Aggregation-induced emission and thermally activated delayed fluorescence of 2,6-diaminobenzophenones

Article abstract of DOI:10.1007/s11426-018-9301-6

Exploration of novel organic luminophores that exhibit thermally activated delayed fluorescence (TADF) in the aggregated state is very crucial for advance of delayed luminescence-based applications such as time-gated bio-sensing and temperature sensing. W

Full text of DOI:10.1007/s11426-018-9301-6

SCIENCE CHINA
Chemistry
•ARTICLES• . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . https://doi.org/10.1007/s11426-018-9301-6
SPECIAL TOPIC: Aggregation-induced Emission
Aggregation-induced emission and thermally activated delayed
fluorescence of 2,6-diaminobenzophenones
Masaki Shimizu*, Masaki Nakatani & Kenta Nishimura
Faculty of Molecular Chemistry and Engineering, Kyoto Institute of Technology, Kyoto 606-8585, Japan
Received April 30, 2018; accepted June 5, 2018; published online July 13, 2018
Exploration of novel organic luminophores that exhibit thermally activated delayed fluorescence (TADF) in the aggregated state
is very crucial for advance of delayed luminescence-based applications such as time-gated bio-sensing and temperature sensing.
We report herein that synthesis, photophysical properties, molecular and crystal structures, and theoretical calculations of 2,6-bis
(diarylamino)benzophenones. Absorption spectra in solution and calculations using density functional theory (DFT) method
revealed that the optical excitation took place through intramolecular charge-transfer from one diarylamino moiety to an aroyl
group. While the benzophenones did not luminesce in solution, the solids of the benzophenones emitted green light with
moderate-to-good quantum yields. Thus, the benzophenones exhibit aggregation-induced emission. Based on the lifetime
measurement, the green emission of the solids was found to include TADF. The emergence of the TADF is supported by the small
energy gap between the excited singlet and triplet states, which was estimated by time-dependent DFT calculations. Thin films of
poly(methyl methacrylate) doped by the benzophenones also showed green prompt and delayed fluorescence whose lifetimes
were in the order of microseconds. Linear correlation between logarithm value of TADF lifetime and temperature was observed
with the benzophenone in powder, suggesting that the benzophenones can serve as molecular thermometers workable under
aqueous conditions.
donor-acceptor system, delayed fluorescence, temperature sensor
Citation:
Shimizu M, Nakatani M, Nishimura K. Aggregation-induced emission and thermally activated delayed fluorescence of 2,6-diaminobenzophenones.
Sci China Chem, 2018, 61, https://doi.org/10.1007/s11426-018-9301-6
1 Introduction
excited state (T1) by reverse intersystem crossing, a small
energy gap between S1 and T1 (∆EST) is essential for realizing
TADF. Organic luminophores including TADF-emissive
ones mostly experience severe concentration quenching of
luminescence in the aggregated state [9,10]. Hence, TADF
can be generally attained when the luminophore is dispersed
in a host matrix, whereas is difficult to observe in neat solids
[11–14]. However, efficient TADF in neat solid can allow us
to develop nondoped TADF-based OLEDs, which have
several advantages over doped OLEDs. As bio-imaging and
-sensing are usually carried out in aqueous conditions where
organic luminophores readily form aggregates, the realiza-
tion of TADF in neat solid is also desired in view of such
target-detecting applications in water. Several organic lu-
Organic luminophores that exhibit thermally activated de-
layed fluorescence (TADF) have drawn attention as emitters
for organic light-emitting diodes (OLEDs) because internal
quantum efficiency for TADF emitter-based OLEDs can, in
principle, reach to 100% [1–4]. The long-lived luminescence
is also beneficial for applications to time-gated bio-imaging
and chemical sensing, which can eliminate the effects of
background emission and scattered excitation light [5–8].
Since TADF is a radiative decay process from the lowest
singlet excited state (S1) generated from the lowest triplet
*Corresponding author (email: mshimizu@kit.ac.jp)
© Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2018 . . . . . . . . . . . . . . . . . . . . . chem.scichina.com link.springer.com

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minophores that exhibit aggregation-induced emission (AIE)
of TADF are developed, but the repertoire of the molecular
structures is quite limited [15–23]. Therefore, it is important
to explore a novel class of AIE-active TADF emitters and
disclose their photophysical properties.
ganic layer was washed with water, dried over anhydrous
MgSO4, and concentrated in vacuo. The crude product,
KMnO4 (1.4 g, 8.8 mmol), t-BuOH (30 mL), and water
(30 mL) were charged into a 300 mL three-necked flask, and
the mixture was stirred at 60 °C for 12 h. The resulting
mixture was filtered through a pad of Celite, and the filtrate
was extracted with EtOAc (50 mL). The combined organic
layer was washed with water (three times), dried over an-
hydrous MgSO4, and concentrated in vacuo. The crude
product was purified with column chromatography on silica
gel (eluent: hexane/EtOAc, 10:1) and then recrystallization
from CH2Cl2/hexane to give 2,6-dibromobenzophenone
(2.3 g, 6.8 mmol, 68%) as colorless solid. An 80 mL Schlenk
flask was charged with 2,6-dibromobenzophenone (0.80 g,
2.3 mmol), Pd2(dba)3 (84 mg, 91 μmol, 4 mol%), 2-dicy-
During our studies on the development of donor and ac-
ceptor-substituted organic luminophores that exhibit effi-
cient solid-state emission [24–33], we found that powder of
2-(diarylamino)isophthalic acid diesters that can be classi-
fied as 1,3-bis(acceptor)-2-donor-substituted benzenes
(ADA), showed aggregation-induced fluorescence, and the
thin film of poly(methyl methacrylate) (PMMA) doped with
the diesters exhibited delayed fluorescence (Scheme 1) [34].
The emergence of delayed fluorescence with the iso-
phthalates is ascribed to the largely twisted conformation and
the intramolecular charge-transfer (ICT) from the diaryla-
mino group to the isophthalate moiety, both of which are
originated from the sandwiching layout of a donor with two
acceptors on a benzene core. Then, we became interested in
1,3-bis(donor)-2-acceptor-substituted benzenes (DAD),
which can be regarded as an electronically reversed structure
of 2-(diarylamino)isophthalic acid diester, as novel lumino-
phores exhibiting delayed fluorescence (Scheme 1). We re-
port herein the synthesis, photophysical properties,
molecular and crystal structures, and theoretical calculations
of 2,6-bis(diarylamino)benzophonones 1 as one example of
DAD-type luminophores.
clohexylphosphino-2′,4′,6′-triisopropylbiphenyl
(XPhos;
0.18 g, 0.38 mmol, 16 mol%), and K2CO3 (1.3 g, 9.2 mmol).
The flask was evacuated and filled with argon. This eva-
cuation-argon filling operation was repeated twice. To the
flask was added toluene (8 mL) and aniline (0.44 mL,
4.8 mmol). The solution was stirred at 100 °C for 21 h. The
resulting solution was diluted with EtOAc (30 mL), filtered
through a pad of Celite, and concentrated in vacuo. The
crude product was purified by silica gel column chromato-
graphy (eluent: hexane/EtOAc, 10:1) to give 2,6-bis(phe-
nylamino)benzophenone (0.70 g, 0.19 mmol, 83%) as
orange solid. To an 80 mL Schlenk flask was added 2,6-bis
(phenylamino)benzophenone (0.36 g, 1.0 mmol), K2CO3
(0.56 g, 4.0 mmol), and Cu (19 mg, 0.30 mmol, 30 mol%).
The flask was evacuated and filled with argon. This eva-
cuation-argon filling operation was repeated twice. Iodo-
benzene (5 mL) was added to the flask. The resulting mixture
was stirred at 200 °C for 3 d. The mixture was diluted with
CH2Cl2 (30 mL) and filtered through a pad of Celite, and
concentrated in vacuo. The crude product was purified by
silica gel column chromatography (eluent: hexane/EtOAc,
10:1) and then recrystallization from CH2Cl2/hexane (three
times) to give 1a (0.48 g, 0.93 mmol, 93%) as yellow-green
solid.
2 Experimental
To a 250 mL Schlenk flask charged with tetrahydrofuran
(THF) (30 mL) and 1,3-dibromobenzene (1.2 mL, 10 mmol)
was added lithium diisopropylamide (1.4 M in THF, 7.6 mL,
11 mmol) slowly at –78 °C. The solution was stirred at
–78 °C for 1 h. Benzaldehyde (1.0 mL, 10 mmol) was slowly
added to the flask at –78 °C, and the resulting mixture was
warmed to room temperature and stirred for 17 h before
quenching with sat. aq. NH4Cl (30 mL). The aqueous layer
was extracted with EtOAc (50 mL) and the combined or-
1a: Tm=124 °C, Td=286 °C. TLC: Rf=0.42 (hexane/EtOAc,
1
10:1). H NMR (CDCl3, 400 MHz): δ 6.80–6.83 (m, 12H),
7.00–7.07 (m, 10H), 7.14 (d, J=8.0 Hz, 2H), 7.19–7.24 (m,
3H), 7.38 (t, J=8.0 Hz, 1H); 13C NMR (CDCl3, 100 MHz): δ
122.3, 123.4, 125.5, 127.0, 128.7, 129.0, 130.9, 132.2, 136.4,
136.5, 147.4, 147.6, 194.0. IR (neat): 3055, 1658, 1581,
1487, 1444, 1249, 1074, 916, 748, 692 cm–1. HRMS (FAB):
[M]+ calcd for [C37H28N2O]: 516.2202, found: 516.2209.
1b: Isolated in 86% yield. Tm=136 °C, Td=294 °C. TLC:
Rf=0.36 (hexane/EtOAc 10:1). 1H NMR (CDCl3, 400 MHz):
δ 3.71 (s, 3H), 6.49 (d, J=8.4 Hz, 2H), 6.79–6.83 (m, 12H),
7.03–7.07 (m, 8H), 7.14 (d, J=8.0 Hz, 2H), 7.19 (d, J=
8.4 Hz, 2H), 7.35 (t, J=8.0 Hz, 1H); 13C NMR (CDCl3,
100 MHz): δ 55.1, 112.2, 122.1, 123.3, 125.6, 128.6, 130.0,
Scheme 1 Molecular structures of 2,6-diaminobenzophenones 1.

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130.6, 131.2, 136.8, 147.4, 162.5, 192.5. IR (neat): 3003,
1654, 1587, 1483, 1442, 1315, 1247, 1166, 1022, 923, 750,
688 cm–1. HRMS (FAB): [M]+ calcd for [C38H30N2O2]:
546.2307, found: 546.2307.
3.2 Photophysical properties
3.2.1 UV-visible absorption properties in solution
UV-visible absorption data and spectra of 1 in a 2:1:1 mixed
solution of diethyl ether, toluene, and ethanol (ETE) are
shown in Table 1 and Figure 1, respectively. The weak and
broad bands were observed with absorption maxima at
365–378 nm. The absorption maxima of 1c possessing (4-t-
BuC6H4)2N, more electron-donating group than Ph2N, and 1b
bearing 4-MeOC6H4CO, less electron-accepting group than
PhCO, were red- and blue-shifted, respectively, compared
with that of 1a. Based on the experimental results and the-
oretical calculations using density functional theory (DFT),
the weak bands were ascribed to ICT from one diarylamino
moiety to the aroyl group (see 3.4 Theoretical calculations).
The hypochromic shift of absorption maximum of 1d with
respect to 1a implied that the effective conjugation length of
1d was shorter than that of 1a. This may be reasonable by
assuming that the conformation of diarylamino groups of 1d
is more twisted than those of 1a due to the sterically de-
manding ortho-tolyl groups.
1c: Isolated in 75% yield. Tm (dec)=330 °C. TLC: Rf=0.75
1
(hexane/EtOAc, 10:1). H NMR (CDCl3, 400 MHz): δ 1.19
(s, 36H), 6.72 (d, J=8.4 Hz, 8H), 6.90 (t, J=7.6 Hz, 2H), 7.02
(d, J=8.4 Hz, 8H), 7.09–7.12 (m, 5H), 7.34 (t, J=7.6 Hz, 1H);
13C NMR (CDCl3, 100 MHz): δ 31.4, 34.0, 122.8, 125.3,
125.4, 126.7, 129.0, 130.6, 131.8, 136.3, 136.4, 144.6, 145.0,
147.8, 194.4. IR (neat): 2955, 1620, 1565, 1506, 1456, 1363,
1263, 1192, 1120, 920, 825, 688 cm–1. HRMS (FAB): [M]+
calcd for [C53H60N2O]: 740.4706, found: 740.4700.
1d: Isolated in 70% yield. Tm=149 °C, Td=303 °C. TLC:
Rf=0.62 (hexane/EtOAc, 10:1). 1H NMR (CDCl3, 400 MHz):
δ 1.39 (s, 6H), 6.74–6.84 (m, 12H), 6.96 (t, J=8.0 Hz, 2H),
7.04 (d, J=8.0 Hz, 4H), 7.09 (t, J=8.0 Hz, 4H), 7.20 (t, J=
8.0 Hz, 1H), 7.25–7.31 (m, 3H); 13C NMR (CDCl3,
100 MHz): δ 18.3, 121.3, 121.6, 123.5, 124.8, 126.5, 127.1,
127.9, 128.7, 129.0, 129.8, 131.2, 132.1, 134.4, 134.9, 135.7,
144.6, 148.2, 148.6, 193.8. IR (neat): 3016, 1664, 1568,
1485, 1446, 1226, 1114, 1033, 925, 752, 692 cm–1. HRMS
(FAB): [M]+ calcd for [C39H32N2O]: 544.2515, found:
544.2521.
3.2.2 Aggregation-induced emission
All of 1 in solution were non-luminescent at room tem-
perature. The luminescence quenching was probably as-
cribed to intramolecular motions possible in solution and
collision with solvent molecules at room temperature, which
led to the loss of the excited energy. Then, AIE behavior was
examined by adding water to a THF solution of 1b (Figure 2.
For 1a, 1c, and 1d, see Supporting information online). The
mixed solutions of THF and water were non-emissive when
3 Results and discussion
3.1 Synthesis of 2,6-diaminobenzophenones 1
Diaminobenzophenones 1 were synthesized from 1,3-di-
bromobenzene (Scheme 2). Carbonyl addition of 2,6-di-
bromophenyllithium, generated from the dibromobenzene
with LDA, to Ar1CHO gave the corresponding dia-
rylmethanols, which was oxidized with KMnO4 to afford
2,6-dibromophenyl ketones. Pd-catalyzed amination of the
dibrominated ketones with anilines Ar2NH2 and subsequent
coupling with aryl iodides Ar3-I with the aid of copper cat-
alyst provided 1 in good-to-high yields.
Table 1 Absorption data of 1 in a 2:1:1 mixed solution (10–5 M) of diethyl
ether, toluene, and ethanol (ETE)
1
λabs (nm)
373
ε (M–1 cm–1)
2200
1a
1b
1c
1d
365
3100
378
2200
365
6000
Figure 1 Absorption spectra of 1 in ETE (10–5 M) (color online).
Scheme 2 Synthesis of 1.

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Figure 3 Fluorescence spectra of 1 in the solid state at 298 K in air (color
online).
decay rates: one was in the order of nanoseconds and the
other was in the order of microseconds. Hence, 1 in the solid
state was found to exhibit dual emission of prompt and de-
layed fluorescence.
3.2.4 Photoluminescence properties in solution at 77 K
A solution of 1 in ETE at 77 K exhibited green emission at
485–509 nm with good-to-excellent quantum yields of 0.56–
0.92 (Table 3 and Figure 4). The emission maxima of 1b and
1c were hypsochromically and bathochromically shifted,
respectively, compared with 1a, which corresponded to the
trend of their absorption maxima and ICT character. The
lifetimes of long-lived emission at 77 K were in the order of
milliseconds, which were much longer than those of the
solids at 298 K, and the long-lived emission is assignable as
Figure 2 Optical (upper line) and luminescent (lower line) images and
fluorescence spectra of 1b in THF/H2O (color online).
the water fraction was less than 90%. In case that the water
fraction reached to 90%, the solution became green-lumi-
nescent. As 1b was insoluble in water, the high water content
in the mixed solution forced 1b to form aggregates in which
intramolecular motions resulting in non-radiative decay was
suppressed. Hence, 1 was confirmed to exhibit AIE [35,36].
Table 3 Photoluminescence data of 1 in ETE at 77 Ka)
1
λem (nm)
504
Φ
τ1 (ns)
2.8
τ2 (ms)
10.0
21.2
7.8
1a
1b
1c
1d
0.76
0.92
0.84
0.56
492
4.4
3.2.3 Photoluminescence properties in the solid state
As the aggregates of 1 showed luminescence, we next in-
vestigated the photoluminescence of 1 in the solid state at
298 K in air. The data and spectra are shown in Table 2 and
Figure 3, respectively. Each solid emitted green light with
emission maxima at 489–500 nm with moderate-to-good
quantum yields of 0.36–0.58. The luminescence lifetime
measurements revealed that the green emission included two
509
3.8
485
2.8
18.7
a) Excitation was affected by UV irradiation at 350 nm for 1a, 1b, and
1d, and 360 nm for 1c.
Table 2 Photoluminescence data of 1 in the solid state at 298 K in aira)
1
λem (nm)
500
Φ
τ1 (ns)
3.0
τ2 (μs)
4.4
1a
1b
1c
1d
0.58
0.55
0.41
0.36
496
3.6
3.3
498
5.4
7.9
489
0.6
1.8
a) Excitation was affected by UV irradiation at 350 nm for 1a, 1b, and
1d, and 360 nm for 1c.
Figure 4 Fluorescence spectra of 1 in ETE at 77 K (color online).

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phosphorescence. Although the quantum yields at 77 K were
much higher than those of solids at 298 K, no discernible
phosphorescence band was observed in the spectra shown in
Figure 4, suggesting that the values of ∆EST were very small.
3.3 Molecular and crystal structures of 1b
Recrystallization of 1b from hexane/CH2Cl2 solution gave its
single crystals suitable for X-ray diffraction analysis [37].
The carbonyl group is twisted with respect to the diamino-
benzene ring by 55.86° to diminish the steric repulsion
against the two NPh2 groups (Figure 6(a)). Each bond angle
around the nitrogen atoms is almost 120°, indicating that the
nitrogen atoms are sp2 hybridized. As shown in Figure 6(b), a
carbonyl moiety and one phenyl group of a Ph2N moiety
form intramolecular π-π stacking with atomic distances of
3.009–3.383 Å. Crystal packing diagram demonstrates that
each molecule of 1b (Figure 7) is positioned far from each
other and there is no intermolecular π-π stacking resulting in
the loss of the excited energy, presumably due to the dis-
torted molecular conformation, which is essential for the
efficient solid-state emission.
3.2.5 Photoluminescence properties in PMMA film
Table 4 summarizes photoluminescence data of 1 dispersed
in PMMA film at 298 K under vacuum. As shown in
Figure 5, the emission maxima and spectral shape were al-
most similar, and each spectrum were red-shifted compared
with those of the solids at 298 K and in ETE at 77 K, al-
though the reason is unclear. Short and long lifetimes in the
order of nano- and microseconds, respectively, were ob-
served with the PMMA films as with the solids at 298 K,
indicating that the green emission of the films also consisted
of prompt and delayed fluorescence. In air, the quantum
yields of the films slightly lowered compared with those
under vacuum. The decrease of the luminescence quantum
yields in air should be attributed to the quenching of the
triplet excited state by molecular oxygen, and hence the
values of the decrease, in principle, correspond to the
quantum yields of delayed fluorescence. However, even in
air, the emission components whose lifetimes were in the
order of microseconds were still observed with all of 1. This
means that un-quenched triplet species remain in the PMMA
films in air, and the quantum yields for delayed fluorescence
cannot be simply estimated from the difference of the
quantum yields (∆Φ) between under vacuum (Φvacuum) and in
air (Φair).
3.4 Theoretical calculations
Molecular orbital calculations of 1a–1c were carried out by
DFT method at the B3LYP/cc-pVDZ//B3LYP/cc-pVDZ le-
vel using the Gaussian 09 package (Table 5) [38]. The mo-
lecular structures were optimized using initial structures
based on the molecular structure of 1b determined by X-ray
analysis. Each highest occupied molecular orbital (HOMO)
Table 4 Photoluminescence data of 1 dispersed in PMMA film at 298 K
under vacuuma)
1
λem (nm)
523
Φvacuum
0.30
τ1 (ns)
9.7
τ2 (μs)
2.7
∆Φb)
0.04
0.04
0.16
0.02
1a
1b
1c
1d
531
0.34
3.8
4.5
522
0.39
5.1
3.6
531
0.30
4.1
3.2
a) Excitation was affected by UV irradiation at 350 nm for 1a, 1b, and
1d, and 360 nm for 1c. b) ∆Φ=Φvacuum–Φair.
Figure 6 Molecular structure of 1b. (a) Side view and (b) top view (color
online).
Figure 5 Fluorescence spectra and luminescent images of 1 in PMMA
film at 298 K under vacuum (color online).

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Figure 8 LUMO and HOMO drawings of 1a–1c.
Figure 7 Crystal packing diagram of 1b (a view from a axis). Each
molecule is color-coded based on symmetry operations (color online).
structure of 1.
3.5 Applications to temperature sensing
Table 5 Calculated energies of LUMO, HOMO, S1, and T1 and their
energy gaps of 1a–1ca)
Temperature sensing that uses organic luminophores has
attracted broad attention in various fields because molecular
thermometer can measure temperature in a very small space
such as a living cell and a microfluidic channel [39–45]. In
view that the excited triplet states are very sensitive to
temperature, we measured the lifetime of 1b in powder at
temperatures ranging from –80 to 80 °C. Figure 9 shows the
dependence of logarithm value of delayed fluorescence
lifetime on temperature. The relationship can be expressed as
negative direct function with a coefficient of determination
being 0.988. The finding that the aggregated 1b can sense
temperature with high accuracy opens the possibility of 1 as
a molecular thermometer for measurement of the tempera-
ture of living cells where organic luminophores definitely
form aggregates due to the aqueous conditions.
1
1a
1b
1c
ELUMO (eV)
EHOMO (eV)
∆ELH (eV)b)
–1.74
–5.16
3.42
–1.52
–5.10
3.58
–1.67
–4.98
3.31
∆ELH (nm)
363/373
347/365
375/388
/λabs (nm)b)
ES1 (eV)
ET1 (eV)
∆EST (eV) c)
2.755
2.671
0.084
2.916
2.794
0.122
2.650
2.575
0.075
a) Calculated at the B3LYP/cc-pVDZ//B3LYP/cc-pVDZ level. b) ∆ELH
=
ELUMO–EHOMO. c) ∆EST=ES1–ET1.
is localized over one Ar2N moiety that does not form in-
tramolecular π-π stacking and a central benzene ring
(Figure 8). It should be noted that another Ar2N moiety does
not participate in the HOMO. The lowest unoccupied mo-
lecular orbitals (LUMOs) are developed over a central ben-
zene ring and an aroyl group. Thus, the HOMOs and LUMOs
are separated with little overlap on the central benzene ring.
Time-dependent (TD) DFT calculations of the optimized
structures indicate that the lowest energy transitions are as-
signable to the transition from the HOMOs to LUMOs. The
calculated larger and smaller HOMO-LUMO energy gaps
(∆ELH) of 1b and 1c, respectively, with respect to 1a are
matched with the trend of their absorption maxima. Hence,
the optical excitation, i.e., absorption, of 1 is concluded to
involve ICT from one Ar2N moiety to an aroyl group. The
calculated values of ∆EST are 0.075 to 0.122, which are small
enough to facilitate RISC and emergence of TADF. These
calculations allow us to confirm the validity of the ICT ex-
citation mechanism and molecular orbital calculations using
(TD)-DFT method are reliable for elucidating the electronic
4 Conclusions
We have demonstrated that 2,6-bis(diarylamino)benzo phe-
Figure 9 Temperature dependence of the DF lifetime of 1b.

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prompt and delayed fluorescence. The delayed fluorescence
is also observed when the benzophenones are dispersed in
PMMA films. The absorption process occurred via in-
tramolecular charge-transfer from one diarylamino moiety to
an aroyl group. In other words, the second amino moiety
does not be involved as a donor in the photophysical pro-
cesses. This finding may lead to new guiding principle for
the molecular design of organic luminophores that exhibit
aggregation-induced delayed fluorescence. Further re-
searches on the design and development of novel lumino-
phores with AIE character are under way.
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Acknowledgements This work was supported by Grants-in-Aid for JSPS
KAKENHI (15H03795), MEXT KAKENHI 15K13671, the Nagase Science
and Technology Foundation, and the Ogasawara Foundation for the Pro-
motion of Science and Engineering.
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http://chem.scichina.com and http://link.springer.com/journal/11426. The
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