ABSTRACT
Metal-directed macrocyclic assembly has been a remarkable research area in the realm of supramolecular chemistry. Over the past few decades, metal-directed self-assembly has proven to be a powerful tool in the synthesis of well-defined multimetallic architectures with increasing structural complexity based on metal−ligand interactions. The transition metal−containing macrocycles are generally designed to be sensitive and responsive upon electro-and/or photochemical stimuli. With the further introduction of various functional moieties on the tectons, the backbone can be modified as electron deficient or electron rich, and their interior as well as their exterior can be functionalized independently. This allows them
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 IntroductionAn 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].
