2 research outputs found
Steric Control of Luminescence in Phenyl-Substituted Trityl Radicals
Triphenylmethyl (trityl) radicals have shown potential
for use
in organic optoelectronic applications, but the design of practical
trityl structures has been limited to donor/radical charge-transfer
systems due to the poor luminescence of alternant symmetry hydrocarbons.
Here, we circumvent the symmetry-forbidden transition of alternant
hydrocarbons via excited-state symmetry breaking in a series of phenyl-substituted
tris(2,4,6-trichlorophenyl)methyl (TTM) radicals. We show that 3-fold
phenyl substitution enhances the emission of the TTM radical and that
steric control modulates the optical properties in these systems.
Simple ortho-methylphenyl substitution boosts the
photoluminescence quantum efficiency from 1% (for TTM) to 65% at a
peak wavelength of 612 nm (for 2-T3TTM) in solution. In
the crystalline solid state, the neat 2-T3TTM radical shows
a remarkably high photoluminescence quantum efficiency of 25% for
emission peaking at 706 nm. This has implications in the design of
aryl-substituted radical structures where the electronic coupling
of the substituents influences variables such as emission, charge
transfer, and spin interaction
Tailoring Interlayer Charge Transfer Dynamics in 2D Perovskites with Electroactive Spacer Molecules
The family of hybrid organic–inorganic lead-halide
perovskites
are the subject of intense interest for optoelectronic applications,
from light-emitting diodes to photovoltaics to X-ray detectors. Due
to the inert nature of most organic molecules, the inorganic sublattice
generally dominates the electronic structure and therefore the optoelectronic
properties of perovskites. Here, we use optically and electronically
active carbazole-based Cz-Ci molecules,
where Ci indicates an alkylammonium chain
and i indicates the number of CH2 units
in the chain, varying from 3 to 5, as cations in the two-dimensional
(2D) perovskite structure. By investigating the photophysics and charge
transport characteristics of (Cz-Ci)2PbI4, we demonstrate a tunable electronic coupling
between the inorganic lead-halide and organic layers. The strongest
interlayer electronic coupling was found for (Cz-C3)2PbI4, where photothermal deflection spectroscopy
results remarkably reveal an organic–inorganic charge transfer
state. Ultrafast transient absorption spectroscopy measurements demonstrate
ultrafast hole transfer from the photoexcited lead-halide layer to
the Cz-Ci molecules, the efficiency of
which increases by varying the chain length from i = 5 to i = 3. The charge transfer results in long-lived
carriers (10–100 ns) and quenched emission, in stark contrast
to the fast (sub-ns) and efficient radiative decay of bound excitons
in the more conventional 2D perovskite (PEA)2PbI4, in which phenylethylammonium (PEA) acts as an inert spacer. Electrical
charge transport measurements further support enhanced interlayer
coupling, showing increased out-of-plane carrier mobility from i = 5 to i = 3. This study paves the way
for the rational design of 2D perovskites with combined inorganic–organic
electronic properties through the wide range of functionalities available
in the world of organics