Langmuir and Langmuir–Blodgett films of a quinoline-fluorene based copolymer

Application of quinoline derivatives in third-generation photovoltaics

Among many chemical compounds synthesized for third-generation photovoltaic applications, quinoline derivatives have recently gained popularity. This work reviews the latest developments in the quinoline derivatives (metal complexes) for applications in the photovoltaic cells. Their properties for photovoltaic applications are detailed: absorption spectra, energy levels, and other achievements presented by the authors. We have also outlined various methods for testing the compounds for application. Finally, we present the implementation of quinoline derivatives in photovoltaic cells. Their architecture and design are described, and also, the performance for polymer solar cells and dye-synthesized solar cells was highlighted. We have described their performance and characteristics. We have also pointed out other, non-photovoltaic applications for quinoline derivatives. It has been demonstrated and described that quinoline derivatives are good materials for the emission layer of organic light-emitting diodes (OLEDs) and are also used in transistors. The compounds are also being considered as materials for biomedical applications.

Conjugated polymers as Langmuir and Langmuir-Blodgett films: Challenges and applications in nanostructured devices

Initially developed for classic systems composed of fatty acids and phospholipids, the Langmuir and Langmuir-Blodgett (LB) techniques allow the fabrication of nanometer-scale devices at self-assembly interfaces with high control over the thickness and molecular architecture. Their application in the research and production of new plastic materials has grown considerably over the past few decades due to the efficiency of conjugated polymers (CPs) for the production of light-emitting diodes, flexible displays, solar cells, and other photoelectronic devices. The structuring of polymers at different interfaces is not trivial as this class of macromolecules can undergo through different processes of folding/unfolding, which hinders the formation of stable Langmuir monolayers and, consequently, the production of Langmuir-Blodgett films. With these ideas in mind, the present article aims to review a series of elements related to the formation of stable Langmuir and Langmuir-Blodgett films of CPs, especially those based on poly(phenylene vinylene)s, polyfluorenes, and polythiophenes. This review is divided into two parts where we first discuss the formation of neat CP films, and then the strategies for the formation of stable CP films based on the co-immobilization with fatty acids, other polymers, and enzymes as mixed films.

Mechanical control of molecular aggregation and fluorescence switching/enhancement in an ultrathin film

Optical responses of molecular aggregates and assemblies are often different from that of the individual molecules. Self-assembly approaches provide little physical control on the extent of aggregation. Mechanical compression of amphiphilic molecules (with chromophore/fluorophore head groups) at the air-water interface, followed by transfer as Langmuir-Blodgett (LB) films, should prove to be an elegant route to molecular assemblies with systematically tunable aggregation and optical responses. This concept is demonstrated using monolayer LB films of a diaminodicyanoquinodimethane (DADQ)-based amphiphile fabricated at different surface pressures. Films deposited above a threshold pressure exhibit a strong blue-shift in the absorption and fluorescence relative to those deposited below; computational investigations suggest that this is due to the formation of 2-dimensional close-packed assemblies. Significantly, the blue emission of the films deposited above the threshold pressure increases with compaction, demonstrating aggregation-induced fluorescence enhancement in ultrathin films, a phenomenon well-established in crystals and nanocrystals of selected classes of molecules including the DADQs. The sharp contrast with aggregation-induced fluorescence quenching observed with most dye molecules is illustrated by a parallel investigation of LB films of a hemicyanine-based amphiphile. The present study illustrates the efficacy of simple mechanical compression and the LB technique in fabricating ultrathin films with tailored supramolecular assembly and optical responses.