetracarboxylic diimide (PDI) hexamer

“…12,35 Because the lower exciton band of the dimer is forbidden with less intense absorption transition from the ground state for an H-type structure, that as mentioned above, a low energy pre-associated excimer already exist below the lower-energy exciton state, where the relaxation from exciton state to the pre-associated excimer is very fast less than 4.5 ps or even more faster as reported previously, 36,45 and after an excitation, the excited state relaxation in the face-to-face dimer (H-type) will play a main role in excited PDI-hexamer, 42,45,46 while a sequential kinetic model is also appropriate for the global analysis of the timeresolved data of PDI-hexamer as predicted from Kasha model. 28 Althrough, the free dimer (see Figure S5) is not an ideal model for making comparison with the dimer in hexamer, several PDI-dimers with the similar face-to-face π-stacking geometry as the PDI-dimer in our PDI-hexamer have been reported, 17,38,45,46 where the spectral features and excited state dynamics observed in our PDI-hexamer are very similar to the behaviours observed in those reported PDI-dimers. Therefore, together with the conclusion from the steady-state measurements, the sequential scheme could be used for modeling the transient data of both monomer and hexamer, that is, EADS associated with certain kinetic profile represents the spectral features following that dynamics, the corresponding time constant can be regarded as the lifetime of each EADS.…”

“…37,42 Recently, Wasielewski and coworkers had investigated the energy flow dynamics and the excimer formation of cofacial PDI dimers. 45,46,48 They mentioned an 8-17 ps relaxation in the model which is assigned to geometric rearrangement from the initial unrelaxed excimer state to a more relaxed excimer conformation due to the existence of the displacement rotational angle between the long N-N axsis. 45 In our case, the PDI hexamer has a similar conformation (as shown in Scheme 2) so that the 7.9 ps component is attributed to the relaxation from the unrelaxed to a more relaxed excimer state.…”

Foldable glycoprobes capable of fluorogenic crosslinking of biomacromolecules

“…This suggests an intimacy between the two fluorophores. 26,27 Shown in Fig. S1b† are the stacked absorbance (A) and emission (E) spectra of P and N , implying a possibility of Förster resonance energy transfer (FRET) from P to N because of good overlap between the emission band of the former with the absorbance band of the latter.…”

Molecular Control of Internal Crystallization and Photocatalytic Function in Supramolecular Nanostructures

“…26 The strong propensity of rylene-based chromophores such as perylene diimide (PDI) and perylene monoimide (PMI) to π-π stack makes them ideal targets to investigate how molecular packing affects electronic properties in supramolecular systems. 7,20,27–29 One example from Adams et al . revealed photoconductivity of PDI thin films could be dramatically altered by controlling the extent of H and J aggregation of chromphores.…”