Abstract
Electronic energy transfer and the migration of electrons generated via photoinduced electron transfer are key processes for the conversion of solar energy in natural photosynthetic systems. The proper arrangement of chromophores, electron donors and acceptors, or molecular wires on the scale of nanometers is a prerequisite for creating synthetic systems capable of achieving the high energy conversion efficiencies seen in nature. Ordered polymer layers that are adsorbed-to, or grafted-from, surfaces can serve as systems for harvesting of light and directional transfer of energy and electrons in confined environments. Moreover, ordered layers can act as templates for the desired ordering of different photoactive nanoobjects necessary for the development of optoelectronic devices, molecular electronics, and nanosensors. Herein, various macromolecular strategies are reviewed for synthesizing and arranging polymer chains on surfaces to improve the transport of electrons and excitation energy at interfaces. Specifically, the versatile layer-by-layer assembly method for forming thin films from polyelectrolytes and other charged nanoobjects, and the formation of surface-tethered polymer brushes, especially conjugated ones, with various chain architectures are presented together with their applications. The impact of various macromolecular architectures and compositions are discussed in relation to the performance of the polymer and polymer-templated films. Further development of the field could focus on precise engineering of macromolecules with complex architectures, precise positioning of active groups along the chains, towards mimicking the natural systems and their performance.
Highlights
Electronic energy transfer and the migration of electrons generated via photoinduced electron transfer are key processes for the conversion of solar energy in natural photosynthetic systems
The migration of excitation energy in polymer systems occurs via hopping from an excited chromophore to an adjacent chromophore, and can proceed either by interchain or intrachain mechanisms depending on the packing/ordering of the macromolecules [16]
The arrangement of the chromophores along the polymer chain means that they can be in close proximity even in diluted solutions, and that their separation depends on the conformation adopted by the polymer chains
Summary
For standard LbL systems, the internal structure is not wellstratified as macromolecules can diffuse between the adjacent polymer layers [73,74]. The stability and homogeneity of such prepared PEMs can be worse in comparison with those fabricated via the traditional dipping technique [85] These alternative coating methods are not always compatible with embedding chromophores into PEMs that is commonly achieved by co-adsorption with PEs during the LbL assembly [86,87,88] or by post-diffusion into the already deposited multilayers [88,89,90,91]. Drophobic aggregates, built already in the solution, was reported for such systems implying that the macromolecular structure of amphiphilic PEs must be carefully tuned to achieve an efficient entrapment of guest molecules in PEMs. LbL assembly enables structuring of films in the direction perpendicular to the substrate relying on the proper selection of the deposition sequence [35,101]. Even more complex functional PEMs may be fabricated in the future enabled by the powerful control of LbL assembly over the nanostructure and functions of the films [103]
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