Journal of the American Chemical Society
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decomposition at elevated temperatures and in light. In the
can be tuned by both the attachment point and the length of
the linker by changing the bonding thermodynamic parameꢀ
ters. Incorporation of these diradical building blocks into
solidꢀstate materials are currently being explored.
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case of the more electron donating compounds (4-6O-DMA
and 5O-JUL), EPR experiments were performed by lowerꢀ
ing the temperature to as low as 188 K and then slowly raisꢀ
ing the temperature up to 278 K to calculate thermodynamic
parameters.
ASSOCIATED CONTENT
Supporting Information
For each sample studied, toluene or dichloromethane was
added to the solid sample to make a 1ꢀ5 mM solution of radꢀ
ical/dimer species. This solution was then purged and cannuꢀ
lated into a preꢀpurged quartz EPR tube. EPR studies were
then performed at 10 degrees increments (298ꢀ378 K for
toluene and 208ꢀ298 K for dichloromethane) with an equiliꢀ
bration time of 5 minutes for each temperature increment.
The following instrument parameters were generally folꢀ
lowed for each sample: modulation frequency, 100 kHz;
receiver gain, 50 dB; modulation amplitude, 0.5; time conꢀ
stant, 0.01 s; center field, 3330 G; sweep width, ~200 G;
microwave attenuation, 20 dB; microwave power, 2 mW;
number of data points, 2048; average number of scans, 15.
All synthetic procedures, compound characterization data, van
‘T Hoff plots, Cartesian coordinates, absolute energies, and
crystal structure files. The Supporting Information is available
free of charge on the ACS Publications website.’
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AUTHOR INFORMATION
Corresponding Author
*
Ames IA, 50010
Author Contributions
Rui Zhang and Joshua P. Peterson contributed equally.
UV-Vis spectrum for 50-JUL. A 50 µM solution of 5O-JUL
in toluene was carefully prepared to avoid any light, air, or
other contamination to detect the presence of a pimer band
growing in the near IR region as the temperature was lowꢀ
ered to 233 K. Low temperature spectra were made possible
by a liquid nitrogen cooler with a nitrogen blow off to avoid
condensation on the quartz cell walls.
Funding Sources
We thank the NSF CHE 1764235 and XSEDE CHE170051 for
support of this work.
ACKNOWLEDGMENT
The authors thank Dr. Sarah Cady and the ISU chemical instruꢀ
ment facility for assistance with variable temperature EPR acꢀ
quisition.
Computational methods. All computations were carried out
[
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in Gaussian16.
Nonꢀtethered dimers and radicals for the
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