Photochemistry and photophysics of aqueous cyanopentaamminechromium(2+) and trans-dicyanotetraamminechromium(1+)

Photochemistry and Photophysics of Chromium(III) Complexes

“…23 The linearity of the plot for many complexes implies that relaxation is dominated by a single process, and some of these show evidence 175 of isokinetic behavior with Barclay-Butler plots for data derived from different solvent media. Similar observations stimulated 95,176 a set of "emission rules" based on the high-temperature deactivation process being direct doublet reaction. These rules suggested (i) a positive correlation between the doublet lifetime of a CrL 6 n+ complex and the ligand-field strength of L and (ii) that relatively short lifetimes would be observed for mixed-ligand complexes when the ligand that is labilized in the ground-state thermal reaction is located on the weakest-field axis.…”

“…From conductivity monitoring experiments, 124,125,156,157 it is 0.68 for Cr(en) 3 3+ , in excellent agreement with the values from the direct methods. These studies also gave 157 the values 0.74 for Cr(NH 3 ) 5 (CN) 2+ in agreement with the 0.73 value 95 from quenching experiments, 0.77 for Cr(NH 3 ) 5 -(NCS) 2+ , 1.0 for trans-Cr(en) 2 F 2 + , and >0. 93 for Cr(bpy) 3 3+ .…”

“…Looked at from the other direction, the success of the model supports the assumption of quartet reaction and, by extension, the BISC pathway of doublet reaction for those complexes which show the same stereochemistry for the quenchable and unquenchable photochemistry, such as 64 Cr(en) 3 3+ and Cr-(NH 3 ) 5 CN 2+ . 95 There is no reason to attribute analogous stereochemical features to the proposed alternatives of a direct reaction from the doublet state or via a GSI formed by tunneling to the ground state. For the direct doublet reaction, the expectation is that the substitution reactions would mimic those of the ground state, which are strongly stereoretentive.…”

“…88 Some parallels with this behavior can be found in mixed cyanoam(m)ine complexes. Cyano complexes have been extensively studied [90][91][92][93][94][95][96][97][98][99][100] by the Perugia group of Riccieri and Zinato and co-workers. Zinato has written an excellent review 24 of their synthesis, properties, spectroscopy, thermal kinetics, photochemistry, and photophysics.…”

Metal centered ligand field excited states: Their roles in the design and performance of transition metal based photochemical molecular devices

“…Additional evidence for this mechanism is found in those cases where the substitution patterns for the quenchable (doublet channel) and unquenchable (prompt quartet channel) portions of the photochemistry are similar (e.g. Cr(en) 3 3+ and Cr(NH 3 ) 5 CN 2+ ) [42,[103][104][105]. There are a few cases for which little to no reaction quenching is detected under conditions of total phosphorescence quenching, namely, for Cr(CN) 5 X n− complexes [91,[106][107][108].…”