BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Non-radiative processes in organic semiconductors&quot\;  - Dr Jen
 ny Clark\, Optoelectronics\, Cavendish
DTSTART:20130204T140000Z
DTEND:20130204T150000Z
UID:TALK43410@talks.cam.ac.uk
CONTACT:Leona Hope-Coles
DESCRIPTION:Non-radiative deactivation of neutral excited states in organi
 c semiconductors can determine the overall efficiency of devices such as s
 olar cells or lasers. For energy harvesting in solar cells\, for example\,
  ultrafast non-radiative multiexciton generation through ‘singlet fissio
 n’ could prove fundamental for future increases in efficiency. On the ot
 her hand\, in organic semiconductor lasers\, all non-radiative processes s
 hould be avoided and high photoluminescence\n(PL) quantum efficiencies are
  required.\n\nAs an example of my work\, I will present a spectroscopic st
 udy of two non-radiative processes in conjugated polymers. The first demon
 strates how internal conversion is coupled with molecular conformational r
 eorganization. In general\, conformational change occurs on a timescale de
 fined by the energy of the main vibrational mode and the rate of energy di
 ssipation. Typically\, for a conformational change such as a twist around 
 the backbone of a conjugated molecule\, this occurs on the tens of picosec
 onds timescale. However\, I will demonstrate that in certain circumstances
  the molecule\, in this case an oligofluorene\, can change conformation ov
 er two orders of magnitude faster (that is sub-100 fs) in a manner analogo
 us to inertial solvent reorganization demonstrated in the 1990s. Theoretic
 al simulations demonstrate that non-adiabatic transitions during internal 
 conversion can efficiently convert electronic potential energy into torsio
 nal kinetic energy\, providing the ‘kick’ that prompts sub-100 fs tors
 ional reorganization.\n\nThe second example is of singlet fission in a con
 jugated polymer.\nSinglet fission is a spin-allowed process in organic sem
 iconductors whereby a singlet exciton separates into two spatially distinc
 t triplet excitons. Singlet fission has been recently extensive studied in
  small molecule systems such as pentacene owing to its potential for solar
  cells. Unfortunately in these systems\, singlet fission efficiency is hig
 hly dependent on intermolecular packing\, making implementation in solar c
 ells problematic. To overcome this problem\, we demonstrate intrachain sin
 glet fission in the solution-processable and stable conjugated polymer pol
 y(thienylene-vinylene). I will discuss the mechanism of singlet fission in
  this polymer and the potential for its use as a sensitizer.\n
LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory\, Department of Ph
 ysics
END:VEVENT
END:VCALENDAR