Modeling Singlet Fission in Rylene and Diketopyrrolopyrrole Derivatives: The Role of the Charge Transfer State in Superexchange and Excimer Formation

• Published in: Journal of physical chemistry. C 2017-05, Vol.121 (19), p.10345-10350
• Main Authors: Miller, Claire E, Wasielewski, Michael R, Schatz, George C
• Format: Article
• Language: English
• Subjects: catalysis (homogeneous), catalysis (heterogeneous), solar (photovoltaic), solar (fuels), photosynthesis (natural and artificial), bio-inspired, hydrogen and fuel cells, electrodes - solar, defects, charge transport, spin dynamics, membrane, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly)
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.7b02697

Singlet fission (SF) is being explored as a way to improve the efficiency of organic photovoltaics beyond the Shockley-Queisser limit; however, many aspects of the SF mechanism remain unresolved. The generally accepted mechanisms provide simplified models of SF that equivocate over whether a charge transfer (CT) state is involved in SF. A one-step superexchange model allows the CT state to act as a virtual state, reducing the effect of large Gibbs free energy values from SF rate calculations. Also, extending superexchange to an excimer-mediated process allows for further refinement of the triplet formation model. Application of the superexchange and excimer-mediated models to a variety of rylene and diketopyrrolopyrrole derivatives provides new insights into the role of the CT and excimer states, providing a semiquantitative description of SF that is dictated by the CT state energy.