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Brennan, John

Position: 
Professor and Vice Chair Undergraduate Program

John Brennan Phone: 848-445-5677
E-mail: E-mail
FAX: 732-445-5312
Lab: 732-445-5678
Office: Wright Rieman Labs 284/270
Mail: Chemistry & Chemical Biology, 610 Taylor Road, Piscataway, NJ 08854
Education
  • B.S. 1980, SUNY-Albany
  • Ph.D. 1986, U.CA-Berkeley
  • NSF Postdoctoral Fellow 1986-87
  • E.P.A. Cephalosporin Junior Research Fellow, Oxford 1987-1989
  • Henry Rutgers Research Fellow 1990-1992

Research Summary

In recent years, our program has been focused on the synthesis and characterization of lanthanide molecules and clusters with extraordinary NIR emission properties. Chalcogen based anions (i.e. SC6F5-, SeSe2-, Te2-) are particularly useful for the preparation of highly NIR emissive materials, because the relatively long, weak Ln-E bond effectively decreases energy transfer and vibrational quenching processes. Our molecular efforts currently focus on the design and synthesis of new types of chalcogenolate ligands intended to produce lanthanide compounds with superior chemical/electronic properties. Our cluster program is devoted to the preparation of increasingly large/complex cluster compounds, using chalcogen based anions to encapsulate and ‘stabilize’ cluster cores with a surprising variety of ligand types. The utility of these molecules and clusters in emerging polymer based optical fiber technologies has been demonstrated in collaboration with Ajith Kumar and Richard Riman.

Lanthanide Oxide Clusters

Lanthanide Oxide Clusters 1 The persistent request for ‘air stable’ emissive clusters led us to investigate the synthesis of oxide clusters with chalcogen encapsulants. Santanu Banerjee's first product in this area was from a reaction with SeO2 that gave (THF)8Ln8Se2O2(SePh)16. The Nd compound was particularly significant as it was the most efficient molecular source of 1.34 µm emission currently available (up until the fluoride cluster mentioned below), and this energy is important to the telecommunications industry.

Lanthanide Oxide Clusters 2 The compound was also notable as the first molecular Nd compound to emit at 1.81 µm. Santanu's latest oxocluster result is a highly emissive Nd12O6 compound shown below. The structural characteristics of the oxo core of this material are distinctly similar to those of solid state Nd2O3, but the compound differs in that it emits NIR radiation at 1352 nm, while vibations of the Nd2O3 lattice quench this emission. Note that in the Nd12 cluster both phonon coupling and concentration quenching lead to elimination of the 1840 nm emission found in the previously described octanuclear cluster.

Lanthanide Fluorides

Lanthanide FluoridesThe apparent stability of these oxo materials with respect to disproportionation led Mike Romanelli to attempt the synthesis of even more stable cluster cores, and his first success in this area came with the isolation of the nanoscale product
(py)24Ln28F68(SePh)16 (Ln = Pr, Nd). The 44% quantum efficiency of the Nd cluster is more than twice that of our oxide clusters.

Chalcogenolate complexes

Chalcogenolate complexesOur lanthanide work has led, indirectly, to the synthesis and characterization of novel main group and transition metal chalcogenolate complexes with extraordinary physical properties, i.e. the II-VI precursors of Yifeng Cheng. We are still pursuing a number of chemically interesting synthetic targets with significant CVD applications. These chelating ligands are important in Ln chemistry because they form relatively air stable products, as found in the homoleptic Ln(III) pyridinethiolates of Mike Berardini.

Virtually air stable thiolates can also be prepared with fluorinated thiolate ligands. Jonathan Melman has described the synthesis of Ln(SC6F5)n (n = 2, 3) and Kieran Norton has just completed a structural and spectroscopic investigation of the analogous fluorinated phenoxides. These fluorinated compounds are considerably more stable than their C6H5 counterparts and they are soluble in hydrocarbon solvents. Using these ligands Mark Fitzgerald prepared the first toluene soluble lanthanide sulfido and selenido clusters.


Publications


Research Areas: 
Inorganic Chemistry
Research Areas: 
Materials Chemistry

Rutgers, The State University of New Jersey