Metallo-1,2-enedithiolates complexes

Deflning the excited state of an emissive molecule is essential to understanding its properties and potential applications. As with any assignment of electronic transitions, those of the metallo-1,2-enedithiolate complexes have relied on both... 

FIgu re 2 A representation of the typical HOMO of a metallo-1,2-enedithiolate complex. While the contribution of the metal d orbital to the HOMO is large in this representation, it is known to vary and this accounts for variations in the metal contributions to the excited states. 

Found in Tables 1 a-d is a list of known emissive metallo-1,2-enedithiolate complexes. The tables are arranged by ligand type and include excitation and emission maxima, excited state assignment, and lifetimes. 

In 1997, a new synthetic route [30-34,43] made available a range of heterocyclic-substituted metallo-l,2-enedithiolate complexes (Scheme 1). The heterocycle (Het) and R group are readily varied using this method. Metallo-1,2-enedithiolate complexes with appended pyridines, 2-pyrazine, and 2-quinoxaline are now available. While the R group is limited only by the availability of the a-bromo- or tosyl ketone required for this synthesis, to date only complexes where R = H, Me, and CH2CH2OAC (and several derivatives of CH2CH2OH) [34] have been prepared. 

This chapter is intended as an overview of the photophysical and photochemical properties of emissive metallo-l,2-enedithiolates. It includes a brief description of the use of luminescent platinum 1,2-enedithiolate complexes to develop new sensors. Metal derivatives of mnt, met (cw-l,2-dicarbomethoxy-ethylene-1,2-dithiolate), bdt, tdt, dmqdt and qdt as well as complexes of the general structure type (phosphine)2Pt(S2C2(Het)(R ) where Het = 2- or 4-pyridine and 2-quinoxaline will be discussed (Fig. 1). 

The study of emission 1,2-enedithiolates now represents a formidable body of literature, even though the chemistiy, photochemistry, and photophysical properties of metallo-l,2-enedithiolate complexes are not yet as well understood or developed as those of the group metallo-Vlll-diimine and metalloporphyrin complexes. However, recent developments in the synthesis of 1,2-enedithiolates have led to the discovery of room temperature emitters and complexes with useful properties. As new methods allow for the synthesis of yet unknown complexes in this family, the unique and useful properties of these complexes will become even more evident. Many of the heterocyclic-substituted 1,2-enedithiolates now available are dual emitters with a short-lived and analyte-quenchable long-lived excited states. Clearly, these dual emitters will have a unique place in the detection of quenching analytes since selective quenching of Ae long-lived excited state eliminates several problems encountered with luminescence-based sensing. 

As detection needs continually move to the specificity offered only by biological and chemical recognition, reactive chemical entities will play an increasingly important role. The discovery of new metallo-l,2-enedithiolates and the further study of the reactivity of these complexes is important to their potential use in detection. Much of the work described in this chapter is <5 years old, which underlies the importance of continued study. The reactivity of complexes with important analytes such as olefins (90) [see Chapter 6 in this volume (88)], oxygen, and organophosphates make metallo-l,2-enedithiolates of potential use as components in analyte detection strategies. 

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