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SUMMARY:How bonding topology affects polyacene spectra: design principles 
 for singlet fission chromophores - Timothy Hele
DTSTART:20160527T110000Z
DTEND:20160527T114000Z
UID:TALK65670@talks.cam.ac.uk
CONTACT:Alex Thom
DESCRIPTION:Polyacene molecules such as pentacene and tetracene as well as
  their dimers and oligomers have considerable potential in molecular elect
 ronic devices and to improve the efficiency of photovoltaic cells. Recent 
 experimental research has found that bonding monomers via a carbon at the 
 ‘end’ of a polyacene\, rather than one along the ‘top’ or ‘botto
 m’ leads to the second peak in the electronic spectrum to be hugely enla
 rged and redshifted - enough to change the molecule’s colour to the nake
 d eye. Furthermore\, Pople-Parr-Pariser (PPP) theory\, a more sophisticate
 d version of Huckel theory commonly used to investigate alkene spectra\, p
 redicts this intense transition to be forbidden. Using tools ranging from 
 simple molecular orbital theory to multireference electronic structure cal
 culations and quantum mechanical group theory\, we show that this transiti
 on is to a highly multiconfigurational excited state whose intense transit
 ion dipole moment results from a breakdown of the neglect of differential 
 overlap assumption in PPP Theory. These results illustrate the need for hi
 ghly multireference electronic structure calculations\, elucidate the limi
 ts of Huckel Theory and provide widely-applicable design rules for polyace
 ne chromophores.\n
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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