129.56, 128.72, 128.68, 128.32, 128.11, 127.77, 127.75, 127.67,
127.55, 127.01, 126.06, 125.77 and 110.77.
Photoinduced cross radical coupling was monitored by
1H NMR spectroscopy of an equimolar mixture of 1-1
and 2-2, 1-2 or 2-1 as the starting material (6.7 mM in CDCl3).
The solution was de-gassed by a freeze–pump–thaw cycle,
allowed to dissociate into two imidazolyl radicals by irradiating
it with visible light (400–700 nm, 16.6 mW cmꢂ2) and
recombined into HABIs. After terminating the photoirradiation,
the reaction solution was cooled for 10 min at room temperature
and its 1H NMR spectrum measured. This protocol was
repeated until a photostationary state was reached.
1-2 was recrystallized from dichloromethane/ethanol to
give yellow needles. 1H NMR (500 MHz, CDCl3): d = 7.71
(d, J = 7.6 Hz, 1H), 7.63–7.56 (m, 3H), 7.41–7.35 (m, 3H),
7.26–7.06 (m, 12H), 6.95–6.87 (m, 3H) and 6.59 (d, J = 2.4 Hz,
1H). 13C NMR (125 MHz, CDCl3): d = 168.98, 166.89, 144.11,
138.44, 137.95, 134.82, 134.55, 134.50, 134.25, 132.55, 131.66,
131.57, 131.52, 131.41, 131.34, 130.27, 130.18, 129.86, 129.67,
129.59, 128.90, 128.84, 128.47, 128.41, 127.84, 127.78, 127.02,
127.00, 126.29, 126.11 and 110.05.
This work was supported by a Grant-in-Aid for Science
Research in the Priority Area ‘‘New Frontiers in Photochromism’’
(471) (no. 19050011) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
2-1 was recrystallized from dichloromethane/acetonitrile to
give yellow blocks. 1H NMR (500 MHz, CDCl3): d = 7.66 (d,
J = 2.4 Hz, 1H), 7.62 (d, J = 8.0 Hz, 2H), 7.57 (t, J = 7.6 Hz,
1H), 7.48–7.39 (m, 6H), 7.26–7.21 (m, 6H), 7.14–7.06 (m, 6H),
7.00–6.97 (m, 1H), 6.92 (d, J = 2.4 Hz, 1H), 6.69 (dd, J = 8.0
and 1.6 Hz, 1H) and 6.55–6.52 (m, 1H). 13C NMR (125 MHz,
CDCl3): d = 168.38, 166.15, 142.12, 137.72, 134.21, 134.12,
132.89, 131.95, 131.84, 131.68, 131.30, 131.28, 130.91, 130.87,
130.11, 130.03, 129.94, 129.56, 129.43, 128.80, 128.47, 128.40,
128.03, 127.89, 127.87, 127.70, 126.92, 126.31, 125.87 and
110.52.
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1342 | New J. Chem., 2009, 33, 1339–1342