Optical oxygen sensors based on platinum porphyrin dyes encapsulated in ORMOSILS

A strategic approach to develop an ideal sensor platform is addressed. Novel quenchometric O-2 sensing materials with 100-fold adjustable sensitivity (I-N2/I-O2 from 3 to over 300), reverse and fast response (1 s), linear calibration, and long-term stability are developed. These materials are spin-casted composite ORMOSILs (organically modified silicates) xerogel films sequestered with luminophore Pt(II) octaethylporphine (PtOEP) and Pt(II) meso-tetra(N-methyl-4-pyridyl)porphyrin tetrachloride (PtTMP). The composite xerogels studied are pentafluorophenylpropyltrimethoxysilane (PFTMOS)/noctyltrimethoxysilane (C8TMOS)/tetramethoxysilane (TMOS) and 3,3,3-trifluoropropyltrimethoxysilane (TFTMOS)/n-propyltrimethoxysilane (C3TMOS). Luminescence spectroscopy (steady state and time resolved) have been used to investigate their analytical figures of merit for gaseous 02 sensing and to determine the underlying reasons for the observed performance. Results show that, except for PtTMP-doped PFTMOS/C8TMOS/TMOS, all other xerogel composites show linear Stern-Volmer relationship and the single exponential time-resolved intensity decay, which indicate the homogeneous environment of the luminophore. For PtTMP-doped PFTMOS/C8TMOS/TMOS xerogels, the Stern-Volmer plots are non-linear and the time-resolved intensity decay profiles are best fitted by double exponential decay model, which are resulted from the heterogeneous environment of the luminophore. The sensitivity of the sensing materials can be tuned by adjusting the xerogel composition and luminophore. For PtOEP-doped PFTMOS/C8TMOS/TmOS, while keeping C8TMOS and TMOS at the same mol ratio, sensitivity (I-N2/I-O2) decreases from 333 to 246 with increased PFTMOS% from 0 to 30%, which is due to the decreased bimolecular quenching constant (kg). However, I-N2/I-O2 = 3 was observed from PtTMP-doped PFTMOS/C8TMOS/TMOS. For PtTMP-doped TFTMOS/C3TMOS, sensitivity increases with increased TFT-MOS% from 0 to 50% and decreases with further increased TFTMOS% from 50 to 100%, which is mainly due to corresponding increase and decrease of k(q). An optimized composition with high sensitivity is observed at 10 PFTMOS/45C8TM05/45 C8TMOS with I-N2/I-O2 = 330. (C) 2010 Elsevier B.V. All rights reserved.