Singlet oxygen-induced photodegradation of the polymers and dyes in optical sensing materials and the effect of stabilizers on these processes.

A comprehensive study of photodegradation processes in optical sensing materials caused by photosensitized singlet oxygen in different polymers is presented. The stabilities of the polymers are accessed in the oxygen consumption measurements performed with help of optical oxygen sensors. Polystyrene and poly(phenylsilesquioxane) are found to be the most stable among the polymers investigated, whereas poly(2,6-dimethyl-p-phenylene oxide) and particularly poly(methyl methacrylate) and their derivatives show the fastest oxygen consumption. The effect of the stabilizers (singlet oxygen quenchers) on the oxygen consumption rates, the photostability of the sensitizer, and the total photon emission (TPE) by singlet oxygen is studied. 1,4-Diazabicyclo[2.2.2]octane (DABCO) was found to significantly reduce both the TPE and the oxygen consumption rates, indicating its role as a physical quencher of singlet oxygen. The addition of DABCO also significantly improved the photostability of the sensitizer. The N-alkylated derivative of DABCO and DABCO covalently grafted to the polystyrene backbone are prepared in an attempt to overcome the volatility and water solubility of the quencher. These derivatives as well as other tertiary amines investigated were found to be inefficient as stabilizing agents, and some of them even negatively affected the oxygen consumption rates.

Tuning the dynamic range and sensitivity of optical oxygen-sensors by employing differently substituted polystyrene-derivatives.

Ten different polystyrene-derivatives were tested with respect to their potential use as matrix materials for optical oxygen sensors in combination with the platinum(II) meso-tetra(4-fluorophenyl)tetrabenzoporphyrin as indicator dye. Either halogen atoms or bulky residues were introduced as substituents on the phenyl ring. A fine-tuning of the sensor sensitivity was achieved, without compromising solubility of the indicator in the matrix by providing a chemical environment very similar to polystyrene (PS), a standard matrix in optical oxygen sensors. To put the results into perspective, the studied materials were compared to PS regarding sensitivity of the sensor, molecular weight and glass-transition temperature. The materials promise to be viable alternatives to PS with respect to the requirements posed in various sensor application fields. Some of the polymers (e.g. poly(2,6-dichlorostyrene)) promise to be of use in applications requiring measurements from 0 to 100% oxygen due to linearity across this range. Poly(4-tert-butylstyrene) and poly(2,6-fluorostyrene), on the other hand, yield sensors with increased sensitivity. Sensor stability was evaluated as a function of the matrix, a topic which has not received a lot of interest so far.

Organic super-acceptors with efficient intramolecular charge-transfer interactions by [2+2] cycloadditions of TCNE, TCNQ, and F4-TCNQ to donor-substituted cyanoalkynes.

Rivaling the best one: Thermal [2+2] cycloadditions of TCNE, TCNQ, and F(4)-TCNQ to N,N-dimethylanilino-substituted cyanoalkynes afforded a new class of organic super-acceptors featuring efficient intramolecular charge-transfer interactions. These acceptors rival the acceptor F(4)-TCNQ in the propensity for reversible electron uptake as well as in electron affinity (see figure), which makes them interesting as p-type dopants for potential application in optoelectronic devices.Thermal [2+2] cycloadditions of tetracyanoethene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ), and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)-TCNQ) to N,N-dimethylanilino-substituted (DMA-substituted) alkynes bearing either nitrile, dicyanovinyl (DCV; -CH==C(CN)(2)), or tricyanovinyl (TCV; -C(CN)==C(CN)(2)) functionalities, followed by retro-electrocyclization, afforded a new class of stable organic super-acceptors. Despite the nonplanarity of these acceptors, as revealed by X-ray crystallographic analysis and theoretical calculations, efficient intramolecular charge-transfer (CT) interactions between the DMA donors and the CN-containing acceptor moieties are established. The corresponding CT bands appear strongly bathochromically shifted with maxima up to 1120 nm (1.11 eV) accompanied by an end-absorption in the near infrared around 1600 nm (0.78 eV) for F(4)-TCNQ adducts. Electronic absorption spectra of selected acceptors were nicely reproduced by applying the spectroscopy oriented configuration interaction (SORCI) procedure. The electrochemical investigations of these acceptors by cyclic voltammetry (CV) and rotating disc voltammetry (RDV) in CH(2)Cl(2) identified their remarkable propensity for reversible electron uptake rivaling the benchmark compounds TCNQ (E(red,1)=-0.25 V in CH(2)Cl(2) vs. Fc(+)/Fc) and F(4)-TCNQ (E(red,1)=+0.16 V in CH(2)Cl(2) vs. Fc(+)/Fc). Furthermore, the electron-accepting power of these new compounds expressed as adiabatic electron affinity (EA) has been estimated by theoretical calculations and compared to the reference acceptor F(4)-TCNQ, which is used as a p-type dopant in the fabrication of organic light-emitting diodes (OLEDs) and solar cells. A good linear correlation exists between the calculated EAs and the first reduction potentials E(red,1). Despite the substitution with strong DMA donors, the predicted EAs reach the value calculated for F(4)-TCNQ (4.96 eV) in many cases, which makes the new acceptors interesting for potential applications as dopants in organic optoelectronic devices. The first example of a charge-transfer salt between the DMA-substituted TCNQ adduct (E(red,1)=-0.27 V vs. Fc(+)/Fc) and the strong electron donor decamethylferrocene ([FeCp*(2)]; Cp*=pentamethylcyclopentadienide; E(ox,1)=-0.59 V vs. Fc(+)/Fc) is described. Interestingly, the X-ray crystal structure showed that in the solid state the TCNQ moiety in the acceptor underwent reductive sigma-dimerization upon reaction with the donor.

A planar waveguide optical sensor employing simple light coupling.

An optical sensor concept utilizing the sensing layer as the light propagating layer and a new method to couple light into a planar waveguide is presented. The concept enables simple manufacturing by coating or printing techniques and the integration of organic (plastic) opto-electronic components.