No abstract

We characterized a series of dimethylamino-stilbene derivatives as standards for time-domain and frequency-domain lifetime measurements. The substances have reasonable quantum yields, are soluble in solvents available with a high purity, and do not show significant sensitivity to oxygen quenching. All the fluorophores displayed single exponential intensity decays, as characterized by frequency-domain measurements to 10 GHz. The decay times vary from 880 to 57 ps, depending on structure, solvent, and temperature, which is a useful range for modern picosecond time-domain or gigahertz frequency-domain instruments. These fluorophores may be used either to test an instrument or as reference compounds to eliminate color effects. We also characterized two-fluorophore mixtures, with the decay times spaced twofold (150 and 300 ps), with varying proportions. These mixtures are useful for testing the resolution of other time- and frequency-domain instrumentation. The excitation wavelength ranges from 260 to 430 nm, and the emission from 350 to 550 nm. The decay times are independent of the excitation and emission wavelengths.

The electric dipole moment in the ground (μg) and in the first excited singlet state (μe) of co-substituted acceptors in 4-dimethylamino-trans-styrenes (Z = P(S)Ph2 , P(O)Ph2 , SO2CH3 ) were determined by solvatochromic and thermochromic methods. The obtained values of μe and μg and the values for Z = CN and Z = NO 2 known from the literature [2] fulfill the linear relation between the dipole moments (μe or μg and the Hammett constants σp of the substituents. On pincreasing the electron-acceptor power of Z, μe grows faster than μg

Preparation of β‐Substituted trans‐Ethylene Diphenylphosphines and Sulphides by P(0) and P(S)‐activated Olefination Methylene bis‐diphenylphosphine monoxide (3c) in tuluene reacts regiospecifically and stereoselectively with aldehydes in the presence of potassium tert‐butoxide to ß‐substituted transethylene diphenylphosphines 6, which can be oxidized to the sulphides 2 by sulphur in acetone. These sulphides 2 are to be obtained also directly from methylene bis‐diphenylphosphine oxide sulphide 3b and methylene bis‐diphenylphosphine disulphide 3d, respectively, under the same olefination conditions. But the yields are smaller and the purification of the raw products is much more difficult, if 3d is used.

Methan‐bis‐(phosphonsäure‐diäthylester) reagiert mit Aldehyden in Gegenwart der äquimolaren Menge Kalium‐tert.‐butylat zu 2‐substituierten Äthylen‐1‐phosphonsäure‐diäthylestern in präparativem Maßstab. Durch Analyse der Signalfolge für die Vinylprotonen im 1H‐NMR‐Spektrum wird die trans‐Konfiguration der isolierten Äthylen‐phosphonsäure‐ester sichergestellt. Für die Selektion cis‐ oder trans‐Konfiguration der Reaktionsprodukte wird eine sterische Hinderung im Übergangszustand des zweiten Reaktionsschrittes als entscheidend angesehen.