Pressure-induced tuning of fluorescence to phosphorescence in [Cr(urea- h4) 6] (ClO 4) 3 and [Cr(urea- d4) 6] (ClO 4) 3

• Published in: Chemical physics letters Vol. 199; no. 1; pp. 1 - 9
• Main Authors: Yersin, Hartmut, Huber, Peter, Gietl, Gerhard, Trümbach, Dietrich
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30.10.1992; Elsevier Science
• Subjects: Atomic and molecular physics; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Molecular properties and interactions with photons; Physics; Cationic complex; Satellite line; Organic ligand; Fluorescence; Chlorates; Transition metal Complexes; Experimental study; Spectral line shift; Pressure; Single crystal; Inorganic compound; Urea; Chromium Complexes; Ultraviolet spectrum; Potential surface; Vibronic transition; Phosphorescence; Infrared spectrum; Vibrational mode; Low temperature
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/0009-2614(92)80040-I

In [Cr(urea- h 4) 6] (ClO 4) 3 the lowest sublevel of 4T 2g (t 2 2ge 1 g) lies Δ E = 90 ± 10 cm −1 above the lower 2E g(t 3 2g) sublevel. At 1.3 K one observes a fine-structured phosphorescence. With temperature increase, for example to 120 K, the quartet is thermally occupied and one obtains a broad-band fluorescence. Pressure application at the same temperature results in a blue-shift of 4T 2g relative to 2E g. This reduces the thermal repopulation of the quartet. Thus it is possible to induce a fine-structured phosphorescence by pressure. The emission intensity of the origin(s) corresponding to 2E g increases by a factor of about 10 2 with pressure application up to 20 kbar. [Cr(urea- d 4) 6] (ClO 4) 3 exhibits somewhat different properties. Δ E is larger (140 ± 10 cm −1) and the observed effects are less distinct. The origin lines corresponding to 2E g exhibit linear shifts of Δ ν /Δ p = −(5.5 ± 0.5) cm −1/kbar (protonated compound) and Δ ν /Δ p = −(5.3 ± 0.5) cm −1/kbar (deuterated compound). Vibrational frequencies, determined from vibronic satellites and IR spectra, are given for both compounds. Most vibronic satellites in the phosphorescence spectra are blue-shifted with pressure relative to the origins.