The Effect of Aggregation Behavior on the Photophysical Properties of Perylene Diimide Dye Derivatives as Electron Acceptors for Organic Photovoltaics.

摘要

Perylene-3,4:9,10-bis(dicarboximide) (PDI) dye derivatives with variable pi-pi stacking motifs are synthesized and studied as potential electron acceptor materials for organic photovoltaic (OPV) devices.;Two general schemes are utilized to tune the pi-pi aggregation of the PDI cores. The first involves surrounding the small molecule core with large aromatic substituents. Appending bulky aromatic substituents to the 1,7-"bay" positions serves to impede pi-pi interactions between adjacent molecules. These resultant PDI derivatives are more amenable to film fabrication via solution techniques than unsubstituted, and are thus studied in solution processed blend films with donor materials, akin to the active layer of a bulk-heterojunction (BHJ) OPV. When blended with a small molecule donor (6,13-bis(triisopropylsilyl-ethynyl)-pentacene), ultrafast charge separation is again observed, but in this case results in geminate-pair recombination to the triplet state. Furthermore, while the small molecule donor on its own undergoes singlet fission, the process is inhibited when blended with sterically-encumbered PDI.;The first scheme was then expanded to phenyl substitution at the 2,5,8,11 "headland" positions of the core. Film studies suggest J-aggregation of this derivative, and these observations were confirmed by single crystal analysis. Films of these J-aggregates demonstrate ultrafast conversion to PDI triplet via transient absorption experiments. This derivative may lead to design strategies for developing PDI derivatives for singlet fission.;The second general scheme focuses on mulitchromophore systems with the goal of taking advantage of PDI aggregation to create an intermolecular network for omnidirectional exciton transport. A tetrahedral PDI derivative was synthesized and found to undergo excitation energy transfer within the monomer. Furthermore, this molecule forms intermolecular aggregates, with long-lived excited states indicative of excimer formation.;Thus it is shown that, by varying the pi-pi stacking of PDIs in the solid state, subsequent effects can be seen in processes such as excitation energy lifetime, charge separation, singlet fission, and energy migration. Understanding of these effects can aid in design of PDI acceptors for use in OPVs.