Simple correlation between the main luminescence parameters of the metallocene complex in the liquid phase

Abstract

Metallocene complexes of Group 4B metals possess rather uncommon phosphorescent states1—5 appearing due to the ligand to metal charge transfer (LMCT).1—12 The luminescence quantum yields (ΦL) and lifetimes of elec tronically excited states (τ) of metallocenes of the tita nium subgroup are among highest and longest ones for the known LMCT states and other radiative states (T→S0) of coordination compounds. In the present work, we stud ied the lifetimes of the LMCT excited states of metallocene rac C6H10(IndH4)2ZrCl2 (1) 13 (Ind is indenyl) in solu tions. This metallocene intensely luminesces in the liquid state at room temperature. The proportional dependence ΦL ∝ τ of the radiative characteristics of compound 1 was observed in solvents of different solvating ability. Solutions prepared from single crystals of com pound 1 were studied. All solvents were subjected to spe cial repetitive purification from traces of admixtures, oxy gen, and moisture using freezing—thawing out cycles in a high vacuum line according to known procedures.1—4 The concentration of the complex in solutions was 3•10–5—2•10–4 mol L–1. The lifetimes were determined upon the excitation of solutions of metallocene 1 by a photodiode laser with λexc = 375 nm on a Fluotime 200 fluorimeter (PicoQuant GmbH, Germany) using the pho ton counting method and the commercial FluoFit pro gram package. The luminescence quantum yields of solu tions of compound 1 were determined by a comparison of the integral luminescence intensities of the sample (Dx) and standard solution (Dst) with a correction for the dif ference of the refractive coefficients of the solvent in the sample (nx) and in the standard (nst) using the known formula