1. We use a conjugated platinum containing polymer since the inclusion of platinum makes the triplet state emissive and therefore accessible via spectroscopy. The spacers R are chosen to tune the optical absorption across the whole visible spectral range. The energy gap law for triplet states in Pt-containing phenylene ethynylene polymers and monomers Joanne S. Wilson, Nazia Chawdhury, Richard Friend, Anna Köhler University of Cambridge, Cavendish Laboratory, Cambridge, United Kingdom Muna R.A. Al-Mandhary, Muhammad Khan Paul Raithby Sultan Qaboos University, Sultanate of OmanUniversity of Cambridge, Dept. of Chemistry, United Kingdom 0. Introduction References [1] D. Hertel et al., Adv. Mater.13, 65 (2001) [2] A. Köhler et al., submitted [3] R. Englman et al., J. Mol. Phys.. 18, 145, (1970) [4] W.Siebrand et al., J. Chem. Phys. 47, 2411, (1967) This work is published as J. Wilson et al., J. Am. Chem. Soc. 123, 9412, (2001) 1. Materials 3. Decay rates 4. Decay rates - results 6. Summary Polymer R = 1. 2. 3. 4. 5. 6. 7. 8. 2. Photoluminescence The relative intensity of triplet T 1 emission reduces with T 1 energy, while the singlet S 1 to triplet T 1 energy gap is constant at 0.7 eV. The lifetime  of the triplet T 1 emission reduces also with T 1 energy from 112  s to 0.2  s Experimentally,we can measure the lifetime τ T and the PL quantum yield Φ P of the triplet emission. These are related to the radiative and non-radiative decay rates k r and k nr and the efficiency of intersystem crossing Φ ISC in the following way: τ T = 1/( k r + k nr )(1) Φ P = Φ ISC k r τ T (2) Combining (1) and (2): k nr = (1-(Φ P /Φ ISC )) / τ T For these Pt-containing materials Φ ISC  1 So the non-radiative and radiative decay rates are: k r = Φ P / τ T  k nr increases exponentially with decreasing triplet energy k nr  exp (-Δ E ) At best (for Pt-polymer with T 1 at 2.4 eV) k nr  k r Non-radiative decay rates (k nr = (1-Φ P )/τ T ) Radiative decay rates (k r = Φ P / τ T ) Triplet emission in materials containing Pt-partially allowed  k r ~ 10 3 s -1 k r is determined by: k r  2 ( Δ E) 3 T1T1 S0S0 Configuration coordinate (Q) Potential energy S1S1 5. Decay Mechanism Non-radiative decay Via phonons emission By energy gap law[3,4]: k nr  exp (-γΔE /  ω) Exponential ΔE dependence  red phosphorescence is difficult to detect Large ΔE and small phonon energy  ω  low k nr Radiative decay Via dipole emission By Strickler-Berg law k r  2 ( Δ E) 3 The Triplet decay is controlled by the non-radiative mechanisms (k nr > k r ). k nr  exp (-γΔE /  ω)  High energy triplets intrinsically have the most efficient emission. Emission occurs via a multi-phonon emission process - through vibration of bonds in the material.  Control of the phonon energy  ω is needed.  Rigid materials will have less non-radiative decay. Direct phosphorescence from triplet T 1 states has now been observed in a few conjugated polymers such as polyfluorenes [1] and polyphenylene-ethynylenes [2]. But: in all these materials the triplet T 1 state is at high energy.  phosphorescence was never observed in the red spectral range. Use a model system of polymers and monomers containing Pt where the T 1 state emits. Measure phosphorescence  get decay rates of the triplet state. Relate decay rates to properties of the materials. To investigate this we: k nr = (1- Φ P ) / τ T Large ΔE  large k r Cubic ΔE dependence 10 8 10 6 10 4 10 2 10 0 k nr of T 1 k (s -1 ) k r of T 1 in Pt-polymer k r of T 1 in organic molecules k r of S 1 in organic molecules Acknowledgments The Royal Society, London, UK Peterhouse, Cambridge, UK EPSRC, UK Sultan Qaboos University, Oman Cambrige Display Technology, Cambridge, UK