Intramolecular interchromophore singlet-singlet and triplet-singlet energy transfer in a metal-free donor-acceptor emitter

In this work we demonstrate the occurrence of singlet to singlet, and triplet to singlet, intramolecular energy transfer between two thiophene-comprising donors (D) and a central perylene bisimide acceptor (A) covalently linked to each other trough a linker that separates the donor and acceptor moieties in a D-A-D structure. The designed metal-free organic tandem luminophore is herein designated as ARC-1467. Energy transfer from the excited triplet state of the thiophene donor to the singlet state of the perylene bisimide acceptor is observed in solution and in solid films of ARC-1467 dispersed in polystyrene. When the perylene bisimide acceptor is directly excited, the fluorescence decays with 4.9 ns lifetime. However, upon excitation of the donor unit in the near-UV region, delayed fluorescence of perylene bisimide with 5.7 μs lifetime is distinctly observed demonstrating the occurrence of energy transfer from the triplet state of the D unit to the perylene bisimide acceptor