Applications of Three-Coordinate Organoboron

Applications of Three-Coordinate Organoboron - 4574 Chem....

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Applications of Three-Coordinate Organoboron Compounds and Polymers in Optoelectronics Christopher D. Entwistle and Todd B. Marder* Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, U.K. Received March 15, 2004. Revised Manuscript Received May 24, 2004 Three-coordinate boron, with its vacant p-orbital, is a useful π -acceptor in conjugated organic molecules. These materials have interesting linear, as well as first- and second- order nonlinear, optical properties, exhibit two-photon-excited fluorescence and fluoride ion sensing properties, and can serve as emissive and/or electron-transport layers in OLEDs. Polymers containing three-coordinate boron in the main chain also display interesting optical properties. These features are all addressed in this short review. Introduction With its vacant p z orbital, three-coordinate boron is inherently electron poor and is a strong π -electron acceptor, which can lead to significant delocalization when conjugated with an adjacent organic π -system. Unlike other strong π -acceptors, however, in three- coordinate organoboranes, boron may even function as a σ -donor due to its low electronegativity compared with that of carbon. 1 The boron p z orbital is readily attacked by nucleophiles such as water, resulting in either bond cleavage or the formation of a four-coordinate borate species, which can no longer participate effectively in conjugation with adjacent π -systems. As with many other low-coordinate systems, a common strategy in the synthesis of compounds containing three-coordinate boron is to provide kinetic stability by blocking the approach of nucleophiles with sterically demanding substituents. Bulky aryl groups, such as the mesityl (2,4,6-trimethylphenyl), fluoromesityl (2,4,6-tris(trifluo- romethyl)phenyl), or tripyl (2,4,6-triisopropylphenyl) groups, are particularly effective, as steric conjestion around boron results in the formation of propeller-like structures where the ortho -substituents on the aryl ligands form a “cage” around the vacant p z orbital. This is particularly apparent in trimesitylborane ( 1 ) (Figure 1), which is an exceptionally unreactive borane. Compounds Containing the Dimesitylboryl Group In 1971, Williams and co-workers, who were investi- gating the photochemistry of organoboron compounds at Kodak, discovered that, while triphenylborane was subject to photodegradation in the presence of donor solvents, trimesitylborane was photochemically inert in all solvents. 2 Furthermore, they discovered that two mesityl groups were sufficient to provide an unusual degree of stability, which encouraged them to embark upon a photophysical study of para -substituted aryldi- mesitylboranes 2 (Figure 2). 3
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/27/2011 for the course CHEM 2211L taught by Professor T.a. during the Spring '08 term at University of Georgia Athens.

Page1 / 12

Applications of Three-Coordinate Organoboron - 4574 Chem....

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online