Synthesis and photophysical characterization of novel tri-(hetero)arylimidazoles

The imidazole nucleus is of great importance in medicinal chemistry because it plays an important role in biochemical processes as structural component of several biomolecules (for example, histidine, vitamin B12, nucleotides, histamine and biotin), and also has various pharmacological activities (anti-HIV, anti-convulsant, calcium antagonist, inhibitors of thromboxane A2 synthase, antihistaminic, anti-parkinsonism and MAO inhibitor).1             Besides their application in medicinal chemistry, 2,4,5-tri(hetero)aryl-imidazoles are also a versatile class of compounds in materials chemistry due to their optoelectronic properties. Earlier studies reported by us showed that the optical and thermal properties of these derivatives could be tuned by substitution of aryl groups at positions 2, 4 and 5 by 5-membered heterocycles giving rise to innovative applications of these p-conjugated systems in nonlinear optics (e.g. second harmonic generators (SHG)), chemosensors, OLEDs and DNA intercalators.2 In this communication, we describe the synthesis of new tri-(hetero)arylimidazoles, functionalized with different heterocycles, to evaluate the photophysical properties of the resulting compounds. The imidazole derivatives 2a-d were obtained in good yields by reaction of diphenylethanedione with an heterocyclic aldehyde 1a-d in the presence of ammonium acetate in acetic acid at reflux. The new derivatives were characterized by the usual techniques and a detailed photophysical study was undertaken.