Antenna effects in truxene-bridged BODIPY triarylzinc(II)porphyrin dyads: evidence for a dual Dexter-Forster mechanism

The antenna process from an energy donor (BODIPY; 4',4'-difluoro-1',3',5',7'-tetramethyl-4'-bora- 3a',4a'-diaza-s-indacene) in its singlet state to two acceptors (two zinc(II) 5,15-p-tolyl-10- phenylporphyrin) bridged by a central truxene residue (5',5'',10',10'',15',15''-hexabutyltruxene), 5, has been analysed by means of comparison of the energy transfer rates with those of a structurally similar beta-substituted BODIPY-(zinc(II) 5,10,15-p-tolyl-porphyrin), 6, where no conjugation is present between the donor and the two acceptors using the Forster resonance energy transfer (FRET) approximation. It is estimated that the energy transfer in 5 operates mostly via a Dexter mechanism (>99%), and the remaining proceeds via a Forster mechanism (<1%). This information is useful for the design of future molecular devices aimed at harvesting light.