touching one another, the electronic characteristics of the material may
change. For example, molecular building blocks may result in a
nanostructure in which the electrons are delocalized over the entire
aggregate. This will change the material’s optical and electronic properties, which will be determined by the shape and size of the aggregate. The
following sections provide some background in basic electronic structure
pertaining to electron delocalization and the effect of size.
5.4 SIMPLE MODELS DESCRIBING ELECTRONIC
STRUCTURE
Electrons interact with radiation, and this interaction is responsible for
the absorption and emission of radiation. Phenomena such as fluorescence, phosphorescence, and photoelectricity depend on how light
interacts with molecules. This interaction can be exploited to gain
information about molecular structure (the basis of spectroscopy).
Spectroscopy and the nature of light–matter interactions are covered in
Chapter 6. Here some pertinent elements of electronic structure are
covered. It is assumed that the student has a general chemistry level grasp
of Lewis structures, molecular orbital (MO) theory of simple molecules,
and a quantum mechanical interpretation of light (photons) and electronic structure (energy levels). A basic understanding of these processes
can be developed from the quantum mechanical models in Chapter 4.
One important equation worth recalling is Planck’s equation, which
relates energy between two energy levels (ΔE) to the wavelength (l) of
light absorbed or emitted as a result of an electronic transition between
these two energy levels (Equation 5.30):
ΔE = hv =
hc
l
(5.30)
The wavelength and frequency (n) of light is related by l = c/v, where c is
the speed of light in a vacuum (2.998 × 10
8 ms
−1 ) and h in Equation 5.24 is
Planck’s constant (6.626 × 10
−34 Js).
5.4.1 Applications of the particle-in-a-box model
Chemical reactivity and physical phenomena such as the absorption of
light is largely determined by the electronic structure in molecules. Since
electronic energy levels are quantized, Equation 5.30 provides the
CHAPTER 5: Intermolecular Interactions and Self-Assembly
164
change. For example, molecular building blocks may result in a
nanostructure in which the electrons are delocalized over the entire
aggregate. This will change the material’s optical and electronic properties, which will be determined by the shape and size of the aggregate. The
following sections provide some background in basic electronic structure
pertaining to electron delocalization and the effect of size.
5.4 SIMPLE MODELS DESCRIBING ELECTRONIC
STRUCTURE
Electrons interact with radiation, and this interaction is responsible for
the absorption and emission of radiation. Phenomena such as fluorescence, phosphorescence, and photoelectricity depend on how light
interacts with molecules. This interaction can be exploited to gain
information about molecular structure (the basis of spectroscopy).
Spectroscopy and the nature of light–matter interactions are covered in
Chapter 6. Here some pertinent elements of electronic structure are
covered. It is assumed that the student has a general chemistry level grasp
of Lewis structures, molecular orbital (MO) theory of simple molecules,
and a quantum mechanical interpretation of light (photons) and electronic structure (energy levels). A basic understanding of these processes
can be developed from the quantum mechanical models in Chapter 4.
One important equation worth recalling is Planck’s equation, which
relates energy between two energy levels (ΔE) to the wavelength (l) of
light absorbed or emitted as a result of an electronic transition between
these two energy levels (Equation 5.30):
ΔE = hv =
hc
l
(5.30)
The wavelength and frequency (n) of light is related by l = c/v, where c is
the speed of light in a vacuum (2.998 × 10
8 ms
−1 ) and h in Equation 5.24 is
Planck’s constant (6.626 × 10
−34 Js).
5.4.1 Applications of the particle-in-a-box model
Chemical reactivity and physical phenomena such as the absorption of
light is largely determined by the electronic structure in molecules. Since
electronic energy levels are quantized, Equation 5.30 provides the
CHAPTER 5: Intermolecular Interactions and Self-Assembly
164