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to be potentially employed as probes for molecular recognition/
sensing and encapsulation. In this chapter, we highlight the recent
advances made in the photophysical and photochemical properties
of metallacyclic supramolecules, and, in particular, focus on their
potential applications with respect to molecular recognition and
sensing.
10.1
Introduction
An important aim of photophysics and photochemistry is to design
structurally organized and functionally integrated artificial systems
that are capable of elaborating the energy and information input
by photons to perform useful functions such as sensing of the
microscopic environment on a molecular level, processing and
storage of information, transformation and storage of solar energy,
and so on. These functions are routinely performed by nature and
are quintessential to the survival of life on the earth. A sensor is
generally understood to be a device that transforms an event into
an analytically useful and measurable signal for the presence of
matter or energy. Desired properties of a chemical sensor include
high sensitivity, a large dynamic range, high selectivity or specificity
to a target analyte, relatively low cross-sensitivity to interferents,
perfect reversibility of the physicochemical detection or sensing
process with short sensor recovery and response times, and long-
term stability of the sensor and sensing material [1
−
10]. The high
sensitivity and specificity on the one hand and perfect reversibility
on the other hand impose contradictory constraints on the sensor
design since high sensitivity and selectivity are typically associated
with strong interactions, whereas perfect reversibility requires
weak interactions, therefore, a compromise is requisite. The signals
generated by such an event should ideally be detectable both in close
vicinity as well as at remote distances. It should be different from any
signal generated from the unspecific background and the unbound
sensor. Moreover, random and uncontrolled generation of the output
must be avoided and the desired information is only reported on
request. Furthermore, the important aspects of designing a sensor
include analytical affinity, choice of chromophore or fluorophore, the
binding selectivity, the signaling mechanism, and the immobilization
method [1
−
13].
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