Absorption spectra, photoinduced

Figure 1. Photoinduced absorption spectrum of Y-iBaaCusOy-j (5=0.75) at 15K (2.7 eV pump at 30 mW/cm ) inset shows photoinduced spectrum of La2Cu04 obtained at 15 K (2.56 eV at 50...

Nevertheless, even for polyacetylene, the electronic structure is not that of a simple metal in which the bond-alternation and the tc-tc gap have gone to zero there are infrared active vibrational modes (IRAV) and a pseudo-gap. This is indicated by the spectra in Figure 2 which demonstrate the remarkable similarity between the doping-induced absorption found with heavily doped trans-(CH)x, and the photoinduced absorption spectrum observed in the pristine semiconductor containing a very few photoexcitations. Not only are the same IRAV mode spectral features observed, they have almost identical frequencies. 

FIGURE 5.4 Absorption, photoluminescence emission, and photoinduced absorption spectrum of a typical poly(pflrfl-phenylene)-type polymer film. The inset shows a poly(2,5-disubstituted-l,4-phenylene). 

FIGURE 5.6 Absorption, photoluminescence emission, and photoinduced absorption spectrum of a typical polyindenofluorene-type polymer film. The inset shows the actual chemical structure with R being a linear alkyl chain (from Setayesh, S., Marsitzky, D., and Mullen, K., Macromolecules, 33,2016,2000) or an aryl-substituted group (from Jacob, J., Sax, S., Piok, T, List, E.J.W., Grimsdale, A.C., and Mullen, K., /. Am. Chem. Soc., 126, 6987, 2004). 

The photoluminescence emission and absorption spectra of MeLPPP films and solutions are essentially identical [123,124] and the EL emission spectrum matches the photoluminescence spectrum. The photoluminescence quantum efficiency (tjpl) was found to he as high as 30% for pure MeLPPP [125]. The photoinduced absorption spectrum of MeLPPP exhibits two distinct features, the triplet-triplet transition from l Bu to m Ag at 1.3 eVand the polaron band at 1.9 eV. The 2.1 eV band is a vibronic replica of the 1.9 eV band. These assignments were deduced from a comparison of the PA with doping-and charge-induced absorption spectra, which only yielded the 1.9 eV bands [126]. Due to the high localization of the TE wavefiinction, the triplet band only shows a vibronic progression of 80 meV [127],... 

Fig. 10.1. The photoinduced absorption spectrum (solid curve) and linear absorption (dashed curve) of trans-polyactelyene thin film. Reprinted with permission from Z. V. Vardeny, Relaxation in Polymers, edited by T. Kobayashi, World Scientific, Singapore, 1993. Copyright 1993 by World Scientific Publishing Co. Pte. Ltd.

FIGURE 11 (a) Photoinduced absorption spectrum of PPV A7 is the change in transmission and T is the transmission through the sample, (b) Energy scheme of optical transition corresponding to the peaks in the spectrum in (a) 1101. 

Photoexcitation spectroscopy is a powerful method for studying conducting pol5mers charges are injected into the 71-electron system without chemically changing the polymer and without introducing additional disorder. Since the background absorptions are completely suppressed in the photoinduced absorption spectrum. 

The doping- and photoinduced absorption spectra of polythiophene, substituted polythiophenes, and their composites have been reported [145-166]. Let us discuss the subgap absorptions due to charged excitations in unsubstituted polythiophene. The optical absorption spectrum of BF -doped polythiophene [42,46] and the photoinduced absorption spectrum of polythiophene [145] are shown in Figure 20. In the spectrum of BFJ -doped polythiophene (Fig. 20a), doping-induced bands are observed at 0.73 and 1.68 eV, which are located below the gap edge, 1.94 eV. The 0.73-... 

Fig. 20. (a) Optical absorption spectrum of a BF -doped polythiophene film (room temperature) and (b) photoinduced absorption spectrum of a polythiophene film (20 K). 

As already indicated in Fig. 13, these IRAV modes are clearly resolved in the mid-IR region, almost joining the tail of the lower-energy mode of the two subgap transitions due to the bipolarons. More detailed structure of the IRAV modes is depicted in Fig. 14 [75] for PMT. The one-to-one correspondence between those modes induced either through doping or by photoexcitation is quite evident. Notice that because of the complete suppression of the background, much cleaner and sharper IRAV modes are found in the photoinduced absorption spectrum [75] (Fig. 14). 

Figure 8.38. Dispersion of the excited state absorption cross section (triangles) compared with the picosecond photoinduced absorption spectrum in P30T/[6,6]PCBCa (1 1).

The photoinduced absorption spectrum showed two bands at about 1.4 and 0.6 eV, features typical of positive polarons on a thiophene-based backbone. The... 

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