Photoluminescence polymer conjugation

K.Y. Musick, Q.-S. Hu, and L. Pu, Synthesis of binaphthyl-oligothiophene copolymers with emissions of different colors systematically tuning the photoluminescence of conjugated polymers, Macromolecules, 31 2933-2942, 1998. 

Park HJ, Vak D, Noh YY, Lim B, Kim DY (2007) Surface plasmon enhanced photoluminescence of conjugated polymers. Appl Phys Lett 90 161107... 

The various functional layers in PLED devices are outlined in Figure 10.14. By applying a voltage across the device, electrons and holes are injected into the photoluminescent polymer, where they recombine to form excitons and emit light. Suitable, commonly used emissive polymers are conjugated materials such as poly(phenylenevinylene)s (PPVs) and polyfluorenes. 

FIGURE 12 Energy scheme of photoluminescence from conjugated polymers [140). 

A complete and definitive explanation of the photoluminescence spectrum observed in conjugated polymers is still under discussion and it is beyond the scope of this chapter. However, several trends in the photoluminescence of conjugated polymers are now well established and allow us to define photoluminescence criteria in order to characterize the structural order of these conjugated polymers and especially the parameters of conjugation value and dispersion of the conjugation length. 

For copolymers of structure I, for both types of side-chains, there is a striking similarity with the optical properties of the corresponding models the absorption and photoluminescence maxima of the polymers arc only 0.08-0.09 eV red-shifted relative to those of the models, as shown in Figure 16-9 (left) for the octyloxy-substituted compounds. The small shift can be readily explained by the fact that in the copolymers the chromophorcs are actually substituted by silylene units, which have a weakly electron-donating character. The shifts between absorption and luminescence maxima are exactly the same for polymers and models and the width of the emission bands is almost identical. The quantum yields are only slightly reduced in the polymers. These results confirm that the active chro-mophores are the PPV-type blocks and that the silylene unit is an efficient re-conjugation interrupter. 

The role of disorder in the photophysics of conjugated polymers has been extensively described by the work carried out in Marburg by H. Bassler and coworkers. Based on ultrafast photoluminescence (PL) (15], field-induced luminescence quenching [16J and site-selective PL excitation [17], a model for excited state thermalizalion was proposed, which considers interchain exciton migration within the inhomogenously broadened density of states. We will base part of the interpretation of our results in m-LPPP on this model, which will be discussed in some detail in Sections 8.4 and 8.6. 

Uld aviolet spectroscopy and photoluminescence are used to study the optical properties of polymers. These spectra provide information about the conjugation along die polymer backbone and the photo behavior of die polymers. 

The introduction of bulky side chains that contain adamantyl groups to poly(p-phenylenevinylene) (PPV), a semiconducting conjugated polymer, decreases the number of interchain interactions. This action will reduce the aggregation quenching and polymer photoluminescence properties would be improved [93]. 

Many of the linear conjugated tricyclic systems have interesting fluorescence or other electrophysical properties. Bis-pyrazolepyridines such as compound 30 have been incorporated into polymers as fluorescent chromophores <1999JMC339>, and used in doped polymer matrices <1997JMC2323>. They are electroluminescent at 425 nm and photoluminescent at 427 and 430 nm in a poly(vinylcarbazole) matrix with a quantum efficiency of 0.8. 

NC Greenham, IDW Samuel, GR Hayes, RT Phillips, YARR Kessener, SC Moratti, AB Holmes, and RH Friend, Measurement of absolute photoluminescence quantum efficiencies in conjugated polymers, Chem. Phys. Lett., 241 89-96, 1995. 

M. Ariu, D.G. Lidzey, M. Sims, A.J. Cadby, P.A. Lane, and D.D.C. Bradley, The effect of morphology on the temperature-dependent photoluminescence quantum efficiency of the conjugated polymer poly(9,9-dioctylfluorene), J. Phys. Condens. Matter, 14 9975-9986, 2002. 

J. Pei, W.-L. Yu, J. Ni, Y.-H. Lai, W. Huang, and A.J. Heeger, Thiophene-based conjugated polymers for light-emitting diodes effect of aryl groups on photoluminescence efficiency and redox behavior, Macromolecules, 34 7241-7248, 2001. 

M.R. Andersson, M. Berggren, T. Olinga, T. Hjertberg, O. Inganas, and O. Wennerstrom, Improved photoluminescence efficiency of films from conjugated polymers, Synth. Met., 85 1383-1384, 1997. 

As expected, the coordination of Pt markedly influences the photophysical characteristics of the PPE. The photoluminescence is efficiently quenched, and the absorption maximum in the visible regime experiences a hypsochromic shift. The charge-carrier mobility of different EHO-OPPE-Pt samples was determined by TOE measurements as described above for the neat EHO-OPPE. The shape of the photocurrent transients of all EHO-OPPE-Pt samples was similar to those shown in Figs. 6 and 7 for the neat EHO-OPPE. This indicates that these organometallic conjugated polymers networks are also characterized... 

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