Synthesis, structure, complexation, and luminescence properties of the first metal-organic curcumin compound Bis(4-triphenylsiloxy)curcumin

Abstract The synthesis and structural characterization of 1,7-bis(4-triphenylsiloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione ( 1  = Ph 3 SiCurcH) and 1,7-bis(4-methoxycarbonyloxy-3-methoxy-phenyl)-1,6-heptadiene-3,5-dione ( 2  = MeOC(O)CurcH) are reported. Compound 1 represents the first metal-organic curcumin derivative. The complexation of 1 and 2 with Cu 2+ has been studied. The new copper(II) complexes (Ph 3 SiCurc) 2 Cu ( 3 ) and [MeOC(O)Curc] 2 Cu·4MeCN ( 4 ) have been prepared and their crystal structures determined by single crystal X-ray diffraction. Moreover, the optical properties of the solid compound 1 have been investigated in detail. The emission spectrum shows a vibronic fine structure that has been analysed in terms of Franck-Condon factors. The excitation spectrum is broad and structureless and may be interpreted in terms of an interband transition as is also confirmed by diffuse reflectance spectra. Due to the weak intermolecular interactions, an isolated-molecule model is used instead for the assignment of the transitions, which are thus characterized as S 1 ↔ S 0 or π * ↔ π fluorescent transitions. Despite the electric-dipole allowed nature of the transition, the quantum yield is Φ = (2.4 ± 0.3)% in agreement with other findings on curcumin derivatives.