TY - JOUR
T1 - Effect of the media on the quantum yield of singlet oxygen (O2(1Δg)) production by 9H-fluoren-9-one
T2 - Solvents and solvent mixtures
AU - Martinez, Claudia G.
AU - Neuner, Annette
AU - Martí, Cristina
AU - Nonell, Santi
AU - Braun, André M.
AU - Oliveros, Esther
PY - 2003
Y1 - 2003
N2 - We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1Δg), denoted as 1O2) by 9H-fluoren-9-one (FLU). The normalized empirical parameter ENT derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production ΦΔ decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (ΦISC). Values of ΦΔ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ΦISC and, therefore, ΦΔ decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ΦΔ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ΦΔ upon addition of increasing amounts of the latter.
AB - We have investigated the effect of a series of 18 solvents and mixtures of solvents on the production of singlet molecular oxygen (O2(1Δg), denoted as 1O2) by 9H-fluoren-9-one (FLU). The normalized empirical parameter ENT derived from ET(30) has been chosen as a measure of solvent polarity using Reichardt's betaine dyes. Quantum yields of 1O2 production ΦΔ decrease with increasing solvent polarity and protic character as a consequence of the decrease of the quantum yield of intersystem crossing (ΦISC). Values of ΦΔ of unity have been found in alkanes. In nonprotic solvents of increasing polarity, ΦISC and, therefore, ΦΔ decrease due to solvent-induced changes in the energy levels of singlet and triplet excited states of FLU. This compound is a poor 1O2 sensitizer in protic solvents, because hydrogen bonding considerably increases the rate of internal conversion from the singlet excited state, thus diminishing ΦΔ to values much lower than those in nonprotic solvents of similar polarity. In mixtures of cyclohexane and alcohols, preferential solvation of FLU by the protic solvent leads to a fast decrease of ΦΔ upon addition of increasing amounts of the latter.
UR - http://www.scopus.com/inward/record.url?scp=0037230773&partnerID=8YFLogxK
U2 - 10.1002/hlca.200390039
DO - 10.1002/hlca.200390039
M3 - Article
AN - SCOPUS:0037230773
SN - 0018-019X
VL - 86
SP - 384
EP - 397
JO - Helvetica Chimica Acta
JF - Helvetica Chimica Acta
IS - 2
ER -