Absorption maxima orientation effect

Film preparation plays a crucial role in determining the photoelectrochemical properties of phthalocyanine electrodes. Since the coupling of individual chro-mophores strongly depends on their relative orientation, the position of the absorption maximum and its width show a clear dependence on the structure of thin films. Also, charge transport within phthalocyanine films, a fundamental necessity for the films to work as electrodes, depends upon the overlap of the frontier orbital wave functions which is also dependent on intermolecular orientation. Beyond the microscopic structure of films the morphology of films plays an important role. In the case of crystalline films, the orientation of crystallites relative to the electrode surface will be relevant because of anisotropies in optical absorption and charge transport. The size of the observed photocurrent direcdy depends on the effective electrode surface area accessible by the electrolyte and this leads to a strong dependence on the porosity of the films. 

IR spectroscopy is not only useful for determining the chemical constitution of polymers. It additionally provides profound information on chain orientation and on the orientation of attached lateral substituents of polymers. In this case, polarized IR radiation is applied which is only absorbed by an IR-active bond if the plane in which the electrical field vector E of the IR beam oscillates is parallel to the transition dipole moment p of the vibration to be excited. If, on the other hand, the transition dipole moment p is perpendicular to the electrical field vector E of the IR beam no absorption is observed. Using this effect, the degree of orientation of a polymer sample (film, fiber) can be estimated by comparing the intensity at maximum /(11) and at minimum I ) absorption, i.e., the dichroic ratio. 

The depth of any reasonable potential well should of course be finite. Moreover, the recorded spectrum of such an important liquid as water comprises two absorption bands One, rather narrow, is placed near the frequency 200 cm, and another, wide and intense band, is situated around the frequency 500 or 700 cm-1, for heavy or ordinary water, respectively. In view of the rules (56) and (57), such an effect can arise due to dipoles reorientation of two types, each being characterized by its maximum angular deflection from the equilibrium orientation of a dipole moment.20 The simplest geometrically model potential satisfying this condition is the rectangular potential with finite well depth, entitled hat-flat (HF), since its form resembles a hat. We shall demonstrate in Section VII that the HF model could be used for a qualitative description of wideband spectra recorded in water21 and in a nonassociated liquid. 

Photoluminescence (PL) experiments were performed on methylstilbene-equipped peptides (Aib-Stb-D and Aib-Stb-O) in TFE to assess the effect of the relative orientation of electroactive side chains on their electronic properties. Aib-Stb-D and Aib-Stb-O show identical absorption spectra (data not shown) and display monomeric methylstilbene emission with a peak maximum at 357 nm (Figure 6) however, they exhibit notably different PL intensities. Aib-Stb-O... 

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