Six
different boron subphthalocyanines with fluorophenoxy axial
substituents were synthesized to explore and fine-tune the HOMO and
LUMO energy levels based on past observations of the unique levels
of pentafluorophenoxy-boron subphthalocyanine (F5BsubPc).
Electrochemistry reduction potentials, ionization energies from ultraviolet
photoelectron spectroscopy (UPS) measurements, and energy levels calculated
using semiempirical methods reveal finely variable values between
phenoxy-BsubPc (PhO-BsubPc), without any fluorine atoms, and F5BsubPc, with all five fluorines. There is no trend between
the number of fluorines on the phenoxy group and the electronic properties,
but there is an influence of meta fluorine(s) altering the redox potentials
and ionization energy, leading us to categorize the fluorophenoxy-BsubPcs into two “buckets”:
with and without meta fluorines. We then applied the fluorophenoxy-BsubPcs
as electron acceptors in planar heterojunction organic photovoltaic
devices. The categorization of these “buckets” was confirmed
by the fine change in open-circuit voltage between 1.15 and 1.21 V,
which is an exceptionally high value. This level of fine-tuning of
properties and device metrics is a unique handle enabled by the phenoxy
axial substituent of BsubPcs.