Communication
Organic & Biomolecular Chemistry
Table 3 Photoluminescent properties of (hetero)aryl[c]- and -[a]carbazolesa
(H)A[c]Cb
λmax/nmc
3a
3d
383, 400
3j
3k
366, 384,
402sh
0.358
362, 380,
399sh
0.334
366, 383,
401sh
0.343
d
ΦF
0.298
(H)A[a]Ce
λmax/nmc
5a
360, 378,
397
0.165
5d
5j
5k
369, 388,
407
0.167
363, 378,
395sh
0.109
370, 388,
407sh
0.156
d
ΦF
(H)A[c]Cb
λmax/nmc
3f
3h
3i
3m
370, 385
374, 392,
413sh
0.391
369, 387,
405sh
0.416
372, 388,
408sh
0.481
d
ΦF
0.314
(H)A[a]Ce
λmax/nmc
5f
5h
5i
5m
371, 389,
408sh
0.184
366, 384,
403sh
0.239
367, 385,
404sh
0.264
391, 410,
431sh
0.114
d
ΦF
a Fluorescence spectra excited at 265 nm were measured in CH2Cl2 (c = 1.5 × 10−6 M). Photoluminescent data of [a]-types collected herein were
derived from ref. 3b. b (H)A[c]C = (hetero)aryl[c]carbazole. c sh = shoulder. d Determined with reference to the quantum yield of p-terphenyl. e (H)A
[a]C = (hetero)aryl[a]carbazole.
to enhancing quantum efficiency in comparison to basic struc-
ture 3a, as observed in the [a]-types (5a vs. 5f, 5h or 5i). Inter-
estingly, the quantum yields of each [c]-type were found to be
always higher than those of the corresponding [a]-type. These
structure–property correlations for AHACs might be a useful
guide to create optoelectronic devices.
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In closing, we have developed a new synthetic method for
(hetero)aryl[c]carbazoles, which can be efficiently constructed
by the two carbon–carbon bond-forming cascade in one batch
through the annulation of 3-(hetero)arylindoles with propargyl
ethers. One important aspect is the selective synthesis of 3 and
4 by the appropriate choice of the C3 source. The development
of this reaction gave us a great opportunity to evaluate emis-
sion properties of the product, thereby showing that the [c]-
type is more emissive than the [a]-type. As the finale of this
research project, the application of this strategy to the [b]-type
that remains unaddressed would be suitable. We believe that
elucidation of structure–property correlations reflecting all
three types of AHACs would be worthy of future research.
This work was supported by KAKENHI (No. 16750075), and
Izumi Science and Technology Foundation. Y.N. thanks the
JSPS Research Fellowship for Young Scientists. We appreciate
Dr Ken-ichi Fujita and Prof. Dr Hiroyuki Yasuda at AIST,
Japan, for their helpful support in HRMS measurements.
2 For selected recent articles and reviews, see: (a) Y. Ooyama
and Y. Harima, Eur. J. Org. Chem., 2009, 2903;
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4 For Jiao’s method capable of providing twenty-three [a]-
types and one [c]-type on (hetero)aryl-annulated carbazoles,
see: Z. Shi, S. Ding, Y. Cui and N. Jiao, Angew. Chem., Int.
Ed., 2009, 48, 7895.
Notes and references
1 For selected recent reviews, see: (a) H.-J. Knölker and
K. R. Reddy, Chem. Rev., 2002, 102, 4303; (b) M. Prudhomme,
1458 | Org. Biomol. Chem., 2013, 11, 1456–1459
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