A. Prasanna de Silva

Combining luminescence, coordination and electron transfer for signalling purposes

Abstract The evolution of research in luminescent signalling at Queens University of Belfast is critically reviewed in the context of related work from the literature. Photoinduced electron transfer (PET) is found to be a robust design principle for such work. The possibilities raised by these signalling systems for sensing and switching operations are pointed out. Fluorescent PET signalling systems for s-block metal ions and relatives are classified according to the type of receptor employed. PET signalling systems, which exploit lanthanide lumophores are also woven into the discussion.

Fluorescent PET (photoinduced electron transfer) sensors

Fluorescent PET (photoinduced electron transfer) sensors are considered to be those molecular systems where the binding of ions and other species leads to the perturbation of the competition between the de-excitation pathways of fluorescence and electron transfer. The early developments in this field are traced and the design logic of these sensors is detailed. A variety of examples drawn from different areas of chemistry are classified according to the ‘fluorophore-spacer-receptor’ format and their photophysical behaviour is rationalized in terms of fluorescent PET sensor principles. Cases are pointed out where such experimental data are unavailable but desirable. During these discussions, the relevance of twisted fluorophore-receptor systems and the contrast with integrated fluorophore-receptor systems is noted. The utility of the fluorescence ‘on-off’ phenomenon in these PET sensors for the area of molecular photoionic devices is pointed out.

Fluorescent signalling crown ethers; switching on of fluorescence by alkali metal ion recognition and binding in situ

Sodium and potassium ions enhance the fluorescence quantum yield of the N-(9-anthrylmethyl) monoaza crown ethers (1) in methanol by factors of up to forty-seven while all other electronic spectral parameters remain unaltered.

Newer optical-based molecular devices from older coordination chemistry

This short review illustrates how the wealth of receptors and ligands available within coordination/supramolecular chemistry can serve as a launch-pad for producing information-handling optical-based molecular devices of various kinds: sensors, assay reagents, logic gates and even small-scale number processors. Such a diverse range of information-handlers allows the addressing of problems in different areas from a common viewpoint. The common viewpoint is strengthened further when we find that the design principles are quite small in number.

Direct visual indication of pH windows: ‘off–on–off’ fluorescent PET (photoinduced electron transfer) sensors/switches

1–3, which contain a fluorophore and two proton receptors with opposite PET (photoinduced electron transfer) characteristics, only display strong fluorescence within a pH window whose position and width are tunable.

Photo-induced electron transfer as a general design logic for fluorescent molecular sensors for cations

Abstract The reasons for the value of molecular fluorescence as a biosensing technique are outlined. The case of fluorescent sensors for cations is discussed with emphasis on a new general design logic employing the principle of photo-induced electron transfer.

Development of fluorescent microgel thermometers based on thermo-responsive polymers and their modulation of sensitivity range

Fluorescent molecular thermometers based on thermo-responsive linear polymer molecules such as poly(N-isopropylacrylamide) (PNIPAM) labelled with a polarity-responsive fluorescent molecule benzofurazan (BD) are the most sensitive known. Thermo-responsive PNIPAM and some related polymer microgel particles labelled with BD by emulsion polymerization have been prepared and their fluorescence properties in water as fluorescent thermometers studied. All the cross-linked polymer microgel particles dispersed in water fluoresce strongly as soon as each threshold temperature is exceeded. The nine kinds of microgel dispersion developed in this work thoroughly cover the sensitivity range from 18 to 47 °C. They are not only more sensitive than the previous fluorescent molecular thermometers based on other principles but also highly reproducible in their behaviour.

Arenedicarboximide Building Blocks for Fluorescent Photoinduced Electron Transfer pH Sensors Applicable with Different Media and Communication Wavelengths

A whole family of modular photoinduced electron transfer (PET) sensors has been constructed from a single simple reaction type with commercially available materials. This family, one member of which is shown here, possesses amine receptors for protons and arenedicarboximide fluorophores addressable at different wavelengths. Its pH-sensing behaviour is examined in solution and in polymer membrane matrices, which are crucial for the use of fluorescent PET sensors as optode pH monitors.

FLUORESCENT PET(PHOTOINDUCED ELECTRON TRANSFER) REAGENTS FOR THIOLS

Abstract Michael addition of thiois to an electron deficient alkene functional group in reagents (1)-(3) give rise to fluorescence quantum yield enhancements. In the absence of the thiol, photoinduced electron transfer (PET) takes place from the fluorophore to the alkene moiety. Such electron transfer is suppressed after the thiol reaction.

‘Off–on’ fluorescent sensors for physiological levels of magnesium ions based on photoinduced electron transfer (PET), which also behave as photoionic OR logic gates

The fluorescence of molecules 1–3 is enhanced by factors of up to 67 in the presence of magnesium and calcium ions in neutral water which allows the selective monitoring of magnesium ions under simulated physiological conditions and permits the construction of truth tables with OR logic when these molecules are viewed as ion input–photon output molecular devices.