Laser-Induced Fluorescence of Decamethylrhenocene in Low-Temperature Matrices

Abstract

The emission and excitation spectra of decamethylrhenocene, Re(η 5 -C 5 Me 5 ) 2 have been recorded in argon and in nitrogen matrices with a tunable pulsed laser as exciting source. In argon matrices two sets of spectra may be excited selectively corresponding to different trapping sites or conformers of the guest molecules. Each set is dominated by a progression in ν 8 , a vibration corresponding to the in-phase combination of ringmetal-ring and ring-methyl bending modes (ν 8 ′ ) 392 (2) cm -1 ν 8 ′′ ) 383 (1) cm -1 ). Much weaker features can be detected corresponding to progressions involving the three other totally symmetric modes (ν x + nν 8 , x ) 6, 7, 9, n ) 0, 1, 2, ...). The emission and excitation bands in the principal site are symmetrical in shape with full width at half-maximum of only ca. 6 cm -1 . The spectra of Re(η 5 -C 5 Me 5 ) 2 in nitrogen matrices are similar to those in argon matrices, but differ in site/conformer structure. The excited state lifetime in nitrogen matrices has been determined by single photon counting methods to be 3.69 (7) ns. The quantum yield for emission in nitrogen matrices is estimated as 0.010.

Electronic Structure and Photophysics of Low Spin d5 Metallocenes

“…Upon irradiation of ReCp* 2 in toluene at 568 nm, broad emission is observed at room temperature (λ max,em = 641 nm), consistent with previous low temperature photoluminescence measurements (Figure 6). 20,60,61 Monitoring the emission of this compound at 641 nm reveals a room temperature lifetime of 1.8 ns in pentane, compared to 3.69 ns in a N 2 matrix at 12 K. 60 This lifetime, together with the almost perfect overlap of the (0, 0) component in absorption and emission in a low temperature matrix, is consistent with fluorescence from a 2 LMCT excited state. 20 By contrast, no emission is detected for MnCp* 2 .…”