Abstract
Dendrimers made of oligo(phenylene ethynylene) building blocks are highly-organised two-dimensional macromolecules that have raised much interest for their potential use as artificial light-harvesting antennae. Excitation-energy transfer is assumed to occur from the periphery to the core via a tree-shaped graph connecting a pair of donors on each acceptor. The received photophysical mechanism involves a converging cascade of crossings among bright electronic states foremost mediated by rigid acetylenic stretching modes. On the other hand, competition with in-plane transbending motions has been detected experimentally in oligomers and confirmed by computations in larger species, thus suggesting the additional involvement of dark electronic states acting as intermediates. In the present work, we show that this secondary process represents an alternative pathway that may not be detrimental and could even be viewed as a mechanistic shortcut.