Solid-state photochromism of 5-tert-butyl-2-hydroxyisophthalaldehyde

Article abstract of DOI:10.1246/bcsj.20110394

Colorless crystals of 5-tert-butyl-2-hydroxyisophthalaldehyde change to an orange-red color upon brief exposure to UV-vis radiation (λ> 300 nm). The colored crystals revert to colorless in the dark. X-ray diffraction revealed different packing patterns for the crystals of nonphotochromic and photochromic compounds.

Full text of DOI:10.1246/bcsj.20110394

Short Articles
Bull. Chem. Soc. Jpn. Vol. 85, No. 6, 727-729 (2012)
727
R
R
h
ν
Solid-State Photochromism
of 5-tert-Butyl-2-hydroxy-
isophthalaldehyde
O
H
O
H
dark
H
CH3
O
H
CH2 OH
2
1
R = Me, i-Pr
H
h
ν
Cl
Cl
CH3
O
Koichi Tanaka,*1 Yuta Watanabe,1
Przemysław Kalicki,2 and
H
N
OH
N
dark
Zofia Urbanczyk-Lipkowska*2
Cl
H
O
Cl
H
4
3
1Department of Chemistry and Materials Engineering,
Faculty of Chemistry, Materials and Bioengineering,
Kansai University, Suita, Osaka 564-8680
H3C
H
H3C
O
O
H
h
ν
H
CH2
O
H3C
H3C
CH3
2Polish Academy of Sciences,
dark
X
X
Kasprzaka 44/52, 01-224 Warszawa, Poland
6
5
R = Br, CN, CHO
Received December 19, 2011
E-mail: ktanaka@kansai-u.ac.jp
Scheme 1.
R
R
Colorless crystals of 5-tert-butyl-2-hydroxyisophthal-
aldehyde change to an orange-red color upon brief expo-
sure to UV-vis radiation (- > 300 nm). The colored crystals
revert to colorless in the dark. X-ray diffraction revealed
different packing patterns for the crystals of nonphoto-
chromic and photochromic compounds.
h
ν
O
H
O
H
dark
H
O
O
H
OH
O
H
7
8
a: R = Me d: R = Br
b: R = i-Pr e: R = OMe
c: R = t-Bu
Scheme 2.
Photochromic compounds have received considerable atten-
tion in recent years owing to their potential applications, such as
information storage, electronic display systems, optical switch-
ing devices, ophthalmic glasses, and macroscale mechanical
motion of materials.1 Several types of organic photochromic
compounds, such as azobenzenes, diarylethenes, naphtho-
pyrans, spiropyrans, fulgides, chromenes, and N-salicylidene-
anilines, have been discovered, and their photochromic proper-
ties have been studied.2
7d
7c
However, there are few reports on the solid-state photo-
chromism involved in the photoenolization of carbonyl com-
pounds (Scheme 1). Kumar and Venkatesan reported that some
isophthalaldehydes 13 exhibit photocoloration from colorless
to red upon exposure to sunlight. The red color fades within
approximately 5 min after storage in the dark. Sarkar et al.
first reported the solid-state photochromism of 2,6-dichloro-4-
methyl-3-pyridinecarbaldehyde (3),4 colorless crystals of which
turn deep orange-red on exposure to sunlight. The colored
crystals revert to colorless within approximately 40 min in the
dark. Moorthy reported that some anisaldehydes 52j change
to brick-red color upon brief exposure to UV-vis radiation. The
red color, attributed to (E)-xylylenol 6, persists for approxi-
mately 10 h.
Figure 1. Photographs of 7c and 7d before (left) and after
irradiation (right).
which can potentially be a family of photochromic compounds
(Scheme 2).
All 2-hydroxyisophthalaldehyde derivatives, 7, were synthe-
sized from readily available 4-substituted phenols by the
Duff reaction.6 Upon brief exposure to UV-vis radiation (- >
300 nm), colorless crystals of 5-tert-butyl-2-hydroxyisophthal-
aldehyde (7c) changed to an orange-red color (Figure 1). The
crystals reverted to the colorless form on standing at room
temperature in the dark for approximately 12 h. Figure 2 shows
that the UV-vis absorption changes in the region 400-600 nm
before and after irradiation may be due to the formation of the
(E)-enol 8c. In contrast, the crystals of other 2-hydroxyiso-
phthalaldehyde derivatives 7a, 7b, 7d, and 7e did not exhibit
any photocoloration and no UV-vis spectral changes occurred
after photoirradiation (Figure 2).
During the course of our study on the photochromism of
chiral Schiff-base macrocycles,5 we had the experience of
studying the photochemistry of 2-hydroxyisophthalaldehyde
derivatives 7. Herein, we report on the solid-state photo-
chromism of 5-tert-butyl-2-hydroxyisophthalaldehyde (7c),
Published on the web May 30, 2012; doi:10.1246/bcsj.20110394

728
Bull. Chem. Soc. Jpn. Vol. 85, No. 6 (2012)
© 2012 The Chemical Society of Japan
Figure 5. Herringbone structure observed in the crystal of 7d.
Figure 2. UV-vis spectral changes of 7c (left) and 7d (right)
in the solid state. Successive measurements were recorded
every 10 min from the top (after irradiation of the light
for 10 min) to the bottom (after keeping 12 h in the dark).
Figure 6. Infinite hydrogen-bonded chains in crystals of 7c;
intramolecular H-bond geometry: O5-H5£O3: O5£O3
2.610(5) ¡, H5£O3 1.53(6) ¡, angle 147(5)°; C9-H9£O5:
C9£O5 2.811(6) ¡, H9£O5 2.46(6) ¡, angle 102(4)°;
intermolecular: C8-H8£O4 [x + 1, +y, +z], C8£O4
3.478(6), H8£O4 2.47(6) ¡, angle 161(5)°.
Figure 3. IR spectral changes of 7c before (green) and after
(blue) photoirradiation in KBr pellet.
Figure 7. Hydrogen-bonding pattern in crystals of 7d:
intramolecular O3-H3£O1: O3£O1 2.623(2) ¡, H3£O1
1.87(4) ¡, angle 146(4)°; C5-H5£O3: C5£O3 2.791(3) ¡,
H5£O3 2.48 ¡, angle 100°; intermolecular dimers: O3-
H3£O3 [¹x + 1/2, y + 1/2, ¹z + 1/2], O3£O3 2.974(3)
¡, H3£O3 2.48(4) ¡, angle 117(4)°; Br£Br distance
3.877(2) ¡.
Figure 4. View down the b axis showing the planar
arrangement of 7c molecules.
of compounds 7c and 7d revealed planar (Figure 4) and
herringbone (Figure 5) arrangements of the molecules, respec-
tively. The geometry of intra- and intermolecular hydrogen
bonds is shown in Figure 6 (7c) and Figure 7 (7d). The inter-
molecular hydrogen bonds and intermolecular nonbonding
contacts in both compounds are within the upper limits. The
Br£Br distance is slightly above the higher limit than that
reported by Navon et al. (3.7 ¡ max).7 One can assume that
the electronic structure of the phenol ring differs because of
presence of the electron-donating group in 7c (t-Bu) and/or
weakly electron-withdrawing group (Br, 7d). Indeed, the
phenol proton in 7d is located closer to the phenol-oxygen
atom O3, whereas in 7c, it is localized between the hydroxy
and aldehyde oxygen atoms.
With the aim of understanding the mechanism of the
photochromism of 7c, we investigated the IR spectra of 7c
before and after photoirradiation (Figure 3). After irradiation,
a new sharp band attiributable to the ¯C-O band for an enol
form appeared at 1086 cm¹1. However, there are no significant
changes in another region of the spectra.
Crystals of 7c and 7d suitable for X-ray analysis were
obtained by recrystallization from cyclohexane, and were
investigated by X-ray crystallography to elucidate the structural
factors that explain the presence of photochromic properties
only in the crystals of 7d. The crystal lattice of both com-
pounds is modulated by the presence of only one formal
hydrogen-bond donor (phenolic H-atom) and three hydrogen-
bond acceptors. This favors the presence of two intramolecular
hydrogen bonds: one between the hydroxy H-atom and one of
the aldehyde oxygen atoms, and the other between the phenol
oxygen and the H-atom of the second aldehyde group. Crystals
In addition, molecules in 7d form dimeric structures, in
which geometric measures for the intermolecular hydrogen
bond is ideal (O3-H3£O3 angle is only 117°, Figure 7);
however, the O3£O3 distance is sufficiently short to facilitate
proton exchange.

K. Tanaka et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 6 (2012)
729
The presented data show that in the case of photochromic
compound 7c, infinite linear hydrogen bonding is observed,
whereas in case of photoinert derivative 7d hydrogen bonds
are localized to the dimeric system. It is possible that although
crystal irradiation excites molecules of both compounds,
excited state in the case of compound 7c is somehow better
stabilized and can be experimentally detected. The unusually
stable photo-enol of 8c compared to Kumar and Venkatesans’
compounds may be due to the intra- and intermolecular hydro-
gen bonding.
In summary, we have observed the solid-state photochro-
mism of 5-tert-butyl-2-hydroxyisophthalaldehyde (7c), a new
family of photochromic compounds. On the basis of avail-
able crystallographic data and inspection of reflectance FT-IR
spectra for monocrystals before and after irradiation, it is
difficult to predict whether the solid-state photochromism of 7c
is derived from inter- or intramolecular proton hopping. Further
studies on the mechanism of this type of photochromic com-
pound are currently underway.
¢ = 96.979(1)°; V = 777.64(3) ¡3, F(000) = 448, Dcalcd
=
1.956 Mg m¹3, ®(Cu K¡) = 6.910 mm¹1; monoclinic space
group P21/n, Z = 4. A total of 6727 reflections were collected,
1357 of which were unique with R(int) = 0.0319. Multiscan
absorption correction was applied with Tmin = 0.1667 and
T
max = 0.8628. Final R1 = 0.0827 and wR2 = 0.227 for 1233
reflections with I > 2·(I). CCDC-856311 and CCDC-856310
contain the supplementary crystallographic data for 7c and
7d, respectively. These data can be obtained free of charge
at “http://www.ccdc.cam.ac.uk/conts/retrieving.html” (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge, CB2 1EZ, U.K.; E-mail: deposit@ccdc.cam.ac.uk).
This work was supported by Grants-in-Aid for Scientific
Research on Priority Area “New Frontiers in Photochromism
(No. 471)” from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan.
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Experimental
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3
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6
1029.
7
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8