Review
Photophysics in bipyridyl and terpyridyl platinum(II) acetylides

https://doi.org/10.1016/j.ccr.2006.03.007Get rights and content

Abstract

The photophysical properties of mononuclear PtII chromophores of the general structural formulae: Pt(LL)(Ctriple bondCR)2 and [Pt(LLL)(Ctriple bondCR)]+ (LL = substituted or unsubstituted 2,2′-bipyridine; LLL = substituted or unsubstituted 2,2′:6′,2″-terpyridine; R = aryl or alkyl) are described. Topics related to their preparation, spectroscopy, photochemistry, and photophysics are reviewed.

Introduction

Since the original description of Pt(phen)(Ctriple bondCPh)2 by Che and co-workers in 1994 [1], the number of related square planar platinum(II) acetylides bearing a lone polyimine ligand has enormously expanded. Such molecules have demonstrated promise in diverse applications including optical power limiting [2], [3], electroluminescence [4], singlet oxygen photosensitization [5], [6], photocatalytic hydrogen production [7], cation sensors [8], [9], [10], vapochromism [11], medicinal chemistry [12], and as extrinsic luminescent probes [13]. In general, these chromophores are rich in terms of their photophysics, combining properties of traditional coordination compounds and organometallics within the same structure. This amalgamation has inspired creativity in molecular design, uncovering new and sometimes unexpected photophysical properties in seemingly straightforward platinum(II) complexes. The current review will limit its focus to the photophysical properties of mononuclear PtII chromophores bearing a combination of one or more alkyl- or arylacetylide ligands in concert with a lone polyimine (2,2′-bipyridine or 2,2′:6′,2″-terpyridine) fragment.

Section snippets

Synthetic approaches to bipyridyl and terpyridyl platinum(II) acetylides

The syntheses of compounds which are the subject of this review require relatively facile procedures. The synthesis generally departs either directly from K2PtCl4 [14] (acidic aqueous reaction conditions) or from Pt(DMSO)2Cl2 [15] (organic solvents) where the polyimine ligand displaces appropriate labile ligands, producing the corresponding Pt(LL)Cl2 or [Pt(LLL)Cl]+ species. The introduction of the acetylide unit(s) to the platinum(II) center is readily accomplished through a

Ground state electronic spectra, electrochemistry, and electronic structure calculations

Pt(LL)(Ctriple bondCR)2 and [Pt(LLL)(Ctriple bondCR)]+ molecules display characteristic low energy absorption bands that span wavelengths from approximately 350 nm to beyond 600 nm, depending upon the nature of the polyimine and acetylide ligands. In molecules where acetylide-localized π–π* transitions reside at high energies, the low energy absorption bands have been proposed to originate predominately from metal-to-ligand charge transfer (MLCT) transitions [4], [18], [19], [20]. Cyclic voltammetry data generally

Photoluminescence properties

Fig. 3 displays the photoluminescence spectra of compounds 14 measured in CH2Cl2 at room temperature under optically dilute conditions. Upon photoexcitation into their respective charge transfer transitions, complexes 14 exhibit broad and structureless photoluminescence over a region spanning 500–750 nm. The large Stokes shift, relatively long lifetime and susceptibility to quenching by dioxygen, suggest that the photoluminescence emanates from a triplet charge transfer excited state [18], [19]

Supra-nanosecond spectrometry

While luminescence spectroscopy has been widely applied to the study of Pt(II) polyimine acetylides, there have only been a handful of transient absorption investigations [2], [3], [19], [26], [27], [28], [33], [38], [39], [40] along with a single time-resolved infrared study [19]. The latter can be easily understood in terms of the low IR-absorption cross-sections uniformly observed for acetylide stretching frequencies, rendering their detection rather difficult. Regardless, a few Pt(II)

Concluding remarks

Although the primary motivation for research in this area largely stems from the potential applications of these chromophores across a variety of disciplines, the fact remains that there are many interesting questions remaining and several lines of investigation worth further exploration. This contribution was intended to outline current work in the field related predominately to the photophysical processes in bipyridyl and terpyridyl platinum(II) acetylides. Even within this seemingly small

Acknowledgements

We gratefully acknowledge the NSF (CAREER Award CHE-0134782), the AFOSR (FA9550-05-1-0276), the ACS-PRF (44138-AC3 and 36156-G6), and Bowling Green State University (Technology Innovation Enhancement Award) for their generous support of our own research projects relevant to this review. All transient absorption measurements described in this review were performed in the Ohio Laboratory for Kinetic Spectrometry at BGSU. We thank Dr. Albert Okhrimenko for acquiring the near-IR emission spectrum

References (44)

  • C.W. Chan et al.

    Coord. Chem. Rev.

    (1994)
  • K. Sonogashira et al.

    J. Organomet. Chem.

    (1978)
  • S.L. James et al.

    J. Organomet. Chem.

    (1997)
  • W. Sun et al.

    Appl. Phys. Lett.

    (2003)
  • F. Guo et al.

    Inorg. Chem.

    (2005)
  • S.-C. Chan et al.

    Chem. Eur. J.

    (2001)
  • D. Zhang et al.

    Org. Lett.

    (2003)
  • Y. Yang et al.

    J. Org. Chem.

    (2004)
  • D. Zhang et al.

    J. Am. Chem. Soc.

    (2004)
  • Q.-Z. Yang et al.

    Inorg. Chem.

    (2004)
  • Q.-Z. Yang et al.

    Eur. J. Inorg. Chem.

    (2004)
  • V.W.-W. Yam et al.

    Organometallics

    (2001)
  • W. Lu et al.

    Chem. Eur. J.

    (2003)
  • D.-L. Ma et al.

    Chem. Commun.

    (2005)
  • K.M.-C. Wong et al.

    Organometallics

    (2004)
  • K.D. Hodges et al.

    Inorg. Chem.

    (1975)
  • V.Y. Kukushkin et al.

    Inorg. Synth.

    (2002)
  • M. Hissler et al.

    Inorg. Chem.

    (2000)
  • C.E. Whittle et al.

    Inorg. Chem.

    (2001)
  • Q.-Z. Yang et al.

    Inorg. Chem.

    (2002)
  • V.W.-W. Yam et al.

    Angew. Chem. Int. Ed.

    (2003)
  • F. Hua et al.

    Inorg. Chem.

    (2005)
  • Cited by (270)

    • Luminescent supramolecular assemblies

      2023, Comprehensive Inorganic Chemistry III, Third Edition
    View all citing articles on Scopus

    ISPPCC 16 contribution.

    View full text