Effect of conformation on the chemiluminescence efficiency of light-producing 2-methyl-6-(4-methoxy-phenyl)imidazo[1,2-α]pyrazin-3(7H)-ones

Analogues of the light-producing substrate 2-methyl-6-(4-methoxyphenyl)imidazo[1,2-alpha ]pyrazin-3(7H)-one, with restrictions on the dihedral angles between the pyrazine and the 4-methoxyphenyl rings, were synthesized. These compounds were used to investigate the effects of the conformation between the pyrazine and 4-methoxyphenyl rings on their chemiluminescence efficiencies in aqueous solutions. The effects of the conformation on the chemiluminescence efficiencies were clearly observed; the decrease of the dihedral angle caused a light-enhancing effect and, conversely, the increase of the angle dramatically decreased the chemiluminescence efficiency. These effects on the chemiluminescence efficiencies are attributed to the influence of the conformation on the fluorescence efficiency of the emitter. Copyright (C) 2001 John Wiley & Sons, Ltd.