Isomeric Effect in Unidirectionally Extended Fused-Ring Electron Acceptors

We designed and synthesized two isomers
AOIC1 and AOIC2 by unidirectional
extension of the same asymmetric precursor in different directions
and separated by selectivity of Lewis-acid-mediated Friedel–Crafts
reaction due to different steric hindrance of the side chains. AOIC1
and AOIC2 were compared with our reported AOIC to study the isomeric
effect. The only difference in three isomers is isomeric fused-ring
cores. The AOIC series exhibit different molecular stacking in single
crystals and dipole moments. From AOIC to AOIC1 and AOIC2, hypsochromic
optical absorption, similar lowest unoccupied molecular orbital, down-shifted
highest occupied molecular orbital, and decreased electron mobility
are presented. Organic photovoltaic cells were constructed using the
AOIC series as acceptors and wide-bandgap J71, medium-bandgap PM6,
and narrow-bandgap PTB7-Th as donors. Combinations of AOIC and PTB7-Th
with relatively narrower bandgaps as well as of AOIC1/AOIC2 and J71/PM6
with relatively broader bandgaps yielded higher device efficiencies.