Table 1. Optical properties of 9-arsafluorenes (3a, 3b)
to the 1a or 1b at room temperature, the color of iodine
disappeared a few minutes later. Especially in the case of 1a,
a homogeneous solution was obtained, even though 1a is
insoluble in common organic solvents such as diethyl ether
(Et2O), tetrahydrofuran, toluene, and CHCl3 (Figure S9). The
1H NMR analysis of the reaction mixtures after 30 min showed
disappearance of the original signals for 1a and 1b and
appearance of new signals corresponding to diiodomethylarsine
(2b)9d and diiodophenylarsine (2a), respectively.
After mixing 1a, and 1b with an equivalent amount of
iodine against the arsenic atom in Et2O at room temperature,
corresponding Et2O solutions of 2a and 2b were obtained.
The obtained solutions of 2 were added to an Et2O solution of
2,2¤-dilithiobiphenyl at 0 °C and the reaction mixtures were
allowed to warm to room temperature. After stirring the reaction
mixtures overnight, 9-phenyl-9-arsafluorene (3a) and 9-methyl-
9-arsafluorene (3b) were obtained in 89% and 47% yields,
respectively (Scheme 2).12 To compare with an organophos-
phorus analog, 9-phenyl-9-phosphafluorene (4) was prepared
following a reported procedure.2d
a
b
d
-
-
-
abs
ex
em
c
ΦPL
/nm
/nm
/nm
3a
3b
324
321
387, 515
370, 500
0.31
0.33
281
279
aExcitation maxima determined by 510 nm emission at 77 K.
bLocal emission maxima excited at 322 nm at 77 K. cQuantum
yields in solid state under 322 nm irradiation for excitation at
d
77 K. UV-vis absorption maxima in CHCl3 at r.t.
enhanced with decreasing temperature and the emission band of
phosphorescence is of lower energy than that of fluorescence.
Compared with 4, the organoarsenic analogues 3a showed
relatively prominent phosphorescence (Figure 2) and the quan-
tum yield of 4 (Φ = 0.09) is less than that of 3a (Φ = 0.31)
(Table 1), which suggests efficient intersystem crossing by
heavy-atom effect of the arsenic atom. The emission maxima of
3a were red-shifted compared with those of 3b, suggesting a
lower energy photoexcitation process for 3a. This observation
was correlated to the UV-vis adsorption maxima i.e., the UV-
vis adsorption maximum of 3a was slightly red-shifted com-
pared with that of 3b.
In summary, we have developed a novel and facile As-C
bond formation method. The key step of this method is the
in-situ generation of arsenic diiodides from organoarsenic
homocycles and iodine. We applied this method for preparing
9-arsafluorenes and studied their optical properties. The 9-
arsafluorenes showed intense solid-state PL at 77 K and
excellent air-stability. 9-Arsafluorenes are promising superior
candidates for optoelectrical materials due to inherent properties
derived from the arsenic atom. Detailed studies for emission
properties, coordination behavior and polymerization for poly-
arsafluorenes are currently in progress in our laboratory.
Air-stability was studied by bubbling air through CHCl3
solutions of 3a, 3b, and 4 for 8 h at room temperature. Although
8 mol % of 4 was oxidized to 9-phenyl-9-phosphafluorene oxide
1
according to H NMR analysis, no oxidation for 3a and 3b was
observed (Figures S5 and S6). Superior air stability of 3 to
that of 4 is expected to be a factor in using 3a and 3b as
optoelectrical materials.
No room-temperature photoluminescence (PL) was ob-
served for 3a in solutions. This observation is in agreement with
the previous reports, i.e., quantum yields of PL for 3a8c and
a phenyl-substituted arsole13 were quit low compared with a
phosphorus analogue in solution, due to increased quenching
efficiency of the heavier atom. However, we found for the first
time that 3a displayed solid-state PL (-max = 390 nm, Φ = 0.03)
at room temperature; at 77 K, in addition to the 387 nm peak, an
intense peak at -max = 515 nm was observed (Figure S8). Solid-
state PL spectrum of 3b at 77 K also showed two emission
maxima similar to that of 3a (Figure 2), but neither solution-
state nor solid-sate PL was observed for 3b at room temperature.
The emission bands at around 500 nm are probably attributed to
phosphorescence, while those at around 400 nm are attributed
to fluorescence, because phosphorescence is expected to be
This study is a part of a Grant-in-Aid for Scientific Research
on Innovative Areas “New Polymeric Materials Based on
Element-Blocks (No. 2401)” (No. 24102003) of The Ministry
of Education, Culture, Sports, Science and Technology, Japan.
Supporting Information is available electronically on J-STAGE.
References and Notes
1
44. b) K. Geramita, J. McBee, Y. Tao, R. A. Segalman, T. D.
e) S. Zhang, R. Chen, J. Yin, F. Liu, H. Jiang, N. Shi, Z. An,
2
Leenders, C. R. A. Hommersom, F. P. J. T. Rutjes, F. L.
Figure 2. Solid-state PL spectra of 3a (blue), 3b (green)
(-ex = 322 nm), and 4 (light blue) (-ex = 342 nm) at 77 K.
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