Photoluminescence emission quantum yields

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 solution photoluminescence quantum yields of the copolymers are high (0.4-0.8) and indicate a great potential in light emission applications [60, 64-69],... 

All the emission spectra in solution showed a maximum peak with a shoulder on the red side. It was observed that the photoluminescence A.max in dilute THF solution red shifted from 470 to 474. They also exhibited similar Stokes shifts (about 66 nm) due to their similar backbone. The fluorescence quantum yields ( F) of these molecular wires in dilute THF solution were measured to be 0.25 for 470,0.22 for 471,0.20 for 472,0.20 for 473, and 0.18 for 474, respectively. The excited-state lifetime for OTEs was found to be single-exponential within a few hundred picoseconds. However, in THF solution (10 17 M), the decay of the emission maximum band for these molecular wires was found to be biexponential with two excited-state lifetimes yielding a c2 of <1.2. One excited-state lifetime ranged from 0.42 to 0.30 ns, which was in agreement with that in OTEs. Another one exhibited a... 

All the copolymers showed similar absorptions with Lmax at 470 nm, which was more intense for polymers with higher thiophene content. In contrast, their emission colors were progressively red shifted with increasing thiophene-based comonomer content. Copolymer 596a emitted bright red light (620 nm) with reasonably high photoluminescent quantum yields (34-69%). 

Many important photophysical properties, such as aggregation-induced emission (AIE),11,12 blue shift of PL emission in the crystal state relative to that of amorphous solid,13 extremely high photoluminescence (PL) quantum yields... 

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