17 Azulene-Based Materials for Organic Field-Effect Transistors
343
Fig. 17.2 Frontier orbitals of azulene and naphthalene calculated at the B3LYP/6-31G(d) level of
theory
17.2.2 The Molecular Structure of an Ideal OFET Material
Organic crystalline materials based on π-conjugated compounds are typically used in
OFETs, and a highly ordered molecular arrangement is required in the crystalline thin
film of the active layer in order to realize high performance. As a result, planar and
linear structural extensions have been widely used to increase dispersion forces by
extending the π-electron system. In many cases, molecules with rigid planar structures show end-on orientations perpendicular to the substrate, which makes them
suitable for use in typical lateral FET devices that conduct current in the planes of
their organic thin films [15–17]. In particular, two-dimensional herringbone structures with edge-to-face configurations, such as pentacene, are representative highperformance organic transistor materials. The crystal structures of these polycyclic
aromatic hydrocarbons have been systematically summarized, with these compounds
widely recognized as having long and narrow molecular shapes and large aspect ratios
(Fig. 17.3) [18, 19]. In order to obtain a molecular structure with a large aspect ratio,
it is desirable to extend the structure of azulene at its 2- and 6-positions.
343
Fig. 17.2 Frontier orbitals of azulene and naphthalene calculated at the B3LYP/6-31G(d) level of
theory
17.2.2 The Molecular Structure of an Ideal OFET Material
Organic crystalline materials based on π-conjugated compounds are typically used in
OFETs, and a highly ordered molecular arrangement is required in the crystalline thin
film of the active layer in order to realize high performance. As a result, planar and
linear structural extensions have been widely used to increase dispersion forces by
extending the π-electron system. In many cases, molecules with rigid planar structures show end-on orientations perpendicular to the substrate, which makes them
suitable for use in typical lateral FET devices that conduct current in the planes of
their organic thin films [15–17]. In particular, two-dimensional herringbone structures with edge-to-face configurations, such as pentacene, are representative highperformance organic transistor materials. The crystal structures of these polycyclic
aromatic hydrocarbons have been systematically summarized, with these compounds
widely recognized as having long and narrow molecular shapes and large aspect ratios
(Fig. 17.3) [18, 19]. In order to obtain a molecular structure with a large aspect ratio,
it is desirable to extend the structure of azulene at its 2- and 6-positions.