Poly optical absorption

The substituted five-ring OPVs have been processed into poly crystal line thin films by vacuum deposition onto a substrate from the vapor phase. Optical absorption and photolumincscence of the films are significantly different from dilute solution spectra, which indicates that intermolecular interactions play an important role in the solid-state spectra. The molecular orientation and crystal domain size can be increased by thermal annealing of the films. This control of the microstruc-ture is essential for the use of such films in photonic devices. 

Poly(l,4-naphthylenevinylene) (106) is accessible via the Wessling polymerization procedure. Lenz, Karasz, Wegner et al. have published the synthesis of PNV 106, starting from l,4-bis(chloromethyl)naphthalene [127, 128]. The poly(l,4-naphthylenevinylene) (106) displays an optical absorption energy of 2.05 eV, slightly red-shifted by about 0,3 eV relative to the parent PPV 60-system, due to the electronic effect of the annelated benzene ring. 

As mentioned above, poly(9,10-anthrylenevinylene) is not accessible by means of the Wessling polymerization procedure. Well defined oligo(9,10-anthrylene-vinylene)s (111) were synthesized via Horner-type coupling [132]. Extrapolation of the optical absorption energies in the 111 series against the corres-... 

Figure 4.2 Comparison of UV absorption spectra of four optically active poly silanes in THF at 30°C poly methyl-(iS )-2-methylbutylsilane (1, a of 0.59), poly -hexyl-(5 )-4-methylpentyl-silane (2, a of 0.75), poly -hexyl-(5 )-3-methylpentylsilane (3, a of 0.92), and poly -hexyl-(5)-2-methyl-butylsilane (4, a of 1.25).

Figure 4.2 shows the UV absorption spectra of four optically active poly(dialkylsilane)s bearing different chiral side groups in THF at 30°C.32a It is evident that as the value of a increases from 0.59 to 1.25, the UV... 

In relation to these works, the reaction of p-nitrophenyl esters with optically active poly( propyleneimine )(8) was studied at 25°C in DMSO solution according to the same procedure described for the case of poly-L-lysine derivatives. The poly( propyleneimine ) derivatives thus obtained have different IR and UV absorption spectra from those of the starting compounds, and show absorptions assigned to the nucleic acid bases. However, their contents determined by UV spectroscopy were substantially low as compared with the case of poly-L-lysine derivatives for (9) and (20), the base contents were below 30 and 50 %, respectively. The result was explained by a steric hindrance caused by methyl groups on the main chain of poly( propyleneimine ) ... 

Optical absorption, PL and EL in poly[(tetraalkyldisilanylene)-/>-oligophenylene]s (PDSiOP) were found to depend on the length of the oligo-phenylene and not on the length of the short alkyl substituents, such as methyl and ethyl groups.76... 

Figure 2 shows the UV absorption spectra of four optically active poly (dialkylsilane)s bearing different chiral side groups in THF at 30 °C [45]. It is evident that as the value of a increases from 0.59 to 1.25, the UV absorption intensity increases, whereas the full width at half maximum (fwhm) decreases. These results led to the finding of the semi-empirical relationship between the main chain absorption characteristics and the global conformation of various polysilanes in solution. 

Figure 13 Optical absorption of the PDA poly-4BCMU in three differently ordered states (a) solution in chloroform (b) gel from toluene (dense homogeneous films cast from solution have similar, though slightly less structured, spectra) (c) single crystal.

The introduction of bridging groups on the thiophene ring modifies the physical and chemical properties of the polymers obtained. The energy of the optical absorption is reduced in FEDOT, Fig. 9.2(k), and poly(ijothia-naphthalene), (PITN) (Wudl et al., 1984), so that in the conductive state thin films are transparent. PEDOT shows high electrochemical stability in the oxidised state and, when combined with poly(styrenesulphonic acid) counter ions, can be processed from aqueous solution. 

Fig. 9.26 Temporal characteristics of photo-induced absorptions associated with charge carriers generated by short laser pulses, (a) IR absorption in MEH-PPV (reprinted from Moses et ah, 2001 copyright 2001, with permission from Elsevier) and (b) optical absorption in a poly(indenofluor-ene) (reprinted from Silva et ah, 2001 copyright 2001, with permission from Elsevier). See text for details.

Figure 4.8-2 Optical absorption of conjugated polymers with a degenerate ground state (trans-poly(acetylene)) (a), according to Suzuki et ah, 1980 and a non-degenerate ground state (poly(thiophene)) (b), according to Danno et ah, 1993 in various doping states. Doping concentrations are indicated in % in (a) and by the applied potential in (b).

One way to make the short-lived intermediates amenable to study is to increase their lifetime, usually by irradiation in the solid state and/or at very low temperatures. Then, the intermediates can be detected at the end of the irradiation by ESR or optical absorption spectroscopy. The ESR study of radicals in the solid state is done on single crystals, polycrystalline samples or frozen aqueous solution. In case of polycrystalline samples or frozen aqueous solution the identification of the radicals from the ESR spectra is difficult in many cases and, for better identification, the ESR experiment should be conducted on irradiated single crystals. Later, the method of spin trapping, developed for the liquid phase, was extended to poly crystalline solids, in this technique the polycrystalline solids are y-irradiated and subsequently dissolved in a solution containing the spin trap. 

Measuring the steady state optical absorption and emission properties of any luminescent polymer is the most basic but fundamental photophysical measurement we can make. Figure 1 depicts both the absorption and emission spectra for a series of polyfluorene oligomers and poly[9,9-di- -(2-ethylhexyljfluorene] (PF2/6), along with the fully rigid ladder type MeLPPP. 

---