Long Range Coherent Energy Transfer in Artificial Multichromophoric Antenna Systems-A Case of Breaking Kasha's Rule.

Ultrafast long-range energy transfer with unitary quantum-yield has been studied in a novel family of artificial DNA-guided multichromophoric antenna complexes with phenanthrene moieties as light harvesters. By means of femtosecond transient absorption spectroscopy and time-dependent density function theory calculations, we demonstrate that the highly efficient long-range energy transfer occurs via a coherent mechanism. It is enabled by photoexcitation of higher lying delocalized excited states of phenanthrene, and hence, can be labelled anti-Kasha in nature. Moreover, we show the important contribution of exciplex formation between acceptor and closest donor.