A stable organic diradicaloid with an intermolecular quintet at room temperature as a polycrystalline solid is studied. The conclusion is supported by the observation of the ΔMs = ±2 forbidden transition, electron spin resonance (ESR) simulations, and density functional theory (DFT) calculations. In addition, the molecule, as the active component of a device, is an outstanding near-infrared photodetector with detectivity over 10(11) cm Hz(1/2) W(-1) at 1200 nm.
A modular and robust method for preparing
end-functionalized donor–acceptor
(D–A) narrow bandgap conjugated polymers is reported that avoids
multistep reactions and postpolymerization modification. The strategy
is well-controlled and affords functional materials with predictable
molecular weight and high end-group fidelity. To exemplify this synthetic
strategy, narrow bandgap conjugated polymers based on PDPP2FT were
prepared that contain perylene diimide (PDI) units at the chain-ends.
Monte Carlo simulations confirm the high degree of chain-end functionalization
while photoluminescence studies reveal the unique photophysical properties
of the end-functional polymers with efficient charge transfer occurring
between the main polymer chain and PDI end-groups that results exclusively
from their covalent linkage.
We examined the effects of changing
the central bridging atom identity
from carbon (d-CDT(PTTh2)2) to silicon (d-DTS(PTTh2)2) in the cyclopentadithiophene unit in a small
molecule donor material. The substitution left the optical and electrical
properties largely unchanged but significantly modified the melting/crystallization
behavior and the formation of crystalline domains in thin film blends
with PC71BM. Solar cells made with the d-CDT(PTTh2)2:PC71BM had efficiencies less than 1%, while
thermally annealed solar cells made with d-DTS(PTTh2)2:PC71BM achieved efficiencies up to 3.4%. Morphological
analyses of the active layer film morphology were done with polarized
optical microscopy, grazing incidence wide-angle X-ray scattering,
and transmission electron microscopy and showed that large (micrometer
scale) crystals formed in the d-CDT(PTTh2)2 based
films while smaller (25 to 50 nm) crystals formed in the d-DTS(PTTh2)2, largely explaining the difference in device
performance. Thermally activated photocurrent was observed in devices
suggest that the additional current at elevated temperatures results
from thermally activated charge generation. Charge transfer excitons
were also investigated using external quantum efficiency measurements.
Sharper band tails for the small molecule donors suggest less disorder
than in P3HT:PCBM and other polymer systems.
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