Photoexcitation dynamics of p-nitroaniline and N,N-dimethyl-p-nitroaniline in 1-alkyl-3-methylimidazolium-cation based ionic liquids with different alkyl-chain lengthsElectronic supplementary information (ESI) available: Tables of the parameters obtained by the fit of the time profiles of the transient absorption at different wavelengths in different ionic liquids, the table of parameters obtained by the spectral simulation of DMpNA, plots of the time profiles of the transient absorption at diff

• Main Authors: Kimura, Y, Ibaraki, S, Hirano, R, Sugita, Y, Yasaka, Y, Ueno, M
• Format: Journal Article
• Language: English
• Published: 23.08.2017
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp03610h

Photoexcitation dynamics of p -nitroaniline (pNA) and N , N -dimethyl- p -nitroaniline (DMpNA) in 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C n mim][NTf 2 ]) with different alkyl chain lengths (from C 2 to C 12 ) was investigated using transient absorption spectroscopy. The internal conversion rate from the excited state to the ground state was estimated from bleach recovery around the ground state absorption centre, and the successive vibrational cooling rate in the ground state was estimated from the decay of the hot band observed at the red-edge of ground state absorption. The internal conversion rate slightly decreased with an increase in the alkyl-chain length of the cation, while the dependence of DMpNA was more significant than that of pNA. The extent of change was correlated with the change of the reaction free energy and solvent reorganization energy estimated from the absorption spectrum assuming that the internal conversion process is modelled by a back-electron-transfer process. The vibrational cooling rate estimated from the decay of hot-band absorption slightly decreased with an increase in the alkyl-chain length of the cation for both solutes. The hot-band decay of pNA was about 1.5-times faster than that of DMpNA, irrespective of the alkyl-chain length. Back electron transfer and vibrational energy relaxation of p -nitroaniline and N,N -dimethyl- p -nitroaniline in ionic liquids were investigated using transient absorption spectroscopy.