Conducting polymers electronic wave functions

Undoped conjugated polymers have an anisotropic, quasi-one-dimensional electronic structure with the tt electrons coupled to the polymer backbone via electron-phonon interactions. The overlapping of TT- (also TT -) electron wave functions forms a valence band (conduction band) with a gap size of typically 2-4 eV, corresponding to the conventional semiconductor gap. As a result, undoped conjugated polymers (hereafter called simply semiconducting polymers) exhibit the electronic and optical properties of semiconductors in combination with the mechanical properties of general polymers, making them potentially useful for a wide array of applications. [Pg.78]

When the concentration of chain interruptions is sufficiently high such that the left hand side of equation 1.3 is small, then the wave function will be localised. The possible limits for the conductivity arise from the chain interruptions and/or phonon scattering. All the above factors suggest that in high-quality conducting polymers the electronic mean free path could be much larger than the structural coherence length and real metallic features could be observed. [Pg.21]

The ao value depends on the electron-phonon-coupling constant, while Tq is in connection with the localized density of states near the Fermi level and the decay length of the wave function, respectively. It can be seen that conductivity increases with temperature in contrast to that of the metals. This type of conductivity behavior has been verified for many conjugated polymer systems. The problem of locaKzation is less important if the molar mass of the polymer is high and only a few defects are present, as well as a relatively intense interchain coupKng prevails. In... [Pg.5916]

Since this section is intended to investigate the optical properties of conducting polymers, it is relevant to review some basic optical properties of simple solids. Therefore, this section starts with a rather elementary treatment of the optical constants. The optical constants of solids provide information on their electronic and vibronic structure since the electromagnetic field of the light wave interacts with all fixed and mobile charges [1171,1172]. For a simple solid (a homogeneous, isotropic, and linear medium that is local in its response), the response of the system to the field is characterized by a complex dielectric function, e(o)), given as... [Pg.63]

Functional polymers may be used for dihierent types of chemical sensors, including acoustic wave sensors (bulk acoustic wave, surface acoustic wave, and flexural plate wave sensors), electronic conductance sensors (semiconducting and capacitance sensors), and calorimetric sensors. ... [Pg.12]