Phenyl substitution as an effective way to control the luminescent properties of polyphenylcyclopentadienyl lanthanide complexes

Lanthanide complexes $\mathrm{[Cp^{X}LnCl_2(Me_3{tach})]_n}$ ($\mathrm{Ln}$ = $\mathrm{Tb}$, $\mathrm{Gd}$; $\mathrm{Cp^X}$ = $\mathrm{Cp}$, $\mathrm{Cp^{Ph_4}}$; $\mathrm{Me_3tach}$ = 1,3,5-trimethyl-1,3,5-triazacyclohexane; $n = 1, 2$), containing cyclopentadienyl ($\mathrm{Cp}$), 1,3-diphenylcyclopentadienyl ($\mathrm{Cp^{Ph_2}}$) and tetraphenyl-cyclopentadienyl ($\mathrm{Cp^{Ph_4}}$) anions as $\pi$-bonded antenna ligands, have been synthesized. A combined analysis of quantum chemical, optical and X-ray diffraction data has shown that the introduction of phenyl groups into the Cp ring leads to the inevitable appearance of intraligand charge transfer states due to the nonequivalence of the phenyl rings.