by the presence of non-equivalent isomorphic substitutions in the structure.
Graphene or chalcogenides are typical examples of materials based on particles
with no original surface charge. They need to be modified or functionalized to get
them to disperse in polar solvents. The charge of some materials can be induced by
redox reactions or by protolytic reactions.
4.2 Layered Nanoparticles as the Hosts of Dye Molecules
and FRET
Hybrid materials consisting of organic dyes and layered hosts are, at first sight, a
relatively well-defined group of systems and materials. In fact, these materials can be
very diverse in terms of the combination of an almost infinite number of types of
substances. The variability could be even higher when considering structurally
different variants of the materials based on the same components. The presence of
other substances, which are often included to stabilize the systems and to preserve
the photoactivity of the dyes, opens up further possibilities for the preparation of
very diverse ternary, multicomponent, and very complex hybrid materials. These
hybrid systems include various types ranging from colloids, through solid materials,
thin films to nanocomposites with polymers. The photoactive component, which is
represented by organic dyes, can be in the form of neutral molecules or ions of
conventional dyes, but also luminophore-labeled surfactant molecules, luminescent
polymeric substances, biopolymers, and conventional polymers labeled with
luminophores. Inorganic components can be represented by photochemically inactive particles or by the properties of semiconductors, conductors, and luminescent
materials. Depending on the nature of an organic dye, different types of adsorption
and interactions between the components occur. In addition to most frequent electrostatic interactions, covalent and coordination bonds can be applied to attach
fluorophore groups onto the particles. In some cases, van der Waals forces and
hydrogen bonding significantly contribute to the binding of organic dyes in specific
materials.
4.2.1 Complexes with Ionic Dyes
The most frequent type of hybrid system is based on charged nanoparticles that are
counterbalanced by organic ions with an opposite charge. The organic dyes may
include ionic chromophores or molecules modified with ionic groups. An example
of the latter type is derivatives of neutral dyes modified with alkylamine groups,
which hydrolyze to form positively charged species [21]. To date, many papers on
complexes of layered silicates with cationic dyes have been published and reviewed
[5, 7, 13, 14, 22–24]. An opposite example in terms of the charge of the individual
components is LDH systems with positively charged layers and anionic dyes
[25, 26]. The main advantages of using ionic dyes are their relatively good solubility
216
J. Bujdák
Graphene or chalcogenides are typical examples of materials based on particles
with no original surface charge. They need to be modified or functionalized to get
them to disperse in polar solvents. The charge of some materials can be induced by
redox reactions or by protolytic reactions.
4.2 Layered Nanoparticles as the Hosts of Dye Molecules
and FRET
Hybrid materials consisting of organic dyes and layered hosts are, at first sight, a
relatively well-defined group of systems and materials. In fact, these materials can be
very diverse in terms of the combination of an almost infinite number of types of
substances. The variability could be even higher when considering structurally
different variants of the materials based on the same components. The presence of
other substances, which are often included to stabilize the systems and to preserve
the photoactivity of the dyes, opens up further possibilities for the preparation of
very diverse ternary, multicomponent, and very complex hybrid materials. These
hybrid systems include various types ranging from colloids, through solid materials,
thin films to nanocomposites with polymers. The photoactive component, which is
represented by organic dyes, can be in the form of neutral molecules or ions of
conventional dyes, but also luminophore-labeled surfactant molecules, luminescent
polymeric substances, biopolymers, and conventional polymers labeled with
luminophores. Inorganic components can be represented by photochemically inactive particles or by the properties of semiconductors, conductors, and luminescent
materials. Depending on the nature of an organic dye, different types of adsorption
and interactions between the components occur. In addition to most frequent electrostatic interactions, covalent and coordination bonds can be applied to attach
fluorophore groups onto the particles. In some cases, van der Waals forces and
hydrogen bonding significantly contribute to the binding of organic dyes in specific
materials.
4.2.1 Complexes with Ionic Dyes
The most frequent type of hybrid system is based on charged nanoparticles that are
counterbalanced by organic ions with an opposite charge. The organic dyes may
include ionic chromophores or molecules modified with ionic groups. An example
of the latter type is derivatives of neutral dyes modified with alkylamine groups,
which hydrolyze to form positively charged species [21]. To date, many papers on
complexes of layered silicates with cationic dyes have been published and reviewed
[5, 7, 13, 14, 22–24]. An opposite example in terms of the charge of the individual
components is LDH systems with positively charged layers and anionic dyes
[25, 26]. The main advantages of using ionic dyes are their relatively good solubility
216
J. Bujdák