Appending Coronene Diimide with Carbon Nanohoops Allows for Rapid Intersystem Crossing in Neat Film

Abstract

The development of innovative triplet materials plays a significant role in various applications. Although effective tuning of triplet formation by intersystem crossing (ISC) has been well established in solution, the modulation of ISC processes in the solid state remains a challenge due to the presence of other exciton decay channels through intermolecular interactions. The cyclic structure of cycloparaphenylenes (CPPs) offers a unique platform to tune the intermolecular packing, which leads to controllable exciton dynamics in the solid state. Herein, by integrating an electron deficient coronene diimide (CDI) unit into the CPP framework, a donor−acceptor type of conjugated macrocycle (CDI−CPP) featuring intramolecular charge−transfer (CT) interaction was designed and synthesized. Effective intermolecular CT interaction resulting from a slipped herringbone packing was confirmed by X−ray crystallography. Transient spectroscopy studies showed that CDI−CPP undergoes ISC in both solution and the film state, with triplet generation time constants of 4.5 ns and 238 ps, respectively. The rapid triplet formation through ISC in the film state can be ascribed to the cooperation between intra− and intermolecular charge−transfer interactions. Our results highlight that intermolecular CT interaction has a pronounced effect on the ISC process in the solid state.

Symmetry-Breaking Charge Separation Mediated Triplet Population in a Perylenediimide Trimer at the Single-Molecule Level

“…Whereas, in nonpolar TOL and PS, triplet states are largely generated via the CT state. 23,71,72 In summary, we have synthesized a PDI-based rigid trimer, PDI-T, exhibiting symmetry-breaking charge separation mediated triplet population upon photoexcitation. Fragmentbased excited-state analysis provides evidence for the occurrence of CT states in the PDI-T trimer.…”

“…30,70 The CT state (component (B)) decays within 2.75 ns, forming component (C) in the EAS spectra (Figure 4a-bottom). Component (C) is a long-lived species and could be due to the population of triplet states in PDI-T. 71,72 The EAS spectra of PDI-T in THF and ACE showed distinct evidence of forming the CSS (component (B)) through ultrafast CS from the initially populated locally excited singlet state (component (A)) with time constants of 5.3 and 3.7 ps, respectively (Figures 4b-bottom, 4c-bottom and S28). 73 Ultrafast CS observed in PDI-T in the presence of polar dielectric environments could have originated from the lowering of the CSS energies relative to the 1 PDI-T* state energy.…”

“…PDI-T populates triplet excited-states via CR from the CSS in polar dielectrics like THF, ACE, and PVA. Whereas, in nonpolar TOL and PS, triplet states are largely generated via the CT state. ,, …”

“…17 The slower CT recombination could be the probable reason for the higher ϕ T in PDI-T in nonpolar TOL. 23,71,72 A schematic Jablonski diagram summarizing the mechanism of the triplet excited-state population in PDI-T upon photoexcitation in different dielectrics is shown in Figure 5. PDI-T populates triplet excited-states via CR from the CSS in polar dielectrics like THF, ACE, and PVA.…”

“…The CT state corresponds to incomplete or partial charge separation, whereas complete charge separation between donor and acceptor moieties creates a CSS. − The observation of a CT state instead of a CSS in the excited-state dynamics of PDI-T in TOL could be due to the higher energy of the CT state under the influence of a less polar dielectric medium. , The CT state (component (B)) decays within 2.75 ns, forming component (C) in the EAS spectra (Figure a-bottom). Component (C) is a long-lived species and could be due to the population of triplet states in PDI-T . , …”