- Yushchenko, O.; Villamaina, D.; Sakai, N.; Matile, S.; Vauthey, E. “Comparison of Charge-Transfer Dynamics of Naphthalenediimide Triads in Solution and π-Stack Architectures on Solid Surfaces” J. Phys. Chem. C 2015, 119, 14999-15008
The femto- to microsecond excited-state dynamics of an electron donor-acceptor-donor triad, consisting of two red core-substituted naphthalenediimides (rNDI) and one colourless naphthalenediimide (pNDI), in solution has been compared to that of a supramolecular surface architecture, constituted of co-axial stacks of rNDI and pNDI and prepared by self-organising surface initiated polymerisation (SOSIP). In the triad, charge separation between an excited rNDI and pNDI takes place in highly polar solvents only and for a sub-ensemble of molecules, around 30%, with a folded conformation. Other processes, such as singlet and triplet excitation energy transfer from pNDI to rNDI and intersystem crossing, are also operative. Additionally, bimolecular symmetry-breaking charge separation upon triplet-triplet annihilation is observed on the microsecond timescale in polar solvent. In the surface architecture, excitation of an rNDI is followed by an ultrafast symmetry breaking-charge separation resulting in a charge-transfer exciton, that either recombines or dissociates into a charge-separated state with the electron and the hole in different stacks. The same charge-separated state can also be populated upon excitation of pNDI, either via a charge-transfer pNDI exciton or after excitation energy transfer to rNDI. Charge recombination in the SOSIP film takes place on a wide range of timescales, ranging from a few picoseconds to several hundreds of microseconds.