trans-4-Stilbenecarboxylatoalkylpentaamminecobalt(III) Perchlorates: Synthesis and Intramolecular Energy Transfer

Abstract

Three homologs of trans-4-stilbenecarboxylic acid, viz., trans-4-stilbeneacetic acid (18), β-(trans-4-stilbene)propionic acid (19), and γ-(trans-4-stilbene)butyric acid (20) were synthesized and, together with the parent trans-4-stilbenecarboxylic acid, used to obtain the corresponding [ω-(trans-4-stilbene)carboxylatoalkylpentaamminecobalt(III) complexes, [(PhCH=CHC6H4(CH2)nCOO)Co(NH3)5]2+ (1-4), where n = 0, 1, 2, or 3. Fluorescence studies suggest that an intramolecular excitation energy transfer occurs from the first excited singlet state of the ligand to the metal giving rise to a charge-transfer triplet-excited state of the complex, based on the analogy with previous work on complex 1. The efficiency of the energy transfer seems to decrease with increasing number of the methylene groups in the ligand.