Room temperature phosphorescence pH optosensor based on energy transfer

In this paper, the development of a room temperature phosphorescence (RTP) optosensor for pH monitoring in aqueous media based on the effect of the pH on the energy transfer from a phosphor molecule (acting as a donor) to an adequate mixture of pH-sensitive dyes (acceptors) is presented. The propose d optosensor, to our knowledge the first RTP optical sensor for pH develope d so far, is based on the immobilization in a solid support of a pH-insensi tive phosphor molecule along with a mixture of three pH-sensitive dyes. 6-B romo-2-naphthyl sulfate (BNS) and alpha -bromoaaphthalene (BrN) are compare d as donor molecules, because both can produce significant RTP emission in aqueous media (without deoxygenation) when retained in a polymeric resin or encapsulated in a rigid sol-gel matrix. Absorption spectra of the mixture of phenol red (PhR), bromocresol purple (BCP) and bromophenol blue (BPB) in a concentration ratio of 10(-5):5 x 10(-6):10(-5) mol/l, respectively, pos sesses a desirable spectral overlap with the emission spectra of the donors (BNS and BrN) in a pH range around 3.5-9.2. Consequently, nonradiative ene rgy transfer occurs from the phosphor molecules to the mixture of pH indica tor dyes. An increase in the pH of the solution causes an absorption increa se of the mixture of the pH indicators (acceptors) and, therefore, an incre ase in the amount of energy transfer occurs which brings about a decrease o f the RTP emission. Thus, any changes in the absorption of the mixture of t he three pH indicators are detected as measurable changes in the RTP emissi on of the sensing material. The proposed RTP optosensor has been evaluated for pH monitoring of different water samples. (C) 2001 Elsevier Science B.V . All rights resented.