Macrocyclic dyads based on C₆₀ and perylenediimides connected by click chemistry

Two sets of perylenediimide-[60]fullerene dyads PDI-C₆₀ connected through 1,2,3-triazole units have been synthesized and characterized. The cyclic dyad PDICl₄-C₆₀ has four chlorine atoms in the 1,6,7,12-PDI positions, whereas the cyclic dyad PDIPip₂-C₆₀ has two piperidine units in the 1,7-PDI positions. On the other hand, PDICl₄-C₆₀ and PDIPip₂-C₆₀ dyads were synthesized as linear counterparts with the same substitution pattern. Also, a C₆₀-PDICl₄-C₆₀ triad has been prepared. A small interaction between C₆₀ and PDI moieties in the ground state was detected by UV/vis and electrochemical measurements in both PDI-C₆₀ cyclic systems. The occurrence of photoinduced energy-transfer processes between PDI and C₆₀ units was confirmed by time-resolved emission and transient absorption techniques. Femtosecond laser flash photolysis showed energy transfer from ¹PDI* to C₆₀ followed by intersystem crossing from ¹C₆₀* to ³C₆₀* in the case of the PDICl₄-C₆₀ systems. The energy transfer rate for PDICl₄-C₆₀ in the cyclic dyad and the triad is one order of magnitude faster than that in PDICl₄-C₆₀ in the linear dyad. The fast energy transfer rate together with the enhanced molar absorption coefficient by perylenediimide functionalization will be highly beneficial for applications as acceptors in polymer solar cells. On the other hand, no electron transfer from the donor PDIpip₂ units to the acceptor C₆₀ moiety was detected in the case of PDIPip₂-C₆₀ dyads.