Modification of indicators for carbon dioxide determination and application in some polimer matrices

In most of the common designs, pH optodes rely on weak acidic dyes whose dissociated and undissociated forms have different absorption or emission maxima. In this work dimethylamino bearing fluorescent rich Schiff bases N1,N2-bis{(E,2E)-3-[4- dimethylamino)phenyl]-2-propenylidene}-1,2-ethanediamine (SB-I), N1{(E,2E)-3-[4- dimethylamino)phenyl]-2-propenylidene}-N4,N4-dimethyl-1,4-benzene-diamine (SB-II), 4- {(1E, 3E)-3-[(4-cholorphenyl)imino]-1-propenyl}-N,N-dimethylaniline (CPIPA) and N,Ndimethyl- 4-{(1E,3E)-3-[(4-nitrophenyl)imino]-1-propenyl}aniline (NPIPA) have been used for pH sensing in the solid matrices of ethyl cellulose (EC) and plasticized PVC. Spectral characterization, quantum yield and acidity constant (pKa) calculations of the Schiff bases were performed in the conventional solvents or in the solid matrices of PVC and EC. The immobilized Schiff bases SB-I (pKa= 4.27 in PVC), SB-II (pKa= 10.68 in PVC), CPIPA (pKa= 10.32 in PVC) and NPIPA (pKa= 8.8 in PVC) exhibited absorption and emission based optical response to proton in the pH range of 2.0-7.0, 8.0-12.0, 7.0-12.0 and 8.0-12.0 respectively. Immobilization of the dye effectively enhanced the fluorescence of these materials compared to solution. Responses of the sensor slides were fully reversible within the dynamic working range and the response times were less than 1 min. Also, NPIPA was tested for carbon dioxide determinations in ethyl cellulose matrix. The response of the sensor composition to gaseous carbon dioxide has been evaluated in the absence and presence of the perfluoro compound (PFC) and tetrabutylammonium hidroxide (TBAOH).