Development of new NIR exciplex systems based on a PDI derivative in solution

Abstract

Near-infrared (NIR) exciplexes in solution are developed using the highly soluble, thermally and photochemically robust perylene diimide derivative N,Nʹ-bis(ethylpropyl)perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) at concentrations where aggregation is negligible as an electron acceptor paired with pyrene (Py) or anthracene (Ant) donors. This approach yields broad NIR exciplex emission extending to approximately 1000 nm. Steady-state spectroscopy in non-polar toluene shows efficient quenching of EP-PDI’s locally excited emission (540 nm) and confirms exciplex formation, with emission wavelength dependent on the donor’s HOMO energy level (Ant > Py). Time-resolved spectroscopy reveals the coexistence of locally excited and exciplex states, with the exciplex lifetime decreasing as donor concentration increases, attributed to thermally driven non-radiative dissipation in fine aggregates. Density functional theory (DFT) calculations indicate favorable HOMO/LUMO alignment for charge transfer, while TD-DFT simulations support exciplex geometries with face-to-face distances of 3.3–3.5 Å and NIR emission profiles. The branched-chain structure and high solubility of EP-PDI, optimized at 4 μM concentration, effectively suppress aggregation and interfacial defects that are common in solid-state systems. This solution-phase design provides a promising foundation for NIR exciplexes in optoelectronic applications such as OLEDs and OPVs as well as phototherapy. Future directions to extend exciplex lifetimes include optimizing solvent viscosity, employing peptoid-based donor-acceptor linkages, and using alkyl chains as linkers between donor and acceptor molecules, which may enhance magnetic field effects and device stability. The integration of experimental and computational insights underscores the potential of stable PDI derivatives for advancing solution-phase exciplex systems.