Enhancement of charge-assisted hydrogen bond capabilities due to O-alkylation proximity in alkoxy cationic polythiophenes: solution- and solid-state evidence via EPR, AFM and surface free energy

Despite the array of applications for cationic polythiophenes (CPTs), there is still a need for structure-function guidelines and mechanistic understanding of their solution- and solid-state properties. This work presents a solution- and solid-state investigation of the effect of O-alkylation proximity on the hydrogen bonding (H-bonding) capabilities of alkoxy-CPTs, based on comparing an imidazolium alkoxy CPT with strong cation-pi, pi+ and positive charge-assisted hydrogen bonding (+CAHB) capabilities (PIMa), with two isothiouronium alkoxy CPTs with two-point +CAHB capabilities (PT1 & PT2), which have short and long alkoxy side chains, respectively. Our results show that a closer proximity of O-alkylation strengthens the +CAHB capabilities of PT1: in aqueous solutions, PT2 aggregates have a stronger interaction with cationic EPR spin probes than aggregates of PIMa and PT1, which in turn show a similar extent of repulsion towards the cationic spin probes. In solid-state, atomic force microscopy (AFM) shows that PIMa generates dendritic structures onto mica, with features of diffusion-limited aggregation (DLA), indicating strong interactions with the anionic substrate due to a high configurational entropy during spreading, regardless of being drop-casted from water or 1,4-dioxane-water (W-DI), despite the latter disturbing H-bonding due to selective solvation. PT1 is also capable of generating dendritic structures resembling ballistic aggregation (BA). However, this occurs only when casting from water, since W-DI generates island-like aggregates resembling attachment limited aggregation (ALA), which is the morphology generated by PT2 regardless of the solvent. Finally, spin-coated films of PIMa and PT1 show similar dispersivity of the surface free energy (SFE), which in turn is larger than that in PT2 films, which are also more affected when casted from W-DI, presenting much larger decreases of dispersivity. These results constitute a novel empirical structure-function guideline that could be useful for optimal design and/or processing of alkoxy CPTs. For example, dendritic patterns have recently gained attention since the colloidal droplet drying is related to engineering applications including inkjet printing, biosensing, and functional material design, while the SFE is relevant for opto- and bio-electronic applications of conjugated polyelectrolytes (CPEs). This information could also be useful when analyzing previous results obtained from alkoxy CPTs with different side chain lengths.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC’s advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

Cationic polythiophene-anionic fullerene pair in water and water-dioxane: studies on hydrogen bonding capabilities, kinetic and thermodynamic properties

Despite the vast array of solution- and solid-state bio-analytical, bioelectronic and optoelectronic applications of cationic polythiophenes (CPTs), the number of studies focused on the role of hydrogen bonding (H-bonding) between these and other molecules is scarce, regardless of whether H-bonding is expected to play an important role in several such applications. Also, despite the advantages of using cosolvents to systematically examine the molecular interactions, there are no such studies for CPTs to our knowledge. This work presents a steady-state UV-vis/fluorescence spectroscopic, kinetic and thermodynamic study on the H-bonding interactions between a water-soluble, cationic-anionic (isothiouronium-tetraphosphonate), polythiophene-fullerene donor-acceptor pair with two-point, charge-assisted H-bonding (CAHB) capabilities, tuned using water or a 1,4-dioxane-water mixture (W-DI). Both solvents generate photoinduced electron transfer (PET), fluorescence resonance energy transfer (FRET), spontaneous binding, H-bonding, ground-state complexing via multiple site binding, formation of micelle-like aggregates and equivalence points at a similar concentration of the quencher. However, in comparison with water, W-DI promotes less-ordered, less packed micellar aggregates, due to hydrophobic desolvation of the H-bond and larger solvent displacement during the PT1-4Fo complexation. This would decrease the extent of charge-transfer and the size of the sphere-of-quenching, mainly by displacements or rotations of the H-bonds, instead of elongations, together with a possible larger extent of diffusion-controlled static quenching. At [4Fo] larger than the equivalence point the micelles formed in water do not have available binding sites due to a tighter aggregation, causing a decrease in the quenching efficiency, while the micelles formed in W-DI start showing larger quenching efficiencies, possibly due to an increase in entropy that overcomes the desolvation of the H-bonding. These results could be useful when analyzing outputs from systems including CPTs with H-bonding capabilities, operating in (or casted from) solvents with clear differences in polarity and/or H-bonding capacity.

Novel benzimidazole-based conjugated polyelectrolytes: synthesis, solution photophysics and fluorescent sensing of metal ions

Two benzimidazole-based conjugated polyelectrolytes (+)-PPBIPV and (-)-PPBIPV which have opposite charges on their side chains were synthesized via Heck coupling reaction and characterized by 1H-NMR, UV-vis and PL spectroscopy. These two polyelectrolytes are both consisted of benzimidazole derivatives and phenylenevinylene units. The absorption and emission spectra reveal that the polymers both have solvent-dependency and concentration-dependency, and they exhibit aggregation effect in aqueous solution. In the respect of ion detection, the aqueous solution of (+)-PPBIPV has excellent selectivity and sensitivity for Fe3+. Moreover, Pd2+ can almost completely quench the fluorescence of (+)-PPBIPV in methanol solution, and its quenching constant KSV is 5.93×104 M-1. For (-)-PPBIPV, Sn2+ can double the fluorescence intensity of its aqueous solution, while (-)-PPBIPV has good identification for Fe3+ in methanol with a KSV = 3.44×105 M-1. Hence, two polyelectrolytes have considerable potential to become effective fluorescent sensing materials for some specific metal ions. All of the stoichiometric relationships between metal ions and conjugated polyelectrolytes were calculated using Benesi-Hildebrand equation.

Reversible Hydrogen Releasing and Fixing with Poly(Vinylfluorenol) through a Mild Ir-Catalyzed Dehydrogenation and Electrochemical Hydrogenation

The radical polymerization of 2-vinylfluorenol, an alcohol derivative of vinylfluorene, gives poly(vinylfluorenol), which quantitatively releases hydrogen gas (≈110 mL per gram polymer at standard temperature and pressure) by simply warming at 100 °C with an iridium catalyst. A high population of fluorenol units in the polymer accomplishes a large formula-weight-based theoretical hydrogen density (1.0 wt%). The dehydrogenated ketone derivative, poly(vinylfluorenone), exhibits reversible negative-charge storage with a high density of 260 mAh g^-1 . The electrolytically reduced poly(vinylfluorenone) is momentarily hydrogenated in the presence of an electrolyte with water as the hydrogen source to be converted to the original poly(vinylfluorenol). The formed poly(vinylfluorenol) almost quantitatively evolves hydrogen gas similar to the starting poly(vinylfluorenol). Both hydrogen and charge storage with the organic fluorenol/fluorenone polymer suggest a new type of energy-storage configuration.

Self-assembly and chiroptical properties in supramolecular complexes of adenosine phosphates and guanidinium-bispyrene

Supramolecular systems that respond to the hydrolysis of adenosine phosphates (APs) are attractive for biosensing and to fabricate bioinspired self-assembled materials. Here, we report on the formation of supramolecular complexes between an achiral guanidinium derivative bearing two pyrene moieties, with each of the three adenosine phosphates: AMP, ADP, and ATP. By combining results from circular dichroism spectroscopy and molecular modeling simulations, we explore the induced chirality, the dynamics of the complexes, and the interactions at play, which altogether provide insights into the supramolecular self-assembly between APs and the guanidinium-bispyrene. Finally, we identify the chiroptical signals of interest in mixtures of the guanidinium derivative with the three APs in different proportions. This study constitutes a basis to evolve toward a chiroptical detection of the hydrolysis of APs based on organic supramolecular probes.