Harnessing Direct (Hetero)Arylation in Pursuit of a Saddle-Shaped Perylene Diimide Tetramer

This contribution explores the direct (hetero)­arylation (DHA) cross-coupling of a saddle-like, π-conjugated cyclooctatetrathiophene (Th₄) core with the N-annulated perylene diimide (PDI) chromophore. Replacing the bulky pivalic acid with acetic acid enabled a facile cross-coupling, selectively forming a PDI tetramer (Th₄PDI₄) in a 70% overall yield. The optoelectronic properties of Th₄PDI₄ were characterized and density functional theory (DFT) was used to calculate the optimized molecular geometry and molecular orbitals (MOs). Energy levels of MOs determined by cyclic voltammetry corresponded well with those calculated using DFT. The molecular geometry calculated by DFT showed Th₄PDI₄ adopts two separate PDI–PDI conformations (propeller and double-decker). Organic photovoltaic (OPV) devices were fabricated using a blend of PTB7-Th/Th₄PDI₄, where an initial power conversion efficiency (PCE) of 1.89% was improved by testing a series of solvent additives and thermal annealing techniques. Through use of 3% (v/v) 1-chloronaphthalene additive, a combination of higher short circuit current (J_sc = 10.2 mA/cm²) and fill factor (FF = 42%) led to an overall increase in PCE to 4.26%.