Excitonic Funneling in Extended Dendrimers with Non-Linear and Random   Potentials
  The mean first passage time (MFPT) for photoexcitations diffusion in a funneling potential of artificial tree-like light-harvesting antennae (phenylacetylene dendrimers with generation-dependent segment lengths) is computed. Effects of the non-linearity of the realistic funneling potential and slow random solvent fluctuations considerably slow down the center-bound diffusion beyond a temperature-dependent optimal size. Diffusion on a disordered Cayley tree with a linear potential is investigated analytically. At low temperatures we predict a phase in which the MFPT is dominated by a few paths. 
Subhadip Raychaudhuri, Yonathan Shapir, Vladimir Chernyak, and Shaul   Mukamel