S. Prathapan et al., Synthesis and excited-state photodynamics of perylene-porphyrin dyads. 1. Parallel energy and charge transfer via a diphenylethyne linker, J PHYS CH B, 105(34), 2001, pp. 8237-8248
The photophysical properties of a perylene-porphyrin dyad have been examine
d with the aim of using this construct for molecular photonics applications
. The dyad consists of a perylene-bis(imide) dye (PDI) connected to a zinc
porphyrin (Zn) via a diphenylethyne linker (pep). In both polar and nonpola
r solvents, the photoexcited perylene unit (PDI*) decays very rapidly (life
times of 2.5 (toluene) and 2.4 ps (acetonitrile)) by energy transfer to the
porphyrin, forming PDI-pep-Zn* in high yield (80%, toluene; 70% acetonitri
le), and hole transfer to the porphyrin, forming PDI--pep-Zn+ in lesser yie
ld (20%, toluene; 30% acetonitrile). In both toluene and acetonitrile, the
Zn* excited state subsequently decays with a lifetime of 0.4 ns primarily (
80%) by electron transfer to the perylene (forming PDI--pep-Zn+). In the no
npolar solvent (toluene), the PDI--pep-Zn' charge-transfer product has a li
fetime of > 10 ns and decays by charge recombination primarily to the groun
d state but also by thermal repopulation of the Zn* excited state. The occu
rrence of the latter process provides a direct experimental measure of the
energy of the charge-separated state. In the polar solvent (acetonitrile),
the PDI--pep-Zn' charge-separated state decays much more rapidly (<0.5 ns)
and exclusively to the ground state. In general, the complementary perylene
and porphyrin absorption properties together with very fast and efficient
PDI*-pep-Zn --> PDI-pep-Zn* energy transfer suggest that perylenes have sig
nificant potential as accessory pigments in porphyrin-based arrays for ligh
t-harvesting and energy- transport applications. Furthermore, the finding o
f fast energy transfer initiated in PDI*, charge-transfer reactions that ca
n be elicited either in PDI* or Zn*, and a charge-separated state (PDI--pep
-Zn') that can be long- or short-lived depending on solvent polarity, indic
ates the versatility of the perylene-porphyrin motif for a variety of appli
cations in molecular photonics.