| Abstract
| - The branched donor−acceptor triad 4 and tetrad 5 were synthesized to study the possibility of controlling thedirection of electron transfer in a divergent array of electron acceptors using ultrafast laser pulses. Compounds4 and 5 employ 1,3,5-triaminobenzene as the central branch point. In 4, a 4-(N-piperidinyl)-1,8-naphthaleneimideelectron donor (ANI) was attached to the 1 position and two electron acceptors, 1,8:4,5-naphthalenediimide,NI, and pyromellitimide, PI, were attached to the 3 and 5 positions of the central benzene ring. In 5, theterminal end of the PI acceptor is functionalized with an additional NI molecule. Selective excitation of ANIin 4 and 5 with 400 nm, 130 fs laser pulses results in exclusive formation of NI-−ANI+−PI and NI-−ANI+−PI−NI, respectively, with τ = 115 ps, and a quantum yield of 0.99. Excitation of NI- with 480 nm,130 fs laser pulses produces the excited doublet state *NI-, which transfers an electron to PI on the secondbranch of the benzene ring with a time constant of τ = 600 fs in 4 and τ = 750 fs in 5. The overall quantumyields for the two step process are 0.44 and 0.36 in 4 and 5, respectively. The resultant state NI−ANI+−PI-in 4 undergoes a charge shift reaction returning to the initial ion pair state NI-−ANI+−PI with τ = 400 ps,while the corresponding state NI−ANI+−PI-−NI in 5 undergoes a charge shift with τ = 200 ps to yieldNI−ANI+−PI−NI-, which in turn exhibits a 2000 ps lifetime. These results show that once the electron hasbeen switched to the branch containing the thermodynamically uphill PI acceptor, the electron will cascadedown that branch to other acceptors that are more easily reduced. Model compounds 1−3, which weresynthesized to aid in characterization of the switching dynamics, are also discussed. Photochemical controlof directional charge transport may make it possible to design networks of organic molecules for informationprocessing.
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