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SUMMARY:Using molecular orbital arguments to explain acene-based chromopho
 re spectra - Dr Tim Hele\, University of Cambridge
DTSTART:20180208T141500Z
DTEND:20180208T151500Z
UID:TALK99277@talks.cam.ac.uk
CONTACT:Bartomeu Monserrat
DESCRIPTION:Despite considerable advances in constructing molecules which 
 absorb at particular frequencies (colours) there is a need for chromophore
 s with greater intensity of absorption (oscillator strength) for use in ap
 plications such as photovoltaics. Recent synthetic studies on the organic 
 molecules tetracene and pentacene have found some dimers and oligomers to 
 have dramatically enhanced absorption in the visible region of the spectru
 m\, whereas other dimers have spectra identical to the monomer. By combini
 ng electronic structure theory with intensity borrowing perturbation theor
 y\, here we show how this extra absorption arises from an otherwise dark c
 harge-transfer state borrowing intensity from an intense UV absorption\, a
 nd by examining the relevant molecular orbitals we explain its dependence 
 on bonding geometry. With this reasoning we construct a design rule for hi
 ghly absorbent acenes and find this solves a structure-spectrum phenomenon
  first observed seventy years ago.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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