Aromatic Thiones Research Articles

Selenium- and tellurium-bridged heteromerous overcrowded bistricyclic aromatic enes with central six-member and seven-member rings

A series of selenium-bridged and tellurium-bridged heteromerous bistricyclic aromatic enes (BAEs) 15–25 with six-member and seven-member central rings have been synthesized by Barton–Kellogg olefination, twofold extrusion coupling method between tricyclic aromatic thiones and tricyclic aromatic diazo derivatives. The crystal structures of thioxanthenylidene-anthracenone (15), selenoxanthenylidene-anthracenone (20), and telluroxanthenylidene-anthracenone (21) were determined. The ordered crystal structure of 21 showed a very high degree of folding of the telluroxanthenylidene moiety (58.5°) and very short intramolecular Te···C9′ contact distance, indicating >20 % penetration which may reflect secondary nonbonding interactions and lack of aromatic telluroxanthenylium-anthracenolate contribution. The BAEs were subjected to a 1H-, 13C-, 77Se-, and 125Te-NMR spectroscopic study. The 1H-NMR spectra indicated anti-folded conformations in solution. The measured pronounced downfield 77Se- and 125Te-NMR shifts in 20 and 21, relative to the corresponding spectra of homomerous BAEs diselenoxanthylene (7) and ditelluroxanthylene (8), may be due to the proximity of the Se and Te bridges to the carbons of the central enes in the anti-folded conformations. This deshielding effect was larger in 21 than in 20, δ(125Te)/δ(77Se) = 1.53, a ratio higher than in any other member of the series.

ChemInform Abstract: Photochemistry of Aromatic Thiones in Their S2 and T1 States. Role of Triplet Self-Quenching and Excimer Formation.

The quantum yields of photodecomposition of xanthione (XT), 4H- 1-benzopyran-4-thione (BPT) and 4H-pyran-4-thione (PT) subsequent to excitation to their S2 and S1 states have been measured as a function of thione concentration in inert perfluoroalkane solvents. The quantum yields of intramolecular photodecomposition of these thiones in S2 are immeasurably small. Intermolecular processes dominate the photochemical removal of the triplet states even at very low ( < 10–5 mol dm–3) thione concentrations. In inert perfluoroalkane solvents a photochemical channel in the diffusion-controlled triplet self-quenching process is responsible for the removal of the thione. A mechanism involving the intermediacy of triplet excimers is proposed.

Fluoride‐Assisted Trifluoromethylation of Aromatic Thiones with (Trifluoromethyl)trimethylsilane.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Fluoride-assisted trifluoromethylation of aromatic thiones with (trifluoromethyl)trimethylsilane

In the presence of a stoichiometric amount of Bu 4NF·3H 2O, (trifluoromethyl)trimethylsilane reacts with aromatic thiones in both thiophilic and carbophilic ways to deliver, in medium yield, a mixture of (trifluoromethylthio)diarylmethane and 1,1-diaryl-2,2,2-trifluoroethanethiol, the former product being the major one.

Electronic band states of long-range ordered aromatic thione molecules assembled on Cu(100)

Two-dimensional long-range ordered organic molecule layers can be achieved by depositing thiols on single crystalline surfaces. The aromatic thione 2-mercaptobenzoxazole (MBO) molecule $({\mathrm{C}}_{7}{\mathrm{H}}_{5}\mathrm{NOS})$ presents a S-containing head which reacts with the Cu surface, and an aromatic ring originating lateral van der Waals interactions and molecular self-organization. A long-range-ordered $p(2\ifmmode\times\else\texttimes\fi{}2)$ structure of MBO on Cu(100) is obtained, by MBO sublimation in highly controlled ultrahigh-vacuum conditions. The MBO molecular orbitals and interface electronic levels have been identified, also comparing the room-temperature experiment with the low-temperature (100 K) physisorption data, by angular-resolved high-resolution UV photoelectron spectroscopy. The role of S as a chemical hook for the molecule to the Cu surface is evidenced, and comparison with similar compounds suggests that the adsorption mechanism and the related electronic structure are rather general results for \ensuremath{\pi}-conjugated molecules with a S-containing head. We give striking evidence of energy-band formation of MBO-Cu interaction states, bringing to light molecule-Cu extended hybrid bands, with a bandwidth of 120 meV along one main azimuthal symmetry direction of the surface Brillouin zone.

The relaxation of electronically excited molecules: Effects of alkyl substitution on the S2 and T1 states of benzopyranthione in solution

The effects of n-alkyl group substitution on the photophysics, photochemistry and spectroscopy of benzopyranthione (BPT), a rigid model aromatic thione, have been investigated. The absorption, emission and excitation spectra of BPT and its 2-substituted n-C4H9 (I) and n-C10H21 (II) derivatives, their S2 → S0 fluorescence and T1 → S0 phosphorescence quantum yields and their S2 and T1 lifetimes have been measured in several solvents, in the presence and absence of oxygen. Perfluorinated solvents have been used to minimize the effects of solute–solvent interactions on the excited state dynamics. The rate constants of radiative and non-radiative decay of the S2 and T1 states and of their bimolecular quenching by molecular oxygen and by ground state thione have been obtained. The spectra of I and II are nearly identical in every respect, except that the S2←S0 absorption spectrum of II exhibits a greater absorbance on its red edge, attributable to its larger density of low-frequency torsional states. The expected effect of intramolecular interaction of the longer alkyl chain with the strongly H-abstracting CS group was not observed in the S2 states of II compared with I, and this lack of effect was confirmed by showing that the excited state lifetimes were unaffected by a 40-fold change in the viscosity of the perfluoroalkane solvents. By contrast, a significantly shorter lifetime of the triplet state of II compared with I suggests that intramolecular interaction beween the hydrocarbon tail of II and the excited CS group may induce non-radiative relaxation in the longer-lived triplets.

ADDITIONS AND CORRECTIONS/AJOUTS ET CORRECTIONSAdditions and corrections: Solution multinuclear (31P,111Cd,77Se) magnetic resonance studies of cadmium complexes of heterocyclic aromatic thiones and the structure of [tetrakis(2(1H)-pyridinethione)cadmium] nitrate, [Cd(C5H5NS)4](NO3)2

<b>ADDITIONS AND CORRECTIONS/AJOUTS ET CORRECTIONS</b>Additions and corrections: Solution multinuclear (³¹P,¹¹¹Cd,⁷⁷Se) magnetic resonance studies of cadmium complexes of heterocyclic aromatic thiones and the structure of [tetrakis(2(1<i>H</i>)-pyridinethione)cadmium] nitrate, [Cd(C₅H₅NS)₄](NO₃)₂

Reactions of Thioketones with a Fluorinated ThioneS-Imide

N-(1-Adamantyl)hexafluorothioacetone S-imide (1) reacts readily with aromatic thioketones 4a−e to afford 1,4,2-dithiazolidines 5a−e as products of [3 + 2] dipolar cycloadditions. Unexpectedly, cycloadducts 5d and 5e, obtained from thioxanthione (4d) and 4,4′-(dimethoxy)thiobenzophenone (4e), respectively, are found to decompose at room temperature and could not be isolated as pure compounds. Unlike aromatic thiones, adamantanethione (4f) did not react with 1 at ambient temperature. However, reaction did occur upon heating in a sealed tube, and the new 1,4,2-dithiazolidine 9, bearing two adamantyl moieties, was isolated as the major product. The structure of 9 has been determined by X-ray diffraction analysis. The connectivity of the heterocyclic ring in this product indicates that the mechanism of its formation must proceed by a different route involving another in situ generated sulfur-centered 1,3-dipole. Retrocycloaddition of the primary adamantanethione cycloadduct 13 liberates hexafluorothioacetone, which is subsequently captured by S-imide 1 to give tetrakis(trifluoromethyl)-1,4,2-dithiazolidine 8 as a crystalline product. The structure of 8 has also been confirmed by X-ray diffraction analysis.

S2–S0Spectra of Jet-Cooled Xanthione and Benzopyranthione: Microscopic Solvation by Rare Gases

The laser-inducedS2–S0fluorescence excitation and dispersed emission spectra of two aromatic thiones, xanthione (XT) and benzopyranthione (BPT), have been measured under jet-cooled conditions. These emission spectra, together with the corresponding FT-IR and FT-Raman spectra andab initioCEP-31G calculations, have been used to achieve a complete vibrational analysis of BPT in its ground state, complementing that of XT, previously published. The 1:1 and 1:2 van der Waals complexes of XT and BPT with He, Ne, Ar, Kr, and Xe have been synthesized and characterized using their microscopic solvation shifts and the frequencies of their intermolecular (van der Waals) vibrations. In all cases the adatom preferentially occupies a position over the pyranthione ring in the 1:1 complex, and the 1:2 complex has a symmetrical sandwich (1|1) structure. No (2|0) isomer is observed. An analysis of the microscopic solvent shifts of the origin bands of the complexes indicates that dipole-induced dipole interactions contribute significantly to the binding energies. The binding energies and geometries of the 1:1 and 1:2 van der Waals complexes of XT, BPT, and pyranthione (PT) have been calculated using pairwise atom-atom Lennard–Jones 6–12 potentials and are consistent with the structures derived from experiment. The out-of-plane intermolecular stretching vibrations can be clearly observed in the excitation spectra of most complexes, and their assignments have been confirmed using model vibrational potentials.Ab initioSCF calculations including second order Møller–Plesset correlation are also reported for the PT·rare gas systems, and show nice agreement with the Lennard–Jones calculations and experiment.

Subpicosecond population decay time of the first excited singlet state of thioxanthione in fluid solution

The population decay time of the first excited singlet state of an aromatic thione, thioxanthione, has been measured for the first time in fluid solution at room temperature, using a laser pump-probe method. The average value of τ(S1) is 0.53±0.12 ps in three solvents, acetonitrile, acetone and 1-octanol giving a nonradiative S1 decay constant of (1.9 ± 0.4) × 1012 s−1. Using these data and a calculated value of the radiative lifetime of S1, a quantum yield of S1 → S0 fluorescence, φf < 5 × 10−8, is estimated, a value which is consistent with the failure to observe prompt fluorescence in these compounds. The short S1 lifetime of thioxanthione is attributed to fast S1(1A2)−Tn(3A1) intersystem crossing, which can occur by a first order spin-orbit coupling mechanism because Tn(3A1) (n = 1 or 2) has a lower energy than S1(1A2) in the polar solvents employed.

Spectral and Photophysical Properties of Aromatic Thiones in Micellar Systems: Xanthione as Convenient Absorption and Emission Probes

Spectral and photophysical properties of xanthione and pyranthione in micellar systems (SDS, CTAB, SPFO) have been studied and compared to their properties in polar and nonpolar solvents. It has been proved that xanthione, characterized by a very rich absorption and emission spectra, covering the range from 200 to 900 nm, related to its electronic states (T1(n, π*),T2(π, π*),S1(n, π*),S2(π, π*),S3(π, π*)) and showing, moreover, high sensitivity to environmental conditions makes a very convenient absorption and emission probe for investigation of the structure and properties of micellar systems.

Bildung von 1,2,4‐Trithiolanen in Dreikomponenten‐Gemischen aus Phenyl‐azid, aromatischen Thioketonen und 2,2,4,4‐Tetramethylcyclobutanthionen: Eine Schwefel‐Transfer‐Reaktion unter Bildung von ‘Thiocarbonylthiolaten’ ((Alkylidensulfonio)thiolaten) als reaktive Zwischenstufen

Formation of 1,2,4‐Trithiolanes in Three‐Component Reactions of Phenyl Azide, Aromatic Thiones, and 2,2,4,4‐Tetramethylcyclobutanethiones: A Sulfur‐Transfer Reaction to ‘Thiocarbonyl‐thiolates’ ((Alkylidenesulfonio)‐thiolates) as Reactive IntermediatesThe reaction of PhN3 and aromatic thioketones 18 (two‐component reaction) at 80° yields only the corresponding imines 22, S, and N2. Under similar conditions, in the presence of sterically crowded 2,2,4,4‐tetramethyl‐cyclobutanethiones 19 (three‐component reaction), 1,2,4‐trithiolanes of type 20 are formed in good yields in addition to imines 22 (Scheme 4). In case of 19a and 19c (X = CO, CS), the symmetrical trithiolanes 21a and 21b, respectively, are also isolated. With 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazole‐5(4H)‐thione (24) instead of aromatic thioketone 18, imine 25, trithiolane 21a, and 1,4,2‐dithiazolidine 26 are formed (Scheme 5). A reaction mechanism for the formation of 1,2,4‐trithiolanes 20 and 21, including an S‐transfer to generate ‘thiocarbonyl‐thiolates’ 2b and/or 2c and 1,3‐dipolar cycloaddition with a thioketone, is proposed in Scheme 7.

Sulfur Transfer in A Three-Component System Including Phenyl Azide, Aromatic Thione and Sterically Crowded Tetramethylcyclobutanethione

Abstract A new access to thiosulfines generated in a reaction system containing thiocarbonyl compounds and phenyl azide is described.

Sulfur Transfer in a Three-Component System Including Phenyl Azide, Aromatic Thione and Sterically Crowded Tetramethylcyclobutanethione

Abstract A new access to thiosulfines generated in a reaction system containing thiocarbonyl compounds and phenyl azide is described.

ChemInform Abstract: Vibrational Activation in the Radiationless Decay of the S2, S1, T1, and T2 States of Aromatic Thiones in Solution: Red Edge Effects

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Vibrational activation in the radiationless decay of the S2, S1, T1, and T2 states of aromatic thiones in solution: red edge effects

The quantum yields of phosphorescence, {Phi}{sub p}, of six aromatic thiones (xanthione, xanthione-d{sub 6}, benzopyranthione, pyranthione, tetramethylindanethione, and 4-bromotetramethylindanethione) have been measured accurately as a function of excitation wavelength and temperature in two solvents (3-methylpentane and perfluoro-1,3-dimethylcyclohexane). The values of {Phi}{sub p} decrease on the red edge of the S{sub 2} {l_arrow} S{sub 0} absorption band, particularly for pyranthione which has the shortest S{sub 2} lifetime. This red edge effect is attributed to competition between fast S{sub 2}{sup nu =0} {r_arrow}S{sub 0} and the finite rate of vibrational activation required before S{sub 2} can decay nonradiatively via S{sub 2}{sup {upsilon}} {r_arrow} S{sub 1}{sup nu}. The quantum yield of phosphorescene gradually increases with increasing excitation wavelength over the S{sub 1} {l_arrow} S{sub 0} absorption region as the fraction of triplet formed directly by excitation in the underlying T{sub 1} {l_arrow} S{sub 0} system increases. Excitation on the red edge of the T{sub 1} {l_arrow}S{sub 0} absorption results in a dramatic increase in {Phi}{sub p}. This second red edge effect is interpreted in terms of the nonequilibrium dynamic behavior of the coupled T{sub 1}-S{sub 1}-T{sub 2} system. Finite triplet sublevel spin depolarization rates may play an important role in determining the differencemore » in the dynamics of the system when excited initially to T{sub 1} compared with S{sub 1}. 52 refs., 10 figs., 1 tab.« less

Photochemistry of aromatic thiones in their S2 and T1 states. Role of triplet self-quenching and excimer formation

The quantum yields of photodecomposition of xanthione (XT), 4H- 1-benzopyran-4-thione (BPT) and 4H-pyran-4-thione (PT) subsequent to excitation to their S2 and S1 states have been measured as a function of thione concentration in inert perfluoroalkane solvents. The quantum yields of intramolecular photodecomposition of these thiones in S2 are immeasurably small. Intermolecular processes dominate the photochemical removal of the triplet states even at very low ( < 10–5 mol dm–3) thione concentrations. In inert perfluoroalkane solvents a photochemical channel in the diffusion-controlled triplet self-quenching process is responsible for the removal of the thione. A mechanism involving the intermediacy of triplet excimers is proposed.

Concerning apparent intersystem crossing efficiencies in molecules with small S 1T 1 energy gaps

Accurate values of the apparent quantum yields φ ST of S 1 ⇝ T 1 intersystem crossing were determined for several aromatic thiones in fluid solutions at room temperature. All values of φ ST are significantly less than unity at 295 K; this can be compared with a value of unity based on limited data previously obtained at 77 K, which has been assumed to hold at room temperature. The importance of triplet decay via back intersystem crossing to S 1 followed by radiative and non-radiative decay to S 0 is assessed. The possible involvement of T 2 in the subpicosecond decay of vibrationally excited S 1 is discussed. The potential importance of back intersystem crossing in other molecules with small S 1T 1 gaps is briefly addressed.

ChemInform Abstract: Radiationless Decay of Aromatic Thiones in Solution Selectively Excited to Their S3, S2, S1, and T1 States

Etude du declin sans radiation de thiones aromatiques sous l'excitation selective de leurs etats singulets-1,2,3 et triplet 1

The role of T 1 self-quenching in photochemical decay of aromatic thiones

The photochemical properties of 4 H-1-benzopyran-4-thione (BPT) excited to the S 1 state have been studied for a thione concentration of 10 −6 – 10 −2 M. The measured quantum yield of photochemical decay of BPT is very small in unreactive perfluoro-1,3-dimethylcyclohexane φ BPT < 5 X 10 −4, and significantly higher in active 3-methylpentane φ BPT ≈ 10 −2. For thione concentrations of 10 −3 M or greater, the photochemical decay has been proved to occur not directly from the T 1 state but through the T 1 self-quenching processes. Although the main mechanism of the process is T 1 + S 0 → 2S 0, our experimental results can be explained only on the basis of the formation of the photochemically reactive T 1 excimer.