Design of Triads for Probing the Direct Through Space Energy Transfers in Closely Spaced Assemblies

Using a selective stepwise Suzuki cross-coupling reaction, two trimers built on three different chromophores were prepared. These hinters exhibit a D(boolean AND)A(1)-A(2) structure where the donor D (octa-beta-alkyl zinc(II)porphyrin either as diethylhexamethyl, 10a, or tetraethyltetramethyl, 10b, derivatives) through space transfers the S-1 energy to two different acceptors, di(4-ethylbenzene) zinc(II)porphyrin (A(1); acceptor 1) placed cofacial with D, and the corresponding free base (A(2); acceptor 2), which is meso-meso-linked with A(1). This structure design allows for the possibility of comparing two series of assemblies, 9a,b (D(boolean AND)A(1)) with 10a,b (D-boolean AND(A) over cap (1)-A(2)), for the evaluation of the S-1 energy transfer for the global process D*-> A(2) in the timers. From the comparison of the decays of the fluorescence of D, the rates for through space energy transfer, k(ET) for 10a,b (k(ET) approximate to 6.4 X 10(9) (10a), 5.9 X 10(9) s(-1) (10b)), and those for the corresponding cofacial D(boolean AND)A(1) systems, 9a,b, (k(ET) approximate to 5.0 x 10(9) (9a), 4.7 X 10(9) s(-1) (9b)), provide an estimate for k(ET) for the direct through space D*-> A(2) Process (Le., k(ET)(D(boolean AND)A(1)-A(2)) - k(ET)(D(boolean AND)A(1)) = k(ET)(D*-> A(2)) similar to 1 x 10(9) s(-1)). This channel of relaxation represents similar to 15% of k(ET) for D*-> A(1).