Activating intramolecular singlet exciton fission by altering π-bridge flexibility in perylene diimide trimers for organic solar cells
Benedetta Carlotti, Ifeanyi K. Madu, Hyungjun Kim, Zhengxu Cai, Hanjie Jiang, Angelar K. Muthike, Luping Yu, Paul M. Zimmerman, Theodore Goodson
Abstract
conventional intersystem crossing. However, clear evidence of efficient and fast intramolecular singlet exciton fission (iSEF) is observed in the twisted trimer compound with weaker ICT character. Multiexciton triplet generation and separation occur in the twisted (flexible-bridged) PDI trimer, where weak coupling among the units is observed as a result of the degenerate double triplet and quintet states, obtained by quantum chemical calculations. The high triplet yield and fast iSEF observed in the twisted compound are due not only to enthalpic viability but also to the significant entropic gain allowed by its trimeric structure. Our results represent a significant step forward in structure-property understanding, and may direct the design of new efficient iSEF materials.