Solvent Effects on the Spectroscopic and Photophysical Properties of thetrans-(1,4,8,11-Tetraazacyclotetradecane)diisothiocyanatochromium(III) Ion,trans-[Cr(cyclam)(NCS)₂]⁺

Abstract

The spectroscopy and photophysics of trans-[Cr(cyclam)(NCS)2]+ (where cyclam is 1,4,8,11-tetraazacyclotetradecane) were studied in a range of solvents. The cyclam NH stretching vibration [nu(NH)] wavenumber correlates with the Gutmann donor number, whereas the thiocyanate CN stretching vibration [nu(CN)] wavenumber correlates with the Snyder solvent strength (P') scale. These results signify that there is a difference in the solvent interactions with the two types of ligands. The energy of the ligand-to-metal charge transfer absorption maximum between 310 and 320 nm and the energy of the spin-forbidden (doublet-quartet) absorption and emission bands above 700 nm correlate with the nu(CN) wavenumber. This establishes the dominant role of solvent effects at the NCS- ligand in "tuning" the energy of these spectroscopic features. Quantum yields phirx for photosubstitution are <0.02 at 54 degrees C and <0.002 at 22 degrees C, demonstrating that photochemical reaction is a very minor pathway. The effects of solvent and temperature on the nonradiative decay of the doublet excited-state were investigated by observing the time-resolved phosphorescence between 700 and 750 nm. Below 30 degrees C, the lifetimes are relatively temperature-independent, whereas at higher temperatures, a strong Arrhenius-type dependence is observed. Values for the preexponential factor (A) and the activation energy (Ea) are solvent-dependent and follow a Barclay-Butler-type correlation. These observations are consistent with a dominant back-intersystem crossing pathway for nonradiative decay in the higher-temperature region. From trends observed between ln(A) and the nu(CN) frequency, it appears that solvent effects at the thiocyanate ligand play a dominant role in influencing the rate of nonradiative decay in the high-temperature region.

Fabrication of Perovskite Films with Large Columnar Grains via Solvent-Mediated Ostwald Ripening for Efficient Inverted Perovskite Solar Cells

“…In order to observe more clearly the evolution of the grain size during annealing, we also prepare perovskite precursor films by introducing optimized DMSO into PbI 2 /DMF solution . Because DMSO has a stronger Lewis basicity , and a higher boiling point than DMF, the function of Ostwald ripening in controlling the grain size is obvious (see Figure d–f). These results reconfirm the key roles of the residual solvent in meditating the Ostwald ripening process.…”

Catalysis direction selective asymmetric polymerization in chiral liquid crystal medium

“…270 nm) in THF, and chloroform solutions, while that is opposite in the case of DMF and DMSO solutions. The polarity of the solvents increases in the order of THF, chloroform, DMF, Iseki, T; Kawabata, K; Kawashima, H; Goto, H.*, Catalysis direction selective asymmetric polymerization in chiral liquid crystal medium, Polymer, 55(1), 66-72 (2014) and DMSO [23,24]. The differences in the intensity of the Cotton effect in solution are due to conformational changes of poly-3r by changing solvents polarity.…”

Macrocyclic coordination chemistry

“…The bis(isothiocyanate) chromium(III) cyclam complex has been studied for solvent effects on spectroscopic and photophysical properties. 42 Different solvent interactions were observed with the two types of ligands via the cyclam NH or the isothiocyanate CN, with the solvent effects on the NCS group predominant.…”