Photochemical formation of thiirene and thioketene in 1,2,3-thiadiazoles with phenyl substituents studied by time-resolved spectroscopy

Article abstract of DOI:10.1039/c3pp25453d

Photochemistry of 4-phenyl-1,2,3-thiadiazole (PT) and 4,5-diphenyl-1,2,3- thiadiazole (DPT) in solution was studied at room temperature using UV-vis and IR transient absorption spectroscopies (λ_ex = 266 nm). Ultrafast techniques show a very fast rise (<0.3 ps) of thiirene and thioketene species, formed from 1,2,3-thiadiazoles in the singlet excited state. The remarkable unimolecular stability of thiirenes in solution is observed. On a millisecond time scale thiirenes with phenyl substituents undergo an intermolecular reaction (dimerization of thiirene-thioketene complexes) leading to 1,3-dithiole derivatives.

Full text of DOI:10.1039/c3pp25453d

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PAPER
Photochemical formation of thiirene and thioketene in
1,2,3-thiadiazoles with phenyl substituents studied by
time-resolved spectroscopy†
Cite this: Photochem. Photobiol. Sci., 2013,
12, 895
Gotard Burdzinski,*a Michel Sliwa,b Yunlong Zhang,c Stéphanie Delbaere,d
Tomasz Pedzinskie and Julien Réhaultf
Photochemistry of 4-phenyl-1,2,3-thiadiazole (PT) and 4,5-diphenyl-1,2,3-thiadiazole (DPT) in solution
was studied at room temperature using UV-vis and IR transient absorption spectroscopies (λex = 266 nm).
Ultrafast techniques show a very fast rise (<0.3 ps) of thiirene and thioketene species, formed from 1,2,3-
thiadiazoles in the singlet excited state. The remarkable unimolecular stability of thiirenes in solution is
observed. On a millisecond time scale thiirenes with phenyl substituents undergo an intermolecular reac-
tion (dimerization of thiirene–thioketene complexes) leading to 1,3-dithiole derivatives.
Received 31st December 2012,
Accepted 12th February 2013
DOI: 10.1039/c3pp25453d
www.rsc.org/pps
We choose to study 4-phenyl-1,2,3-thiadiazole (PT) and 4,5-
diphenyl-1,2,3-thiadiazole (DPT) precursors. The advantage of
1. Introduction
The compounds 1,2,3-thiadiazoles and their derivatives make phenyl substituents over simpler groups should be the pres-
an important class of molecules in organic synthesis1,2 and ence of red-shifted electronic transitions of intermediates
medicinal chemistry,2 and their rich photochemistry has been facilitating their detection with time-resolved UV-vis spec-
studied by chemical, physical, and computational methods.3 troscopy. The aim of our study was to check if Scheme 1,
The light irradiation of 1,2,3-thiadiazoles can result in molecu- initially proposed for MCT, can be also applied for other
lar nitrogen extrusion and formation of intermediates such as derivatives of 1,2,3-thiadiazoles and be a generalized scheme
thiirenes and thioketenes. Both species have been directly for such type of compound. Additionally, to the best of our
characterized in numerous studies in cryogenic matrices.3–8 knowledge, thiirenes with phenyl substituents have never been
Hypothetical intermediacy of 1,3-diradicals and thiocarbenes observed. The question is how phenyl substituents will affect
as precursors of thiirenes or thioketenes is not clear.3 The thiirene formation and its unimolecular stability. On the basis
mechanistic details of the photoreaction have been recently
studied by time-resolved spectroscopy for 4-methyl-5-
carboethoxy-1,2,3-thiadiazole (MCT) in solution phase
(Scheme 1).9 When extrusion of molecular nitrogen from 1,2,3-
thiadiazole takes place, the structure immediately collapses to
thiirene. Thioketene is formed in a hetero-Wolff rearrange-
ment, possibly in a concerted process without intervention of
thiocarbene.9
aQuantum Electronics Laboratory, Faculty of Physics, Adam Mickiewicz University in
Poznan, 85 Umultowska, Poznan 61-614, Poland. E-mail: gotardb@amu.edu.pl
bUniversité Lille Nord de France, CNRS-UMR 8516, Lille1, LASIR, F-59655 Villeneuve
d’Ascq, France
cKoch Institute for Cancer Research, Massachusetts Institute of Technology,
77 Massachusettes Ave, Cambridge, MA 02139, USA
dUniversité Lille Nord de France, CNRS UMR 8516, UDSL, F-59006 Lille, France
eFaculty of Chemistry, Adam Mickiewicz University in Poznan, 89b Umultowska,
61-614 Poznan, Poland
fPhysikalisch-Chemisches Institut, Winterthurerstrasse 190, CH-8057 Zürich,
Switzerland
†Electronic supplementary information (ESI)
available. See DOI:
Scheme 1 Thiirene and thioketene formation upon photolysis of 1,2,3-
10.1039/c3pp25453d
thiadiazoles.
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of the studies in cryogenic matrices, electron-withdrawing
groups (CO2C2H5, CO2CH3, CH3CO, CF3) have been proposed
2. Experimental
to stabilize the ring, by lowering the π-electron density on the PT (4-phenyl-1,2,3-thiadiazole) and DPT (4,5-diphenyl-1,2,3-
carbon–carbon double bond in thiirenes.3 Indeed, methyl, thiadiazole) were provided by Cayman Chemical Company.
carboethoxy-thiirene has been found to present a high unimo- Diphenylacetylene, tetraphenyl-thiophene, acetonitrile (spec-
lecular stability, as its decay in acetonitrile was caused by troscopic grade), chloroform (spectrometric grade), deuterated
dimerization on a millisecond time scale.9
acetonitrile-d3 (99.8 atom% D), deuterated methanol-d1 (99.5
Photochemistry of PT and DPT has been already studied. atom% D) and deuterated chloroform-d1 were purchased from
The redistribution of a 13C label has been examined for Sigma-Aldrich and used without further purification. The
4-phenyl-[13C]-l,2,3-thiadiazole. Upon photolysis (λ > 230 nm in ultrafast infrared laser system and broadband UV-vis femto-
benzene or methanol) the position of a 13C label was comple- second transient absorption set-up have been described
tely retained in thioketene, implying that thiirene could not elsewhere.19–21 The pump pulse energy was about 3 μJ (IR
have been its precursor, in agreement with the proposed detection) and 10 μJ (UV-vis) at the sample position. The
Scheme 1.10,11 The thioketene intermediates have been charac- sample concentration was adjusted for an optical density of
terized by a weak electronic transition in the visible range 1.0 at the excitation wavelength. A sample volume of 2 mL (IR)
(λmax = 624 nm, log ε = 2.5 for DPT, λmax = 596 nm for PT), at and 50 mL (UV-vis) was continuously circulated through the
wavelengths below 300 nm, stronger electronic transitions are sample cell to ensure that the fresh sample was photoexcited.
located.12 Thioketenes possess
a convenient IR marker The entire set of pump–probe delay positions was repeated at
(νCvCvS stretching vibration, in dichloromethane at least three times, to ensure data reproducibility. To avoid
1725 cm−1 for DPT, in trichlorofluoromethane at 1745 cm−1 rotational diffusion effects, the angle between polarizations of
for PT).12–14 The main photoproduct of PT and DPT photolysis the pump beam and the probe beam was set to the magic
in benzene solution has been identified as 1,3-dithiole, while a angle (54.7°). Kinetic traces were analyzed by fitting to a sum
small yield of 1,4-dithiine has been observed for DPT.15,16
of exponential terms. Convolution with a Gaussian response
function was included in the global fitting procedure. The
instruments response was approximately 300 fs (fwhm). All
experiments were performed at room temperature.
The nanosecond UV-vis transient absorption system has
been described elsewhere.22 Samples were placed in a quartz
cell (10 mm × 10 mm) at concentrations adjusted for absorp-
tion of about 1 at 266 nm excitation wavelength. The influence
of sample irradiation with UV xenon light (266 nm, bandwidth
10 nm, cell with a magnetic stirrer) on stationary absorption
Thiirenes with phenyl substituents have not been character- UV-vis spectra was also checked with a Jasco V-550 spec-
ized in the literature, but the intermediacy of diphenyl-thiirene trometer. Stationary IR spectra were recorded using a Bruker
has been considered in the photoreaction of the mesoionic Tensor 27 FT-IR spectrometer.
2,5-diphenyl-1,3-dithiol-4-one in benzene (Scheme 2).17,18
NMR spectra were recorded on a Bruker Avance 500 MHz
In this paper, results of transient absorption IR and UV-vis spectrometer (1H 500 MHz, 13C 125 MHz) or 300 MHz (1H
spectroscopies, supported by calculations, show that the ultra- 300 MHz, 13C 75 MHz) equipped with a TXI or QNP probe
fast processes (<0.3 ps) lead to formation of thiirene or thio- using standard sequences (1H, 1D-Noesy, 13C), 2D 1H–13C
1
ketene from the initially photoexcited 1,2,3-thiadiazole, HSQC (Heteronuclear Single Quantum Coherence), 2D H–13C
allowing us to propose a general photo-dynamic scheme. To HMBC (Heteronuclear Multiple Bond Correlation). Data acqui-
our best knowledge, this work is the first report on detection sition and processing were performed with Topspin 2.1 soft-
and characterization of thiirenes with phenyl substituents.
ware (Bruker). Irradiation with 254 nm light in rotating quartz
Scheme 2 Hypothetical formation and decay of thiirenes.
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NMR tubes (5 mm) was achieved at 295 K with a Bioblock convolved with the instrument response function (IRF, fwhm
Scientific VL-6LC lamp (12 W). Irradiation with 313 nm light 300 fs) yields a time-constant <300 fs and a longer one in the
was carried out directly in the NMR tube in a home-built range 1.5–4.7 ps (Fig. S2†). The short component can be
apparatus with a 1000 W high-pressure Hg–Xe lamp equipped assigned to the lifetime of PT in the excited state, the slower
with two filters: Schott 11FG09 (259 < λ < 388 nm with λmax
330 nm, T = 79%), and interferential one (λmax = 313 nm and nanosecond transient absorption studies, the thiirene band at
T = 16%). 400 nm is also clearly observed at a delay time of 0.1 ms
=
one to the vibrational relaxation of nascent thiirene species. In
DFT and TD-DFT calculations were performed using the (Fig. 1b). On a ms time scale, the thiirene absorption band
Gaussian 03 suite of programs at The Ohio Supercomputer undergoes a decay, which is accompanied by a rise of a new
Center. Geometries were optimized at the B3LYP/6-31G(d) level band peaking at 350 nm and an isosbestic point at 385 nm is
of theory with single-point energies obtained at the B3LYP/ observed. This 350 nm absorption band corresponds to a per-
6-311+G(d,p)//B3LYP/6-31G(d) level of theory. Vibrational fre- sistent photoproduct, on the basis of stationary UV-vis absorp-
quency analyses at the B3LYP/6-31G(d) level were used to verify tion studies performed for irradiated solution (λ = 266 nm,
that stationary points obtained corresponded to the energy Fig. S1†). This stable photoproduct band can tentatively be
minima. The calculated frequencies were scaled by a factor of assigned to 2-benzylidene-4-phenyl-1,3-dithiole by analogy to
0.9614.23 The electronic spectra were computed using time- the results reported by Kirmse and Horner (product character-
dependent density functional theory of Gaussian 03 at the ized by a maximum at 354 nm with log ε = 4.33 in dioxane,15
B3LYP/6-311+G(d,p) level, and 20 allowed electronic transitions and at 244 nm with log ε = 4.34) and in agreement with
were calculated.
TD-DFT calculations (Tables S6 and S8†). To confirm the
identification of the persistent product, 1H NMR measure-
ments were performed for an irradiated solution of PT in
benzene-d6 (λ = 254 nm). Two types of new signals appeared at
6.60 and 5.83 ppm, and at 6.54 and 5.93 ppm, with the same
rate of formation (Fig. S3†). They were assigned to the cis and
trans 1,3-dithiole isomers.
3. Results and discussion
3.1. PT
The stationary UV-vis spectrum of PT in acetonitrile is shown
in Fig. S1.† On the basis of TD-DFT calculations (Table S2†),
we can assume that 266 nm excitation will generate a set of
highly excited singlet states. Fig. 1a shows results for PT in
acetonitrile recorded by ultrafast UV-vis transient absorption
spectroscopy. Initially,
a broad absorption band with a
maximum at 380 nm is observed, which can be assigned to PT
in the singlet excited state. This band undergoes a fast decay
and at delays of few ps, a band peaking at 400 nm is found.
We attribute the 400 nm band to the phenyl-thiirene on the
basis of TD-DFT calculations using the PCM model (402.3 nm,
FT-IR measurements were also performed for the irradiated
S0→S1, f = 0.1271, Table S4†). In a 6–50 ps time window thi- solution (λ = 266 nm) of PT in deuterated acetonitrile
irene band narrowing is observed due to vibrational cooling, at (Fig. S4†). The IR spectrum of persistent photoproducts agrees
longer delays up to 2 ns the thermalized thiirene absorption with reported IR frequencies for both isomers of 2-benzyli-
band does not change shape and intensity. Fitting of kinetics dene-4-phenyl-1,3-dithioles (1565s, 1550m, 1480m and 1430s
of UV-vis transient absorption at selected wavelengths 350, cm−1, recorded in KBr),24 in fair agreement with theoretical
400, 430, and 500 nm with a double-exponential function predictions (Tables S5 and S7†).
Fig. 1 Time-resolved UV-vis transient absorption spectra recorded for PT in acetonitrile after photoexcitation at 266 nm in (a) 0–100 ps (b) 0.1–90 ms time
windows.
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Fig. 2 Time-resolved IR transient absorption spectra recorded for PT in deuterated acetonitrile (a) and methanol MeOD (b), after photoexcitation at 266 nm.
Fig. 3 Time-resolved UV-vis transient absorption spectra recorded for DPT in acetonitrile after photoexcitation at 266 nm in (a) 0–20 ps (b) 1.3–150 ms time
windows.
Since thiirene–thioketene dimerization leads to 1,3-dithiole formed with a similar yield in CH3OD (Fig. 2b), so this result
photoproducts,9 one can expect to observe thioketene absorp- favours an RIES process under the assumption that hypotheti-
tion in time-resolved studies. Phenyl-thioketene is known to cal thiocarbonyl carbene species can be efficiently trapped by
show an absorption band at 596 nm measured in dichloro- the solvent despite the competition of a fast hetero-Wolff
methane12 at T ∼ 80 °C (Table S10†). However this absorption rearrangement process.
band is weak (n→π* electronic transition), and we failed to
Femtosecond UV-vis and IR data show the presence of two
detect it in UV-vis time-resolved experiments. For thioketene competitive ultrafast reaction channels in the 1,2,3-thiadiazole
detection a suitable method is the time-resolved IR spec- excited state: formation of thiirenes and thioketenes. Note that
troscopy. Phenyl-thioketene is expected to show a strong IR the interpretation of time-resolved UV-vis and IR data for PT is
transition at about 1745 cm−1 on the basis of the literature12 analogous as for MCT.9
and calculations (1739 cm−1, Table S9†). Experiments using
266 nm excitation with IR detection for PT in acetonitrile-d3
3.2. DPT
were performed to detect thioketene species. Fig. 2a shows
that at initial delays, a positive band is present at about
1660 cm−1 which can be assigned to the vibrationally hot thio-
ketene. This species undergoes vibrational relaxation as con-
firmed by band-narrowing and the spectral frequency up-shift
of the initial positive IR band, over a 100 ps time window
(Fig. 2a). The hot thioketene shows a significant band area at
early times (∼1.8 ps), so RIES (rearrangement in the excited
state) might be an important channel for thioketene gener-
ation. The RIES has been proposed as an important reaction
channel for diazo carbonyl compounds on the basis of the sig-
nificant IR band area of photoproduced hot ketene species at
early delays (∼1 ps), and by the observation of a “nontrappable
carbene” route to rearranged products.25,26 Thioketenes are
The extra phenyl group in DPT shifts the stationary UV-vis
absorption band to longer wavelengths in comparison to that
of PT. On the basis of TD DFT calculations (Table S12†) we can
assume that 266 nm excitation results in formation of a highly
excited state of DPT. Ultrafast UV-vis transient absorption
measurements were performed for DPT in acetonitrile (λexc
=
266 nm). At early delays a broad positive absorption band
peaking at 380 nm is observed, corresponding to DPT in the
singlet excited state (Fig. 3a). At longer delays a 440 nm
absorption band is present, which can be assigned to diphe-
nyl-thiirene on the basis of TD DFT calculations using the
PCM model (strong transition at 482.1 nm, S0→S1, Table S14†).
Analysis of kinetic traces at 380, 445 and 500 nm reveals that
the best fits are found using
a biexponential function
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convoluted with the instrument response function (Fig. S5†). of diphenyl-thiirene (Scheme 2). The FT-IR spectrum recorded
The fast component determined is close to IRF (∼300 fs), the on the UV irradiated solution of DPT in a deuterated solvent is
second component varies from 6 to 17 ps and depends on the less indicative (Fig. S7†), because it can be potentially assigned
wavelength. These two components reflect the short lifetime of to four species: tetra-phenyl-thiophene, diphenylacetylene, 1,4-
DPT in the excited state and vibrational cooling of the diphe- dithiine and 1,3-dithiole derivatives. The first two compounds
nyl-thiirene, respectively. Results of nanosecond photolysis at were proposed on the basis of a comparison of the spectra of
266 nm (Fig. 3b) reveal that in a 150 millisecond time window photoproducts and the authentic samples (Fig. S7†); for tetra-
thiirene decay at 440 nm is accompanied by a rise of the new phenyl-1,4-dithiine the IR bands have been reported at 1485w
band at 350 nm. This 350 nm band can be assigned to a 1,3- and 1440w cm−1 27
for 4,5-diphenyl-2-(diphenylmethylene)-1,3-
;
dithiole stable photoproduct on the basis of the reported dithiole the expected frequencies should be close to those
absorption band with a maximum at 347 nm and log ε = 4.38 reported for 2-benzylidene-4-phenyl-1,3-dithiole, i.e. 1565s,
in benzene,15 and TD DFT calculations predicting a strong 1550m, 1480m and 1430s cm−1 in KBr.24 NMR spectra of the
S0→S3 transition at 362.5 nm (Table S16†). Stationary UV-vis irradiated solution of DPT in deuterated benzene (C6D6, λ =
absorption spectra were recorded for fresh and irradiated solu- 254 or 313 nm) show a complex mixture of persistent photo-
tions (at 266 nm, 3 min) of DPT in acetonitrile (Fig. 4). Inter- products (Fig. S8†). Formation of diphenyl-acetylene and tetra-
estingly, with no further UV irradiation, we can observe the phenyl-thiophene was confirmed by recording NMR spectra
evolution of UV-vis absorption spectra in a 30 minutes time for the authentic samples in C6D6 (Fig. S8†). Presumably NMR
window and the initial yellow colour of the irradiated solution data for the irradiated solution show also 4,5-diphenyl-2-
disappears. There is a decay of bands at 440 nm and 270 nm (diphenylmethylene)-1,3-dithiole and phenyl(2-phenylethynyl)-
(both correspond to thiirenes, Table S14†), and a gentle rise at sulfane. The presence of the latter compound can be expected,
300 nm. The rising band at about 300 nm can be assigned since ethynyl mercaptan was observed in photolysis of simple
to tetraphenyl-1,4-dithiine (in agreement with TD DFT 1,2,3-thiadiazoles (studies in a cryogenic matrix).5 For tetra-
calculations predicting a strong S0→S3 transition at 307.1 nm, phenyl-1,4-dithiine NMR data are known in deuterated chloro-
f = 0.3132, Table S18,† and a reported shoulder at 310 nm in form,27 however we have not detected such signals for the
chloroform27) or tetraphenyl-thiophene (its absorption spec- irradiated solution of DPT in CDCl3.
trum is shown in Fig. S6†). The latter scenario can be proposed
The above proposed formation of 1,3-dithioles requires the
by analogy to thiirene–thiirene dimerization observed for an presence of a thioketene precursor, which undergoes reaction
MCT precursor.9 The process of thiirene decay can be with thiirenes. To detect the diphenyl-thioketene absorption
described by a second order reaction, the kinetic trace at band, the time-resolved IR spectroscopy was used. The diphe-
440 nm is shown in the inset of Fig. 4. Moreover, examination nyl-thioketene absorption band is expected at ∼1725 cm−1 on
of UV-vis absorption spectra of irradiated DPT solution reveals the basis of reported data in dichloromethane12 and calcu-
a weak contribution of diphenyl-acetylene, confirmed by a lations (1719 cm−1, Table S19†). The recorded time-resolved
characteristic band at 279 nm (Fig. 4 and S6†). One can transient absorption spectra of diphenyl-thioketene in MeOD
assume that diphenyl-acetylene is formed upon UV-irradiation are shown in Fig. S9.† Similarly as for phenyl-thioketene, ther-
malized diphenyl-thioketene band intensity is not sensitive to
solvent (chloroform vs. methanol). One can expect a gentle
decrease in the quantum yield of molecular nitrogen extrusion
for DPT compared to PT, since a more complex structure and a
smaller ΔE(S1–S0) energy gap may facilitate the internal conver-
sion process (S1→S0). However, a substantial decrease in the
absorption band amplitude of thermalized diphenyl-thio-
ketene in comparison to that recorded for phenyl-thioketene
(Fig. 2b and S9†) is observed (factor ∼4). The calculations
predict a similar IR oscillator strength for both species (Tables
S9 and S19†). A lower yield of diphenyl-thioketene formation
can be explained by a lower migratory ability of phenyl substi-
tuents, when compared to those of H in the Wolff rearrange-
ment process. This is in line with the reported decrease in 1,3-
dithiole formation yield upon going from PT to DPT in
benzene.3 Due to the reduced yield of reaction between
diphenyl-thiirene and diphenyl-thioketene, one can expect that
thiirenes undergo also other reactions (self-dimerization) con-
firmed by detection of tetraphenyl-thiophene. Moreover, large
phenyl substituents slow down diffusion of thiirenes and exert
Fig. 4 Absorption UV-vis spectrum of DPT in acetonitrile (solid black curve).
UV-vis spectra (colored dashed curves) were recorded at different delays for solu-
steric effects on bimolecular reactions, so thiirenes are more
exposed to secondary photolysis leading to diphenylacetylene
tion irradiated with 266 nm (3 min). The inset shows the linearity of kinetic trace
of 1/absorbance traced at 440 nm.
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or phenyl(2-phenylethynyl)sulfane; this hypothesis requires
further investigation.
2 V. A. Bakulev and W. Dehaen, The Chemistry of 1,2,3-Thia-
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3 W. Kirmse, 100 years of the Wolff rearrangement,
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4. Conclusions
4 E. Schaumann, The chemistry of thioketenes, Tetrahedron,
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5 A. Krantz and J. Laureni, Characterization of matrix-
isolated antiaromatic three-membered heterocycles.
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The initial stages of photoreaction in 1,2,3-thiadiazoles can be
described by a general Scheme 1. The results presented in this
paper have shown for the first time the presence of thiirenes
with phenyl substituents in solution. Surprising unimolecular
stability of these thiirene species was observed, as their decay
was caused by intermolecular processes of dimerization: thi-
irene–thioketene (PT, DPT) and thiirene–thiirene (DPT). The
presence of one or two phenyl substituents in thiirene con-
veniently locates its absorption at ∼400 and 440 nm in aceto-
nitrile, respectively. Diphenyl-thioketene is formed at a lower
quantum yield than phenyl-thioketene, because of lower
migratory ability of phenyl substituents when compared to
that of H in the ultrafast Wolff rearrangement process.
Photolysis of PT leads to derivatives of 1,3-dithioles, for DPT, it
results in a complex mixture of persistent products such as
4,5-diphenyl-2-(diphenylmethylene)-1,3-dithiole, tetraphenyl-
thiophene, diphenyl-acetylene and presumably phenyl(2-phe-
nylethynyl)sulfane.
6 A. Krantz and J. Laureni,
A methodology for the
preparation and characterization of three-membered,
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7 A. Krantz and J. Laureni, Matrix photolysis of 1,2,3-thiadia-
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8 M. Torres, A. Clement, J. E. Bertie, H. E. Gunning and
O. P. Strausz, Low-temperature matrix isolation of thiirenes,
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9 G. Burdzinski, M. Sliwa, Y. Zhang and S. Delbaere, Early
events in the photochemistry of 1,2,3-thiadiazole studied
by ultrafast time-resolved UV-Vis and IR spectroscopies,
J. Phys. Chem. A, 2011, 115, 14300–14305.
In future, we would like to study the effect of para substi-
tution in a phenyl ring on 1,2,3-thiadiazoles photochemistry,
using electron-donating and electron-withdrawing sub-
stituents.
10 U. Timm and H. Meier, Markierungsexperimente zur frag-
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11 U. Timm, U. Merkle and H. Meier, Die bildung von
phenylthiiren, Chem. Ber., 1980, 113, 2519–2529.
12 G. Seybold and C. Heibl, Thioketene aus 1,2,3-thiadiazolen
und 1,3-dithietanderivaten, Chem. Ber., 1977, 110,
1225–1238.
13 H. Murai, M. Torres and O. P. Strausz, Detection of
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14 T. Jørgensen, C. T. Pedersen, R. Flammang and
C. Wentrup, Formation of thioketenes by thermal fragmen-
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Acknowledgements
This work was performed under financial support of National
Science Centre in Poland, project N N204 179540. Ultrafast
studies were performed in LASIR at Université Lille 1 Sciences
et Technologies and at University of Zürich. G.B. thanks Pro-
fessor Peter Hamm for providing laboratory access and
measuring time. Support of this work by the Ohio Supercom-
puter Center is gratefully acknowledged. The 500 MHz NMR
facilities were funded by the Région Nord-Pas de Calais
(France), the Ministère de la Jeunesse de l’Education Nationale
et de la Recherche (MJENR) and the Fonds Européens de
Développement Régional (FEDER).
15 W. Kirmse and L. Horner, Photolyse von 1.2.3-thiodiazolen,
Liebigs Ann. Chem., 1958, 614, 4–18.
16 K.-P. Zeller, H. Meier and E. Muller, Zur photolyse von
1,2,3-thiadiazolen I, Tetrahedron Lett., 1971, 6, 537–540.
17 H. Kato, M. Kawamura, T. Shiba and M. Ohta, Photolysis
of mesoionic 2,5-diphenyl-1,3-dithiol-4-one: a probable
4π-antiaromatic intermediate, J. Chem. Soc. D, 1970,
959–960.
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