Lifetimes luminescent conjugated polymers

The disadvantages of organic dyes (low photostability, insufficient brightness, short lifetimes, etc.) have resulted in competition from luminescent metal-ligand complexes, semiconductor nanoparticles (Quantum Dots), and conjugated polymers. These new materials show advanced performance in a variety of applications... 

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

Time-resolved photoluminescence spectroscopy has emerged as one of the most important tools for studying the properties of solid-state materials suited to optoelectronic applications, including semiconducting polymers. This is due to the relatively direct information about the excitation dynamics, such as recombination and relaxation processes, which is obtained from such experiments. Wong et al. [1232] have reported a luminescence lifetime much smaller than 1 ns in conjugated polymers and have pointed out that nonradiative as well as bimolecular processes might play an important role. Furukawa et al. [1233] have studied time-resolved luminescence in PPV and have explained the re-... 

The ground state of most of the luminescent molecules and polymers which are used as the emitters in OLEDs and PLEDs is the symmetric singlet 11 Ag state.22 Figure 1.4 shows thebasic processes which may occur following photoexcitation of the molecule or conjugated segment of the polymer. Since the material is assumed to be luminescent, the antisymmetric 11 Bu state must lie below the symmetric 2-photon 21 Ag state. Otherwise, photoexcitation will still populate the 11 Bu state, but that state will quickly decay to the 21 Ag, and the latter will decay nonradiatively to the ground state, with lifetimes as short as 2 ps.23... 

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