Is π‑Stacking Prone To Accelerate Singlet–Singlet Energy Transfers?

π-Stacking is the most common structural feature that dictates the optical and electronic properties of chromophores in the solid state. Herein, a unidirectional singlet–singlet energy-transfer dyad has been designed to test the effect of π-stacking of zinc­(II) porphyrin, [Zn₂], as a slipped dimer acceptor using a BODIPY unit, [bod], as the donor, bridged by the linker C₆H₄CCC₆H₄. The rate of singlet energy transfer, k_ET(S₁), at 298 K (k_ET(S₁) = 4.5 × 10¹⁰ s^–1) extracted through the change in fluorescence lifetime, τ_F, of [bod] in the presence (27.1 ps) and the absence of [Zn₂] (4.61 ns) from Streak camera measurements, and the rise time of the acceptor signal in femtosecond transient absorption spectra (22.0 ps), is faster than most literature cases where no π-stacking effect exists (i.e., monoporphyrin units). At 77 K, the τ_F of [bod] increases to 45.3 ps, indicating that k_ET(S₁) decreases by 2-fold (2.2 × 10¹⁰ s^–1), a value similar to most values reported in the literature, thus suggesting that the higher value at 298 K is thermally promoted at a higher temperature.