The Interaction of Light and Small Molecules with Certain Boron Hydrides.


                                     Dr. Michael Londesborough

     Institute of Inorganic Chemistry of the AS CR, v.v.i., 250 68 Husinec-Řež, Czech Republic



The boron hydrides are a group of compounds new to our planet.  There is no mechanism leading to
their synthesis in nature.  Instead it was German Chemist, Alfred Stock, who in 1912 first
developed the vacuum-line techniques necessary for their production. Over the last 100 years the
boron hydrides have proved to be the richest and most diverse of all hydride series apart from the
obvious exception of the hydrocarbons.  Our laboratories at the Institute of Inorganic Chemistry
have a long history, dating from an era of top secret research during the Cold War, in developing
the basic chemistry of the boron hydrides and applying their unique properties in areas such as
microelectronics, novel materials, and medicine.  This contribution will discuss new results^[1-3]
regarding the interaction of light and small molecules with certain boron hydrides.


The talk will focus on two main areas.  The first is our discovery of the propensity of bimetallic
boron hydride [L[4]M[2]B[10]H[10]] cluster systems, such as [(PMe[2]Ph)[4]Pt[2]B[10]H[10]] shown in
Fig.1, to reversibly capture small gaseous molecules such as O[2], CO and SO[2].  This property is
accompanied by a clear colour changes, and may be controlled via alterations in pressure or
irradiation with UV light.  Presented will also be our work on tuning this system to suit various
criteria, and our steps being taken towards the application of this property.



Fig.1. Picture of [(PMe[2]Ph)[4]Pt[2]B[10]H[10]] with a sequestered molecule of O[2] (left).  Graph
showing the release of sequestered molecule of O[2] via irradiation with UV light and the
associated colour changes (right).



The second part of the talk will be focused on our recent work describing the fluorescent
properties of the large boron hydride, B[18]H[22].  The photophysical properties of this compound
are unique amongst the boron hydrides, and include a blue-light fluorescence under UV irradiation
with a Φ=0.97 quantum yield.  In addition we have found that the tuning of the photophysical
properties of the highly fluorescent boron hydride cluster anti-isomer of B[18]H[22] is possible by
the straight-forward chemical substitution to produce 4,4’-(HS)[2]-anti-B[18]H[20], which
facilitates intersystem crossing from excited singlet states to a Abstract Image triplet manifold.
This subsequently enhances O[2](^1Δ[g]) singlet oxygen production.



Fig 2. Photophysics of B[18]H[22] isomers; (left) anti-B[18]H[22] isomer showing fluorescence, and
(centre) syn-B[18]H[22] isomer showing non-radiative relaxation to ground state.  Photophysics of
4,4’-(HS)[2]-anti-B[18]H[20] (right).


Other related results will also be mentioned and discussed.


References.

[1] M.G.S Londesborough, K. Lang, J. Oliva, et al., “Distinct Photophysics of the Isomers of
B[18]H[22] Explained.” Inorg. Chem. 2012, 51, 1471-1479.

[2] M.G.S Londesborough, K. Lang, J. Oliva, et al., “Tuning the Photophysical Properties of
anti-B[18]H[22]: Quantum Hopping between Excited Singlet and Triplet States in new
4,4’-(HS)[2]-anti-B[18]H[20].” Inorg. Chem. 2013, Submitted.

[3] J. Bould, M.G.S Londesborough, T. Baše, K. Lang, et al., “Reversible Capture of Small Molecules
On Bimetallaborane Clusters: Synthesis, Structural Characterization, and Photophysical Aspects.”
Inorg. Chem. 2011, 50, 7511-7523.













Michael G.S.
Londesborough                                                                           Feburary
2013