Synthese, Struktur und photophysikalische Eigenschaften von polyarylierten Imidazolen und Oxazolen

Abstract

Synthesis, Structure, and Photophysical Properties of Polyarylated Imidazoles and Oxazoles 23 tetraphenylimidazoles 1,2 and 11 triphenyloxazoles 4,5 with amino, nitro, methoxy, hydroxy, or halogeno substituents chiefly in the para position were prepared. The absorption and fluorescence emission properties were investigated in ethanolic solution. The effects of the substituents in 1,2 on the spectral shifts show that the arrangement of the phenyl rings in 1 position is not coplanar in relation to the heterocycle whereas the phenyl rings in 2 position are more coplanar. The spectral changes of compound 2a in solvents of various polarity (dielectric constants 2,02–47,24) are almost negligible. The Stokes shift is moderately increased. A remarkable increase in the fluorescence quantum yield is observed by chlorine substitution in phenyl ring 2.

2-Methyl-1,4,5-triphenyl-1H-imidazole

“…This relative conformation for the phenyl rings seems to minimize steric hindrance in the overall molecule. A similar non-conjugated arrangement was previously observed for a symmetrically tetrasubstituted imidazole (Buttke et al, 1997). In this case, the substituents on N1, C2, C4 and C5 were 4-methoxyphenyl groups, and the calculated dihedral angles between the phenyl moieties and the imidazole ring were 105.9 (substituent on N1), 15.1 (substituent on C2), 47.9 (substituent on C4) and 101.9 (substituent on C5).…”

Cyclization of Propargylic Amides: Mild Access to Oxazole Derivatives

“…For the substrates containing only one propargylic amide side chain, all substrates underwent a smooth reaction to furnish tert-butyl-(2 a), benzyl-(2 b), thiophenyl-substituted oxazoles 2 c (Table 1, entries 1-3) as well as the bulky anthracenylsubstituted oxazole 2 d (Table 1, entry 4) and the biphenyl substrate 2 e, most of them in excellent yields. Concerning the interesting optical abilities of aryl-substituted oxazoles and their application as luminophores, [13] we investigated the reactions of substrates containing up to three proA C H T U N G T R E N N U N G pargylic moieties in one molecule. To our delight, most of these substrates showed full conversion to the corresponding oxazoles (Table 1, entries 6, 7, 9) for the bifunctionalized, and even substrate 1 k (Table 1, entry 11), which contains three propargylic moieties, delivered 2 k as a single product in a remarkable yield of 86 %.…”

“…. a)13 C{ 1 H} NMR spectrum, b) DEPT 135 NMR spectrum, and c) DEPT 90 NMR spectrum. All spectra were taken during the conversion of 1 l with 5.0 mol % AuCl 3 at À20 8C.…”

Bright, emission tunable fluorescent dyes based on imidazole and π-expanded imidazole

“…Interestingly the effect of the NMe 2 group at position 2 of the phenyl ring is different than for an analogous tetraphenylimidazole possessing a 4-N,N-dimethylaminophenyl substituent f fl ¼ 0.31. 38 Although f fl of compound 22 is almost the same (0.28) in comparison with View Online imidazole bearing 4-N,N-dimethylaminophenyl group, the fluorescence maximum is strongly red shifted and the absorption maximum is strongly blue shifted. As a result the Stokes shift is significantly higher ($16 000 cm À1 vs. 8500 cm À1 ).…”