Excited state acidity of bifunctional compounds. 6. A novel, high fluorescence quantum yield, excited state intramolecular proton transfer compound: 2-hydroxyphenyl-lapazole in non-protic solvents

The synthesis of 2-hydroxyphenyl-lapazole (HPL) is reported for the first t ime. HPL in the first excited singlet state undergoes excited state intramo lecular proton transfer (ESIPT) in cyclohexane, with an overall fluorescenc e quantum yield of 0.15. This is an order of magnitude greater than that ob served for 2-hydroxyphenyl-benzoxazole (HBO), which has been extensively st udied and has a similar structure. At room temperature in non-protic solven ts, ESIPT in HPL attains equilibrium, whose constant (between normal and ta utomer species) is approximately 1.4. These observations suggest that HPL ( and its derivatives) is well worth investigating because it is easier to st udy (and may work more efficiently as a laser dye) than HBO. (C) 1999 Elsev ier Science S.A. All rights reserved.