Effects of solvent, temperature, and pressure on the photophysical and visible-spectroscopic behavior of the trans-diammine(1,4,8,11-tetraazacyclotetradecane)chromium(III) ion

Metal-to-Ligand Charge Transfer Excited-State ν(CO) Shifts in Rigid Media

“…The orbital energy difference, ∆E, is related to E 0 and the pairing energy, P, by E 0 ) ∆E -P. The increase in π*(4,4′-X 2 bpy) decreases the π*(4,4′-X 2 bpy •-)-π*(CO) energy gap, which enhances π*(4,4′-X 2 bpy •-)-π*(CO) mixing and decreases ν j es . 16,17,22,51 By inference, the rigid medium effect has the same origin. The loss of orientational polarization increases the energy of π*(4,4′-X 2 bpy) leading to enhanced π*-π* mixing.…”

“…The increases in emission energy (E em ) and energy gap (E 0 ) between fluid and rigid media are well documented for MLCT excited states. [14][15][16][17][18][19][20][21][22][23][24] They are caused by the frozen character of the orientational part of the solvent dielectric. Except for very shortlived excited states, emission in fluid solution occurs with the full dielectric polarization equilibrated with the electronic configuration of the excited state.…”

“…However, for MLCT excited states, the difference between frozen and fluid media can be large (Table 2 and On the basis of the similarity in MLCT absorption band energies for [Ru(bpy) 3 ] 2+ and related complexes in CH 3 CN and PMMA, the frozen dielectric properties of the two are comparable. [15][16][17]22,51,52 Absorption is an instantaneous process on the time scale for nuclear motions, whether in solution or a rigid medium, and E abs (fr) -E abs (fl) ∼ 0. E abs (fr) and E abs (fl) are the absorption band energies in rigid and fluid media, respectively.…”

“…[14][15][16][17][18][19][20][21][22][23][24] They observed an increase in MLCT emission energy in rigid compared to fluid media. It has been shown that ligand-localized ππ* excited-state energies in related complexes are relatively unaffected by the transition from fluid to glass.…”

Photochemistry and Photophysics of Chromium(III) Complexes

“…cis- and trans- Cr(cyclam)(NH 3 ) 2 3+ differ markedly in their photochemical and photophysical properties. ,− The trans isomer is photoinert, although a photoredox process 200 with φ = 0.01 occurs in the presence of nitrate ion. In contrast, the cis isomer photoaquates ammonia with a quantum yield of 0.15 ± 0.05 independent of irradiation wavelength, including directly into the doublet state .…”