Difference in the Photophysical Properties of a Perylenetetracarboxylic Diimide Dimer and a Hexamer Linked by the Same Hexaphenylbenzene Group

Abstract

A perylenetetracarboxylic diimide hexamer (6PDI) and a dimer (2PDI) linked with the same hexaphenylbenzene group were prepared, and the structures were fully characterized by (1)H NMR spectroscopy, mass spectrometry, and elemental analysis. Due to the similar molecular structure of these two compounds, similar interactions between/among the PDI subunits as well as similar photophysical properties are expected. However, the stationary UV/Vis absorption spectra reveal that the interactions among/between the PDI subunits in 6PDI are significantly stronger than those in 2PDI. This can be attributed to blocked rotation along the long axis of the PDI subunits in 6PDI due to steric hindrance of the two neighboring PDI subunits. The stronger interactions among the PDI subunits in 6PDI lead to long-wavelength emission, which can be assigned to "excimer-like" excited states. A similar conclusion can also be deduced from the fluorescence quantum yields and the fluorescence lifetimes. Electrochemical studies revealed that interactions between/among the PDI subunits in both 2PDI and 6PDI are still in the range of weak interactions. Ultrafast transient anisotropy decay dynamics revealed that excitation delocalization between the PDI subunits within 2PDI and 6PDI is quick and efficient. More interestingly, delocalization is faster in 6PDI than in 2PDI, probably because of the stronger interactions among the PDI subunits in the former.

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.…”

“…For comparison, the molecular structures of the PDI-monomer and the PDI-dimer are also shown in Scheme 1. PDIs have been thoroughly studied in the last few years as active materials for light harvesting, [13][14][15][16][17] photovoltaic applications, 16,18,19 and as model chromophores exhibiting basic photoinduced charge and energy transfer processes, whose main characteristics are outstanding photostability and the ability to self-assemble in solution, mostly by p-p stacking. In the PDI-hexamer, as described in ref.…”

Excited‐State Deactivation of Branched Phthalocyanine Compounds

“…[10,11] In the past few years, the self-assembly of the organic chromo-phores has attractedw idespreada ttention, for example, the discoveryo ft he importance of the positiono fa ggregated chlorophyll molecules in purple bacteria in energy transfer in photosynthesis andt he study of excitation-energy transfers from monomeric subunits to dimerice xcimers in the artificial perylenetetracarboxylicd iimide (PDI) trimers ystem. [7,[12][13][14][15][16][17] These discoveries not only provide ag reat fundamental mechanism modelf or photosynthesis, but also novel ideas for the designa nd synthesis of various molecular self-assembly model systemsw ith fewer chromophores for potentiala pplications in organic photovoltaics.…”

Diels–Alder Cycloaddition with CO, CO2, SO2, or N2 Extrusion: A Powerful Tool for Material Chemistry

“…The same year, Xue and colleagues described DA cycloaddition and Co-catalyzed cyclotrimerization used in the syntheses of perylenetetracarboxylic diimide hexamer ( A ) and dimer ( B ) linked with the same hexaphenylbenzene core ( Scheme 105 ) [ 160 ].…”

“… Syntheses of HPB derivatives bearing two or six PBI-moieties via DA cycloaddition or Co-catalyzed cyclotrimerization, respectively [ 160 ]. Reagents and conditions: a = dioxane, [Co 2 (CO) 8 ], rfx, 12 h; b = Ph 2 O, rfx, 12 h; Y = 5% (for A ) or 4% (for B ).…”