Controversy over physical properties

Conjugated polymers, in the undoped state, 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 particularly in organic optoelectronic devices such as polymer LEDs, photodetectors, photovoltaic cells, etc. Development in the performance of such devices has advanced rapidly, and prototype devices now meet realistic specifications for practical applications. In spite of such successful achievements in the scope of device application, however, there is still controversy over the nature of the electronic structure and the appropriate description of the underlying physics of elementary excitations. Since these issues are both scientifically interesting and critically important to the assessment of the future potential of devices based on conjugated polymers, more detailed... 

The Lewis-type (L) contribution is considered the easy part of chemical wavefunction analysis, because it corresponds closely to the elementary Lewis structure model of freshman chemistry. Nevertheless, controversy often arises over the magnitude of steric or electrostatic effects that are associated with the Lewis model itself [i.e., distinct from the resonance-type effects contained in (NL)]. The NBO program offers useful tools for quantifying both steric and electrostatic interactions in terms of the space-filling (size and shape) and dielectric properties (charge, dipole moment, etc.) of the electron pair bonds and lone pairs that comprise the Lewis structure model. This chapter discusses the physical nature and numerical quantitation of these important chemical effects, which are often invoked in a hand-waving manner that reflects (and promotes) significant misconceptions. 

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