Photochromic heteroaromatic thiofulgides and dimethoxybutanoic acid lactones

Article abstract of DOI:10.1039/b002033h

Thiofulgides 1, (X = S) cyclise on irradiation with UV light to form thermally stable photochromes 2, (X = S) that absorb at much longer wavelengths than photochromes 2, (X = O), formed from corresponding fulgides 1, (X = O), reverse reactions occur on ex

Full text of DOI:10.1039/b002033h

Photochromic heteroaromatic thiofulgides and dimethoxybutanoic acid
lactones
Matthew Badland, Alison Cleeves, Harry G. Heller,* David S. Hughes and Michael B. Hursthouse
Chemistry Department, Cardiff University, PO Box 912, Cardiff, UK CF1 3TP
Received (in Cambridge, UK) 13th March 2000, Accepted 3rd July 2000
Published on the Web 3rd August 2000
Thiofulgides 1, (X = S) cyclise on irradiation with UV light
to form thermally stable photochromes 2, (X = S) that
absorb at much longer wavelengths than photochromes 2, (X
= O), formed from corresponding fulgides 1, (X = O),
reverse reactions occur on exposure to white light; photo-
chromic thiofulgides are prepared by reaction of fulgides
with sodium hydrosulfide in hot toluene and photochromic
lactones 9 and 12 are prepared by reaction of fulgides with
sodium hydrosulfide in cold methanol followed by cyclisa-
tion with a carbodiimide.
Photochromic heteroaromatic thiofulgides 1, (X = S) are of
special interest because their coloured forms 2, (X = S) have
the potential to show large bathochromic shifts of their long
wavelength absorption bands compared to the coloured forms 2,
(X = O) from corresponding fulgides 1, (X = O). (The effect
of replacement of oxygen by sulfur can be seen in the ultraviolet
spectra of thiomaleic anhydride2 which shows lmax 230 nm
compared to lmax 198 nm for maleic anhydride3.)
Fig. 2 The spectra of compounds 10, 8a (X = O), 8a (X = S), and 8b (X
= S) (lmax 424, 511, 544, and 599 nm respectively) obtained after
irradiation at 366 nm of compounds 9, 4a, 6a (X = S) and 6b (X = S) (1
3 1024 molar solutions in toluene) to the photostationary state, illustrating
the major colour changes which can be achieved by molecular tailoring.
Previous attempts to synthesise photochromic heteroaromatic
thiofulgides by methods used for the preparation of acetic,4
succinic,5 phthalic,6 and dibenzylidenesuccinic thioanhydrides7
were unsuccessful.
We find that (Z)-thiofulgides, (Z)-4-dicyclopropylmethy-
lene[1-(2,5-dimethyl-3-furyl) and (2-methyl-5-phenyl-3-furyl)-
ethylidene]thiosuccinic anhydrides 6a and 6b can be prepared
Fig. 1 The X-ray structure of (Z)-thiofulgide 6a.
DOI: 10.1039/b002033h
Chem. Commun., 2000, 1567–1568
This journal is © The Royal Society of Chemistry 2000
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by boiling (4 h) (Z)-fulgides 3a and 3b (1 g) in toluene with 2–3
eq. of yellow sodium hydrosulfide (Aldrich). They were
obtained as yellow crystals, mp 133 and 147–8 °C respectively,
after purification by column chromatography and crystallisation
from dichloromethane and petroleum. Seven photochromic
thiofulgides have been prepared in yields of ca. 35% by this
general method. Yields depend on the quality of sodium
hydrosulfide, which deteriorates with time.
The structure and stereochemistry of (Z)-thiofulgide 6a was
established by X-ray crystallographic analysis† (Fig. 1).
On irradiation (366 nm), (Z)-thiofulgides 6a and 6b in
toluene isomerised to (E)-thiofulgides 7a and 7b which cyclised
to thermally stable purple and blue photochromes 8a (X = S)
and 8b (X = S), showing bathochromic shifts (40 and 60 nm)
of the maxima of their long wavelength absorption bands
compared to the red and magenta photochromes 8a (X = O) and
8b (X = O) (Fig. 2). On exposure to white light, photochromes
8a (X = S) and 8b (X = S) ring opened to pale yellow (E)-
thiofulgides 7a and 7b. Quantum efficiencies for colouring (Øc)
at 366 nm for (E)-thiofulgides in toluene were less than for
(Z)-Fulgide 3 gave the colourless lactone 12 in 31% yield in
an analogous reaction which cyclised to the pale yellow
photochrome 13 on irradiation at 366 nm.
Lactones 9 and 12 were converted quantitatively into 11 on
boiling with sodium hydrosulfide in MeOH, exemplifying a
convenient method of preparing dimethyl esters from anhy-
drides. All new compounds were fully characterised.
We thank PPG Industries, Pittsburgh, USA and the Brite
Euram Syladec programme for grants to MB and AC re-
spectively and financial support for this programme, and
EPSRC for support for the X-ray crystallographic work.
Notes and references
† Crystal data for 6a: C19H20O3S, M = 328.4, monoclinic, space group
P2(1)/n, a = 10.773(2), b = 7.861(2), c = 19.492(4) Å, b = 92.42(3)°, V
= 1649.2(6) Å3, T = 150(2) K, Z = 4, Dc = 1.323 g cm3, R1 = 0.0686,
wR2 = 0.1179 for all 2349 data and 211 parameters. Data were recorded
using a FAST TV area detector diffractometer and Mo-Ka radiation. CCDC
182/1709. See http://www.rsc.org/suppdata/cc/b0/b002033h/ for crystallo-
graphic files in .cif format.
corresponding (E)-fulgides. Øc for thiofulgide 1 (R1 = R2
=
Me, X = S) was 9% compared to 20% for fulgide 1 (R1 = R2
= Me, X = O). Preliminary studies indicate that bleaching
efficiencies and photochemical fatigue of the photochromes of
thiofulgides were comparable to those of photochromes of the
corresponding fulgides.
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When (E)-fulgide 4a was stirred with sodium hydrosulfide in
MeOH at room temperature, the salt of thioacid 5 was formed
which after treatment with 1-ethyl-3-(dimethylamino)propyl-
carbodiimide HCl, reacted with methanol to give 9 (colourless
crystals, mp 168–9 °C, 33% yield). On irradiation (366 nm),
lactone 9 in toluene cyclised to the thermally stable bright
intensely coloured yellow photochrome 10 which underwent
the reverse reaction on exposure to white light.
6 A. Reissert and H. Holle, Chem. Ber., 1911, 44, 3027.
7 P. A. Davidse and J. L. M. Dillen, Heteroatom. Chem., 1990, 1, 281.
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