Abstract
pi-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 pi-stacking of zinc(II) porphyrin, [Zn-2], as a slipped dimer acceptor using a BODIPY unit, [bod], as the donor, bridged by the linker C6H4C equivalent to CC6H4. The rate of singlet energy transfer, k(ET)(S-1), at 298 K (k(ET)(S-1) = 4.5 X 10(10) s(-1)) extracted through the change in fluorescence lifetime, tau(F), of [bod] in the presence (27.1 ps) and the absence of [Zn-2] (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 pi-stacking effect exists (i.e., monoporphyrin units). At 77 K, the tau(F), of [bod] increases to 45.3 ps, indicating that k(ET)(S-1) decreases by 2-fold (2.2 X 10(10) 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.
