INTENSE PHOSPHORESCENCE TRIGGERED BY ALCOHOLS UPON FORMATION OF A CYCLODEXTRIN TERNARY COMPLEX

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.