Triplet states in 1,3-butadiene

The electron impact excitation spectrum 0f 1,3-butadiene has been studied at 20, 35 and 55 eV impact energies and scattering angles of 10° to 80°. Two low lying states are observed with maxima at 3.2 and 4.9 eV, and are identified as the ³B_u state and ³A_g state respectively     

Triplet photophysics of gold(III) porphyrins

Gold porphyrins are often used as electron-accepting chromophores in donor-acceptor complexes for the study of photoinduced electron transfer, and they can also be involved in triplet-triplet energy-transfer interactions with other chromophores. Since the lowest excited singlet state is very short-lived (240 fs), the triplet state is usually the starting point for the transfer reactions, and it is therefore crucial to understand its photophysics. The triplet state of various gold porphyrins has been reported to have a lifetime of around 1.5 ns at room temperature and to have a biexponential decay both in emission and in transient absorption with decay times of around 10 and 100 micros at 80 K. In this paper, the triplet photophysics of two gold porphyrins (Au(III) 5,15-bis(3,5-di-tert-butylphenyl)-2,8,12,18-tetraethyl-3,7,13,17-tetramethylporphyrin and Au(III) 5,10,15,20-tetra(3,5-di-tert-butylphenyl)porphyrin) are studied by steady-state and time-resolved absorption and emission spectroscopy over a wide temperature range (4-300 K). The study reveals the existence of a dark state with an approximate lifetime of 50 ns, which was not previously observed. This state acts as an intermediate between the short-lived singlet and the triplet state manifold. In addition, we present DFT calculations, in which the core electrons of the central metal were replaced by a pseudopotential to account for the relativistic effects, which suggest that the lowest excited singlet state is an optically forbidden ligand-to-metal charge-transfer (LMCT) state. This LMCT state is an obvious candidate for the experimentally observed dark state, and it is shown to dictate the photophysical properties of gold porphyrins by acting as a gate for triplet state formation versus direct return to the ground state.     

Triplet diphenylcarbenes protected by (trimethylsilyl)ethynyl groups

(2,4,6-Tribromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1a) was shown to be stable enough to survive Sonogashira coupling reaction conditions at an elevated temperature and gave not only a para-monosubstituted product, (4-trimethylsilylethynyl-2,6-dibromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1b), but also a disubstituted one, [2,4-bis(trimethylsilylethynyl)-6-bromophenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1c), and a trisubstituted product, [2,4,6-tris(trimethylsilylethynyl)phenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1d). Triplet diphenylcarbenes (DPCs) generated by photolysis of those ethynylated diphenyldiazomethanes were characterized by ESR and UV-vis spectroscopies at low temperature and laser flash photolysis techniques in solution at room temperature. Although ESR data indicated that ethynyl groups at the ortho positions are likely to stabilize triplet DPCs both sterically and electronically more effectively than o-bromine groups, kinetic studies suggested that the stability of triplet DPCs is not increased by o-ethynyl groups, as opposed to o-bromine groups. It is likely that triplet DPCs decay by interacting with the o-ethynyl groups.     

1,3-Benzothiazines (review)

Data on the methods for the synthesis of 1,3-benzothiazines and their derivatives and their chemical properties and physiological activity are correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 291–308, April, 1979.     

Magnetomesogens: Bis(1,3-di(4'-decoxyphenyl)propane-1,3-dionato)oxovanadium (IV)

β-Diketonate complexes of oxovanadium (IV) have been synthesized and their mesomorphic behaviour investigated. The title complex exhibits a short range monotropic columnar discotic phase, identified by its optical texture and by miscibility studies. The optical texture of the phase is retained on cooling to the crystal. As a consequence of the unpaired electron on vanadium the complexes are paramagnetic.     

Synthesis of (1,3-adamantylene)bis-1,3-dicarbonyl compounds

Reactions of 1,3-dihydroxyadamantane with 1,3-dicarbonyl compounds in the presence of 5 mol % of In(OTf)₃ afforded a series of (1,3-adamantylene)bis-1,3-dicarbonyl compounds in yields of 25–83%.     

Silicon Tris(perchloro)dioxolene: A Neutral Triplet Diradical

The reaction of ortho‐quinones with silicon tetraiodide leads to neutral silicon trisdioxolenes in high yield, delivering the unknown oxidized form of triscatecholatosilicate dianions and the first example of open‐shell semiquinonates connected via a single non‐metal center. Silicon tris(perchloro)dioxolene is a stable diradical with a triplet ground state, as supported by X‐ray diffraction; IR, resonance Raman, UV/Vis, and (VT)EPR spectroscopy; and Kohn–Sham broken‐symmetry computations. Preliminary results suggest that the preferred magnetic ground state can be altered through variation of the substituents.     

Phosphorylated 1,3-diazoles (review)

The principal methods for obtaining and converting phosphorylated 1,3-diazoles, including³²P-labeled compounds and compounds that contain spin labels, and their use in organic synthesis, molecular biology, bioorganic chemistry, medicine, and agriculture are examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 723–740, June, 1990.