TY - JOUR
T1 - Temporal behavior of the singlet molecular oxygen emission in imidazolium and morpholinium ionic liquids and its implications
AU - Yoshida, Tsuyoshi
AU - Kawai, Akio
AU - Khara, Dinesh Chandra
AU - Samanta, Anunay
N1 - Publisher Copyright:
© 2015 American Chemical Society.
PY - 2015/6/4
Y1 - 2015/6/4
N2 - The solvent effect of ionic liquids on the lifetime of singlet molecular oxygen, O2(1Δg), was investigated by means of time-resolved near-IR emission spectroscopy. O2(1Δg) was generated by photosensitization of methylene blue in morpholinium and imidazolium ionic liquids, both comprising various alkyl chains of different lengths. The measured time profiles of O2(1Δg) luminescence for the 1Δg 3∑g- transition were represented by a single-exponential decay function. The phosphorescence lifetime was found to be correlated with the alkyl chain length of the morpholinium ionic liquids. This observation was interpreted by considering efficient quenching of O2(1Δg) through energy transfer to the high-frequency C-H stretching modes of the N-alkyl chain in the morpholinium cation. Interestingly, we found that O2(1Δg) quenching by the C-H stretching modes of the ring of the cations was remarkably depressed. The kinetics of the O2(1Δg) emission decay process was discussed on the basis of the heterogeneous structure of ionic liquids consisting of polar and nonpolar domains.
AB - The solvent effect of ionic liquids on the lifetime of singlet molecular oxygen, O2(1Δg), was investigated by means of time-resolved near-IR emission spectroscopy. O2(1Δg) was generated by photosensitization of methylene blue in morpholinium and imidazolium ionic liquids, both comprising various alkyl chains of different lengths. The measured time profiles of O2(1Δg) luminescence for the 1Δg 3∑g- transition were represented by a single-exponential decay function. The phosphorescence lifetime was found to be correlated with the alkyl chain length of the morpholinium ionic liquids. This observation was interpreted by considering efficient quenching of O2(1Δg) through energy transfer to the high-frequency C-H stretching modes of the N-alkyl chain in the morpholinium cation. Interestingly, we found that O2(1Δg) quenching by the C-H stretching modes of the ring of the cations was remarkably depressed. The kinetics of the O2(1Δg) emission decay process was discussed on the basis of the heterogeneous structure of ionic liquids consisting of polar and nonpolar domains.
UR - http://www.scopus.com/inward/record.url?scp=84930934544&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcb.5b01996
DO - 10.1021/acs.jpcb.5b01996
M3 - Article
AN - SCOPUS:84930934544
SN - 1520-6106
VL - 119
SP - 6696
EP - 6702
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 22
ER -