Optical oxygen sensing based on triplet-triplet decay of platinum octaethylporphyrin-polystyrene film using time-resolved spectroscopy by laser flash photolysis

Abstract

Determination of oxygen concentration is important in various fields of chemical, clinical analysis and environmental monitoring [1,2]. Recently, much attention has been paid to optical sensors based on the luminescence quenching of the indicator [3] such as polycyclic aromatic hydrocarbons [4][5][6], metalloporphyrins [7][8][9] and transition metal complexes [10][11][12], by oxygen, because of their high sensitivity and specificity. Many studies on optical sensing have explored the luminescence intensity change by oxygen. Although intensity measurements are simple, the observed intensity depends on the thickness of the sensing film, scattering light from background or the concentration of dye in the film. We reported the optical oxygen sensing system using luminescence intensity change of platinum octaethylporphyrin-polystyrene (PtOEP-PS) film by oxygen [8]. However, the oxygen sensing mechanism of PtOEP-PS film has not been clarified. On the other hand, lifetime measurements are concerned only with the rate of decrease of the light emission following a flash of excitation light and do not depend on the absolute intensity of the emitted light. The concept of using lifetime measurement of photoexcited triplet state of dye has proven to be attractive for optical oxygen sensing. It has important advantages for certain applications compared to the steady state luminescence quenching based methods [13]. As reported previously, the optical oxygen sensing system based on triplet-triplet absorption quenching of zinc porphyrin-polymer film by oxygen using timeresolved spectroscopy by laser flash photolysis has been developed [14]. By using this method, the oxygen sensing mechanism of PtOEP-PS will be clarified.In this letter, we describe the properties of optical oxygen sensing based on triplet-triplet absorption decay of PtOEP-PS film by oxygen using a time-resolved spectroscopy by laser flash photolysis. ExperimentalPtOEP (obtained from Porphyrin Products, Logan, UT, USA)-PS (average M.W. 280 000, GPC grade obtained from Aldrich, Milwaukee, WI) films were formed by casting mixture of 30-wt % PS in toluene and PtOEP onto non-luminescence glass slides. The concentration of PtOEP in PS was approximately 3.0 × 10 -5 mol dm -3 . The films were dried at room temperature and stored in dark prior to use. The PtOEP-PS film has a good photostability under laser irradiation. Laser flash photolysis was carried out using Nd-YAG OPO laser (Spectra Physics, pulse width 10 ns) at room temperature. The excitation wavelength was 535 nm, which is attributed to Q-band of PtOEP. The experimental setup for optical oxygen sensing using laser flash photolysis are reported previously [14]. The decay curves of photoexcited triplet state of PtOEP-PS film were obtained by averaging 256 single shots using a storage oscilloscope (SONYTektronix TDS360). Decay curves were analyzed without deconvolution by fitting with the following equation: 885Optical oxygen sensing based on triplet-triplet decay of platinum octaethylporphyrin-polystyrene film usin...

Organic Electroluminescent Sensor for Pressure Measurement

“…Platinum (II) octaethylporphine (PtOEP), which is used as both oxygen sensor [2] and OLED [14], was adopted as an oxygen probe. The pressure or oxygen sensitivity of PtOEP was investigated in detail by Amao and his coworkers [15,16]. PtOEP was doped into the host material poly(vinylcarbazole) (PVK) at the ratio of 1:9 w/w PtOEP/PVK.…”