Thermally stable fatigue resistant near infrared active photochromic compounds, exemplified by 6-amino-7-cyano-3-(dicyclopropylmethylene)-4-(2,5-dimethyl-3-furyl)-benzofura n-2(3H)-one

Article abstract of DOI:10.1039/b003496g

The title pale yellow photochromic compound 11b in toluene, on irradiation at 366 nm, cyclises to the thermally stable infrared active blue-green photochrome, 8-amino-7-cyano-4,4-dicyclopropyl-3a,4-dihydro-6-hydroxy-2,3a-dimethylnaphtho [2,1-b]furan-5,6-c

Full text of DOI:10.1039/b003496g

Thermally stable fatigue resistant near infrared active photochromic
compounds, exemplified by 6-amino-7-cyano-3-(dicyclopropylmethylene)-4-
(2,5-dimethyl-3-furyl)-benzofuran-2(3H)-one
Harry G. Heller,* David S. Hughes, Michael B. Hursthouse and Neil G. Rowles
Chemistry Department, Cardiff University, PO Box 912, Cardiff, UK CF1 3TP. E-mail: heller@cardiff.ac.uk
Received (in Cambridge, UK) 2nd May 2000, Accepted 15th June 2000
Published on the Web 7th July 2000
The title pale yellow photochromic compound 11b in
toluene, on irradiation at 366 nm, cyclises to the thermally
stable infrared active blue–green photochrome, 8-amino-
7-cyano-4,4-dicyclopropyl-3a,4-dihydro-6-hydroxy-2,3a-di-
methylnaphtho[2,1-b]furan-5,6-carbolactone, 12b which has
a lmax value of 720 nm for its broad long wavelength
absorption band.
ethylidene-4-isopropylidene tetrahydrofurandione 1c and (E)-
3-[2-methyl-5-phenyl-3-thienyl)ethylidene-4-(dicyclopropyl-
methylene)tetrahydrofuran-2,5-dione 1d reacted with mal-
ononitrile and diethylamine in THF to give exclusively
(E)-2-dicyanomethylene derivatives 3a–d which, in toluene,
cyclised to photochromes 4a–d on irradiation at 366 nm. The
thermally stable blue photochromes 4a–d underwent reverse
reactions on exposure to white light. Previous papers1,2 reported
erroneously that E-fulgides (e.g. 1a) gave the corresponding
(E)-5-dicyanomethylene derivatives (e.g. 8a) on reaction with
malononitrile (1 equiv.) and diethylamine (2 equiv.) in THF,
followed by cyclisation with acetyl chloride.
E-Fulgides, (E)-3-[1-(2,5-dimethyl-3-furyl)ethylidene]-4-iso-
propylidenetetrahydrofuran-2,5-dione 1a, (E)-3-[1-(2,5-dime-
thyl-3-furyl)ethylidene]-4-(cyclopropylmethylene)tetrahydro-
furan-2,5-dione
1b,
(E)-3-[2,5-dimethyl-3-thienyl)-
Z-Fulgides 6a–d gave exclusively the corresponding pale
yellow (Z)-5-dicyanomethylene derivatives 7a–d under similar
experimental conditions. The latter, in toluene, isomerised to E-
isomers 8a–d and cyclised to photochromes 9a–d on irradiation
at 366 nm. The thermally stable blue photochromes 9a–d
underwent reverse reactions to pale yellow E-isomers 8a–d on
exposure to white light.
Deprotonation of the methyl group syn to the dicyano-
methylene group in (Z)-2-dicyanomethylene derivative 3b, by
boiling with diisopropylamine in THF, gave anion 5b, which
reacted with the adjacent cyano group to form imine 10b, which
isomerised to 6-amino-7-cyano-3-(dicyclopropylmethylene)-
4-(2,5-dimethyl-3-furyl)-1-benzofuran-2(3H)-ones 11b,† ob-
tained as bright yellow crystals (from chloroform–petrol). Its
structure was confirmed by X-ray crystallographic analysis
(Fig. 1). Amines 11a–d were prepared in a similar manner.
All new compounds were fully characterised. Spectral data,
melting points and yields are given in Table 1.
On irradiation at 366 nm, amines 11a–d in toluene cyclised to
thermally stable blue-green photochromes 12a–d (Table 2)
which underwent the reverse reactions on exposure to white
light.
Photochromes 2a–d, 4a–d, and 9a–d showed bathochromic
shifts when the push-pull effect is enhanced, as reported for
infrared active dyes.3 Photochromes 12a–d have increased
intramolecular charge-transfer character, due to the tendency to
Fig. 1 The X-ray structure of the photochromic compound 11b.
DOI: 10.1039/b003496g
Chem. Commun., 2000, 1397–1398
This journal is © The Royal Society of Chemistry 2000
1397

Table 1 lmax Values for solutions in toluene after photocyclisation, melting points, and yields of photochromic compoundsa
Compound
3a
3b
3c
3d
7a
7b
7c
7d
11a
11b
11c
11d
lmax/nm
Mp/°C
% Yield
318
323
323
341
353
358
335
333
349
374
348
378
153–154 155–156 177–178 150–151 184–185 182–183 177–178 151–152 227–229 180–181 212–214 237–238
62 62 35 49 39 67 35 90 39 65 31 47
a a X = O, R1 = R2 = Me; b X = O, R1 = Me; R2 = cyclopropyl; c X = S, R1 = R2 = Me; d X = S, R1 = Ph, R2 = cyclopropyl.
Table 2 lmax Values for the long wavelength absorption bands of photochromes in toluene after the photocyclisation of precursors, illustrating the major
bathochromic shifts that can be achieved by molecular tailoringa
Photochrome 2a
2b
2c
2d
4a
4b
4c
4d
9a
9b
9c
9d
12a 12b 12c
12d
lmax/nm 496 514 520 566 601 594 598 653 610 634 642 669 698 720 681 776
a a X = O, R1 = R2 = Me; b X = O, R1 = Me; R2 = cyclopropyl; c X = S, R1 = R2 = Me; d X = S, R1 = Ph, R2 = cyclopropyl.
11a–d well suited for optical memory devices and security
printing. The major changes in the spectra of these photo-
chromes by molecular tailoring are illustrated in Fig. 2.
We thank Philips Research, Eindhoven, The Netherlands and
at Redhill, UK and EPSRC for a CASE studentship to N. G. R.
and for support of the X-ray crystallographic work.
Notes and references
† Crystal data for 11b: C22H20N2O3, Mr 360.4, monoclinic, space group
P(2) 1/c, a = 9.372(8), b = 11.198(7), c = 17.679(7) Å, b = 101.06 (4)°,
V = 18212 A3, T = 293(2) K, Z = 4, Dc = 1.315 g cm23, R1 = 0.0380, wR2
= 0.0676 for all 2655 points data and 248 parameters. Data were recorded
Fig. 2 The spectra of compounds 2b, 4b, 9b and 12b (1 3 1024 molar
using a FAST TV area detector diffractometer and Mo-Ka radiation. CCDC
solutions in toluene) after irradiation at 366 nm to the photostationary
182/1692. See http://www.rsc.org/suppdata/cc/b0/b003496g/ for crystallo-
state.
graphic files in .cif format.
1 H. G. Heller, D. S. Hughes, M. B. Hursthouse and K. V. S. Koh, J. Chem.
retain the benzene ring, as indicated by resonance forms 13a–d,
Soc. Chem. Commun., 1994, 2713.
2 Z. Sun, R. S. Hosmane and M. Tadros, Tetrahedron Lett., 1995, 36,
3453.
3 Y. Kubo, F. Mori, K. Komatsu and K. Yoshida, J. Chem. Soc., Perkin
Trans. 1, 1988, 2439.
which results in the broad absorption band in the region
750–800 nm. The spectra of coloured forms, thermal stability,
fatigue resistance and high efficiencies for colouring and
bleaching make the photochromic system based on compounds
1398
Chem. Commun., 2000, 1397–1398