Efficient singlet fission in nanoparticles of amphipathic anthracene-tetracene dyad with broadband light harvesting ability

Efficient singlet fission (SF) materials with relatively high triplet state energy and broadband light harvesting ability simultaneously have a greater advantage for practical application in photovoltaics. Herein, we prepared colloid nanoparticles of an amphipathic anthracene (DPA)-tetracene (DPT) dyad (DPT-DPA-COOH) with broadband light harvesting. The DPA unit compensates the weak absorption of the DPT unit at shorter than 425 nm wavelength via ultrafast (< 1 ps) and quantitative intramolecular singlet Forster resonance energy transfer (FRET) from the DPA unit to the DPT unit. Transient absorption spectroscopy demonstrated that a fast (similar to 73 ps) and efficient (phi<INF>T<INF>1</INF></INF> = similar to 110%) intermolecular SF (xSF) between the adjacent DPT units of the DPT-DPA-COOH molecule in nanoparticles could be initiated by the near-unity intramolecular FRET. The close arrangement between the DPT units enforced by the extra hydrophilic interaction induced by the carboxyl group is the key for achieving efficient xSF. These results suggest that the link of proper singlet energy donor (antennas) to the SF chromophore via covalent bond is a good option for designing xSF materials with broadband light harvesting ability.