Poly absorption spectra

The absorption spectrum of poly(2-methoxy-5-(2 -ethyI-hexyIoxy)-/mra-phenyIene vinylene) (MEH-PPV) is shown in Figure 7-8a. Phcnylene-based conducting polymers such as MEH-PPV exhibit multiple absorption features extending well into... 

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

Fig. 22. Dependence of the absorption spectrum of P/3DMP-C104 (poly-/i-dimethyl pyrrole) on the reducing potentials. The voltages written in the figure are the applied voltages between the working and counter electrodes. The numbers in parentheses are the molecular ratios of the perchlorate ion to a pyrrole ring. Each spectrum is obtained using a different free standing film which has almost the same thickness as the others. Reproduced from [377].

Fig.7. Quadratic Stark effect spectrum of a poly(methylmetacrylate) film doped with an azobenzene-linked amphiphile C180AZ0C00H (solid line). Dotted line, broken line, and dash and dotted line show an absorption spectrum of the film, its first derivative, and second derivative, respectively.

Figure 13. Absorption spectrum of a 1 im thick poly(styrene) film on a quartz disc.

Figure 3. Typical UV absorption spectrum of D " or D "/D blend or a poly(dimethyl-diphenyl)siloxane oligomer (CHCl solution)...

The delocalization of the conduction electron onto the side chains would be expected if the pendant groups were replaced with more electrophilic substituents than the phenyl group. However, this is not the case. Figure 22 shows the absorption spectrum of poly-(methylnaphthylsilane) radical anion. The absorption spectrum is very similar to that of the naphthalene radical anion, which implies that the unpaired electron is localized on the pendant group. Increase of the electron affinity of pendant groups does not necessarily cause the delocalization. 

Replacing all the pendant groups with aryl groups attains the delocalization of the unpaired electron. Figure 23 compares the absorption spectra of the radical anions of poly-(4-ethylphenyl-phenylsilane) and poly(dicyclohexylsilane) in MTHF at 77 K. Although the molecular structures of these polysilanes are similar, the absorption spectra are different. The absorption spectrum of the poly(dicyclohexylsilane) radical anions is similar to that of... 

The close correspondence of the DNA absorption spectrum with that of a mixture of mononucleotides of the same composition illustrates the weak nature of the interactions between neighboring purine and pyrimidine bases guanine (G), cytosine (C), adenine (A), and thymine (T) at an interplanar separation of 3.36 A in the unexcited double-helical configuration. On the other hand the structureless fluorescence band of (calf-thymus) DNA is red-shifted by 3500 cm-1 from the fluorescence spectral origin of the mononucleotides it closely resembles the fluorescence spectrum of the dinocleotide ApT (and of poly dAT) and is accordingly identified131 with the fluorescence... 

Finally, two related studies can be mentioned here. It was noted that when a quartz plate was immersed overnight in a solution of Pb(C104)2 and poly(vinyl alcohol) through which H2S had been bubbled, a film formed on the plate parallel with formation of a colloidal PbS sol [47]. The film was extremely thin (maximum absorbance of <0.015 at 400 nm). The absorption spectrum of this film was similar to that of the PbS sol and consisted of several absorption peaks with an absorption onset of ca. 630 nm (1.97 eV). It is not clear that this is the true bandgap onset, for the same reasons as discussed previously (weak absorption close to the bandgap). The XRD crystal size of the precipitate was ca. 3 nm. 

Figure 14.1. Visible-near-IR absorption spectrum of poly(methylmethacrylate) (PMMA) dissolved in...

Studies of the triplet-triplet absorption spectrum of P1VN 59) and P2VN 60-61> in degassed fluid solution have shown that triplet annihilation is still important at room temperature. The triplet absorbance of dilute poly(vinylnaphthalene) solutions is only 0.05-0.2 times as large as that of the corresponding ethylnaphthalene solution having the same concentration of naphthyl groups. While quantitative data on kMXX at room temperature are unavailable, the ordinary triplet decay rate kx has been extensively studied for monochromophoric compounds. 

Fig. 1. Normalized absorption and corrected emission spectra for poly (A) and poly(dA) in aqueous solution at neutral pH. The normalized absorption spectrum of AMP is presented for comparison.

The steady state absorption and emission spectra of poly(A), poly(dA), and the absorption spectrum of the ribonucleotide monomer adenosine 5 -monophosphate (AMP) are shown in Fig. 1. The absorption spectra of poly(A) and poly(dA) are essentially identical. The AMP absorption spectrum is similar to the polymer spectra, but subtle differences exist. The absorption maximum of both homopolymers is shifted to the blue by several hundred wavenumbers, while the low energy band edge is red-shifted with respect to AMP. Similar shifts are observed at 77 K [15]. 

Fig. 11 Illustration of the excited state relaxation derived from experimental results obtained for poly(dA).poly(dT) by steady-state absorption and fluorescence spectroscopy, fluorescence upconversion and based on the modeling of the Franck-Condon excited states of (dA)io(dT)io. In red (full line) experimental absorption spectrum yellow circles arranged at thirty steps represent the eigenstates, each circle being associated with a different helix conformation and chromophore vibrations.

Poly(2,5-silole) 7 shows a Aab of 482 nm at room temperature.24 A band gap of the polymer, if calculated with the absorption edge (650 nm), is 1.9 eV. A silole-thiophene alternating copolymer 8 can show a further decreased band gap.25 The copolymer displays a broad absorption spectrum with Aab at 648 nm in chloroform. The calculated band gap from the absorption edge is only 1.55 eV, a very small value so far reported for the synthesized SCPs. 

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