In by admin

NameMr. Parag Das
Organization or InstitutionUniversity of Florida
TopicOrganic Chemistry
Title

The photoisomerization behavior of INCN-functionalized donor-acceptor molecules

Author(s)

Parag Das, Cory T. Kornman, Ion Ghiviriga, Khalil A. Abboud, and Ronald K. Castellano*

Author Institution(s)

University of Florida

Abstract

2-(3-Oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) is a popular electron deficient unit introduced to small molecule (SM) non-fullerene acceptor (NFA) materials used in bulk-heterojunction organic photovoltaics (OPVs). Since its introduction in 2015, the INCN unit has been showcased in hundreds of push-pull oligomers and has served an important role in the development and understanding of small molecule-based OPVs. Interestingly, the configuration and conformation of the exocyclic olefin which conjugates INCN to pi-conjugated materials has been largely overlooked. It is anticipated based on our prior work that the stereochemistry of the double bond can significantly affect the electronic properties and solid-state morphology of thin films of such small oligomeric molecules. To begin testing this hypothesis, we have designed and synthesized a library of small molecules functionalized with INCN that vary in donor unit, conjugation length, steric crowding, and end-group substitution to modulate the electronic character and conformational preferences. The molecules all undergo well-controlled Z/E photoisomerization using different selective irradiation sources, yielding a range of Z/E photostationary state (PSS) distributions. The isomerization behavior at nearly all wavelengths is well-behaved, and facile photoswitching has been demonstrated over ten cycles for several model compounds. Complementary DFT calculations will also be discussed that provide additional mechanistic insight on the photochemical behavior of INCN-functionalized molecules. The results clarify about two recent literature reports of photoisomerization related photodegradation of INCN-functionalized donor-acceptor molecules using broad spectrum irradiation sources.