A. Ponce et al., INTENSE PHOSPHORESCENCE TRIGGERED BY ALCOHOLS UPON FORMATION OF A CYCLODEXTRIN TERNARY COMPLEX, Journal of physical chemistry, 97(42), 1993, pp. 11137-11142
Intense phosphorescence is observed when alcohols (ROH) are introduced
to aqueous solutions containing 1-bromonaphthalene (1-BrNp) and a glu
cosyl-modified cyclodextrin (Gbeta-CD). Steady-state and time-resolved
luminescence measurements and equilibrium constant data are consisten
t with phosphorescence arising from 1-BrNp as part of a 1-BrNp-Gbeta-C
D.ROH ternary complex. The association of the 1-BrNp to Gbeta-CD is in
creased in the presence of the alcohols (K = 800 M-1 in the absence of
ROH and K = 1900-3400 M-1 in the presence of ROH with the exception o
f cyclohexanol where K = 760 M-1). However the phosphorescence quantum
yields show no obvious correlation with the apparent formation consta
nts of the ternary complex. For instance, the ternary complex of cyclo
hexanol exhibits the highest phosphorescence quantum yield (phi(e) = 0
.035) despite possessing the smallest formation constant. Stern-Volmer
analysis shows that the phosphorescence enhancement induced by alcoho
l is related to its effectiveness in shielding photoexcited 1-BrNp fro
m oxygen. The rate constants for oxygen quenching decrease generally a
s the bulkiness of the alcohol increases. Accordingly, tert-butyl alco
hol and cyclohexanol give rise to the smallest oxygen quenching rate c
onstants and the highest emission quantum yields. The ability of alcoh
ols to trigger an intense luminescence response is a first step in the
development of an optical scheme to detect alcohols. The advantage of
strategies using a 1-BrNp.Gbeta-CD.ROH ternary complex is that alcoho
l detection occurs by the appearance of bright green phosphorescence r
elative to a photonically silent background.