Singlet conjugated polymers

Conjugated polymers are centrosymmetric systems where excited states have definite parity of even (A,) or odd (B ) and electric dipole transitions are allowed only between states of opposite parity. The ground state of conjugated polymers is an even parity singlet state, written as the 1A... PM spectroscopy is a linear technique probing dipole allowed one-photon transitions. Non linear spectroscopies complement these measurements as they can couple to dipole-forbidden trail-... 

In electroluminescent applications, electrons and holes are injected from opposite electrodes into the conjugated polymers to form excitons. Due to the spin symmetry, only the antisymmetric excitons known as singlets could induce fluorescent emission. The spin-symmetric excitons known as triplets could not decay radiatively to the ground state in most organic molecules [65], Spin statistics predicts that the maximum internal quantum efficiency for EL cannot exceed 25% of the PL efficiency, since the ratio of triplets to singlets is 3 1. This was confirmed by the performance data obtained from OLEDs made with fluorescent organic... 

Z Shuai, D Beljonne, RJ Silbey, and JL Bredas, Singlet and triplet excitons formation rates in conjugated polymer light-emitting diodes, Phys. Rev. Lett., 84 131-134, 2000. 

M Wohlgenannt, K Tandon, S Mazumdar, S Ramasesha, and ZV Vardeny, Formation cross-sections of singlet and triplet excitons in TT-conjugated polymers, Nature, 409 494-497, 2001. 

W Wohlgenannt, XM Jiang, C Yang, OJ Korovyanko, and ZV Vardeny, Spin-dependent polaron pair recombination in TT-conjugated polymers enhanced singlet exciton densities, Synth. Met., 139 921-924, 2003. 

A Kohler and D Beljonne, The singlet-triplet exchange energy in conjugated polymers, Adv. Funct. Mater., 14 11-18, 2004. 

---