posted on 2019-03-13, 00:00authored byRen A. Wiscons, Veaceslav Coropceanu, Adam J. Matzger
Charge-transfer (CT) cocrystals formed
between π-electron
donor and acceptor molecules present diverse electronic behavior that
can be rapidly modified due to the exchangeable nature of the CT partners.
Unfortunately, chemical modifications to the donor and/or acceptor
molecules often result in altered crystal packing that yields unpredictable
changes in charge transfer and electronic coupling. Formation of solid
solutions between isomorphous CT cocrystals offers an approach to
predictably tune the electronic performance of CT materials because
the packing motif is unaffected by compositional changes. We have
formed ternary and quaternary CT solid solutions containing 4,6-dimethyldibenzothiophene
(DMDBT), 4,6-dimethyldibenzoselenophene (DMDBS), 2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ), and 2,3-dibromo-5,6-dicyanobenzoquinone (DBQ) and have mapped
the composition-dependent stability field for these materials using
a combination of single-crystal X-ray diffraction, energy dispersive
X-ray spectroscopy, and Raman spectroscopy. The CT solid solutions
show tunable degrees of charge transfer (ρ), ranging from 0.005
to 0.19 e, and optical band gaps (Eopt) between 1.26(1) and 1.38(1) eV that are dependent on the DDQ:DBQ
molar ratio. Additionally, we have exploited the isostructurality
of the DMDBT–DDQ and DMDBT–DBQ cocrystal phases to produce
single crystals with core–shell structures, demonstrating that
methods adopted to optimize and passivate inorganic electronic materials
can also be implemented for organics.