Microcomputerized ultrahigh-speed transient digitizer and luminescence lifetime instrument

A high-speed transient digitizer and a versatile luminescence lifetime insrument are described. A Z-80-based microcomputer permits rapid acquisition of transients, signal averaging, baseline subtraction, single or double exponential decay fitting, deconvolution, and graphics display of the transient and its semilogarithmic plot of decays on an oscillo-scope or an X-Y plotter. Data can also be transferred to more powerful computers for further data reduction or higher quality plots. Applications that exploit the speed and convenience of the system are described.     

Luminescent transition metal complexes as sensors: structural effects on pH response

A series of luminescent transition metal complexes using the pH-sensitive ligand 5-carboxy-1,10-phenanthroline has been synthesized and characterized. The complexes, based on Ru(II) and Re(I), show monotonic changes in both luminescent intensity and lifetime with pH values over the range 2 < pH < 9. The impact of various structural features on both the range of pH sensitivity and dynamic response was studied using both intensity and lifetime measurements. It was possible to predictably tune the pH sensitivity range over about 1.5 pKa units. While significant variation in the dynamic response range was observed, the correlation with structural features needs further study.     

Luminescence-Based Oxygen Sensors: ReL(CO)3Cl and ReL(CO)3CN Complexes on Copolymer Supports

A new class of luminescent rhenium complexes has been tested as oxygen sensors based on luminescent quenching. ReL(CO)₃Cl and ReL(CO)₃CN (L = 2,2-bipyridine or 1,10-phenanthroline and substituted analogues) have several features that seem to indicate suitability as oxygen sensors. These include simple synthesis, long excited-state lifetimes, and high luminescence quantum yields. Intensity and lifetime oxygen quenching measurements were used to study the complexes in various polymer supports including homopolymers of PDMS (polydimethylsiloxane), a methacryloxy containing PDMS (Gp-163), and trimethylsilylmethylmethacrylate (T3642), and copolymers containing Gp-163 and T3642. In contrast to previous studies utilizing [Ru(4,7-diphenyl-1,10-phenanthroline)₃]²⁺ as an oxygen sensor, quenching of the Re complexes proved much more sensitive to the polymer support. With suitable supports, the rhenium chloro complexes demonstrated significant quenching; but the cyano complexes, in spite of being robust in solution, exhibited severe photochemical instability in polymers. The potential of this class of complexes as oxygen sensors and as molecular probes as well as the ramifications in the design of new and different types of sensors is discussed.     

Oxygen Sensors Based on a Quenching of Tris-(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) in Fluorinated Polymers

Luminescence quenching of Ru(II) complexes by oxygen has proved a powerful method of quantitative oxygen analysis. It has become clear that the polymer support for the sensor molecule plays a pivotal role in the sensor performance. The current work is devoted to understanding how the physical and photophysical properties of a sensor respond to changes in polymer composition. An oxygen quenching study was conducted on [Ru(Ph₂phen)₃]Cl₂(Ph₂phen=4,7-diphenyl-1,10-phenanthroline), in copolymer supports consisting of GP-163 (a polydimethylsiloxane (PDMS) with varying amounts of pendant acrylate groups) combined with a number of alkyl methacrylates with long chain alkyl or fluorinated alkyl esters. Increasing the chain length or the degree of fluorination on the hydrocarbon chains enhances performance. However, there is an optimal chain length for the fluorinated hydrocarbons for sensitivity, linearity, and physical properties. Too long a chain yields reduced quenching sensitivity and yields cloudy polymers. All systems showed some degree of heterogeneity as indicated by nonlinear Stern-Volmer quenching plots, but their intensity quenching data could be successfully fit with a two-site model.     

On the causes of altered photophysics of luminescent metal complexes embedded in polymer hosts

A suite of luminescent Re(I) complexes has been prepared whose emissive properties are responsive to the probe's local environment. These complexes were embedded in a series of chemically similar polymers whose room temperature rigidity varied over a significant range. It is shown that the degree of local rigidity experienced by the embedded complexes significantly alters the observed emission in terms of both spectra and lifetime. Time resolved emission measurements show that the spectral shifts and lifetime complexity are correlated and track well the polymers' T(g) within the series. Fluorescence confocal microscopy did not show the presence of discrete domains, and thus, the environmental features responsible for the altered photophysics must be submicrometer in size.