Cyclodextrin-Induced Room-Temperature Phosphorescence of 1-Bromo-2-naphthol upon Formation of Ternary Complexes

Abstract

The inclusion constant for the 1:1 binary complex between 1-bromo-2-naphthol and β-cyclodextrin in aqueous solution was determined by a spectrofluorimetric method. On the basis of MO calculations, a possible structure of this complex was proposed and compared with those formed by two related naphthol derivatives. After the addition of different alcohols (linear, branched, and cyclic) to the 1-bromo-2-naphthol–β-cyclodextrin solution, a significant enhancement of the room-temperature phosphorescence (RTP) was observed. Both the formation constants and stoichiometries of the formed ternary complexes were determined from RTP data with the use of the computational program EPSILON. It was verified that RTP was also induced by adding different apolar liquids (cyclohexane and 1,3-dibromopropane) as the third component instead of alcohols. Of all the examined compounds, cyclohexanol produced both the largest RTP signal and the more stable ternary complex. The RTP calibration graph for 1-bromo-2-naphthol in the presence of both β-cyclodextrin and cyclohexanol was linear for the range of concentrations between 0.6 and 4.0 μg mL⁻¹ with a limit of detection of 0.2 μg mL⁻¹, with a relative standard deviation (n = 4) of 4%, for 2.2 μg mL⁻¹.