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The design and characterization of discrete self-assembly of specific hydrogen-bonded dyads based on diaminopyridine (DAP) and flavin are described. The combination of the same stereocenters on both recognition units has provided cooperative self-assembly resulting in improvement of stability and efficient chiroptical switching.

A combination of theoretical calculations and spectroscopic techniques is used to investigate two distinctive driving forces in hydrogen bond formation, which compete in two chemically related receptors. The results of the investigation are being applied to rationally design improved host systems for biomimetic experiments and electroactive devices.

A biologically inspired polymer was created with a three-dimensional structure provided by hydrogen bond-mediated folding. The strategy was applied to site isolation of and electroactive guest in the core of a globular polymer.

The synthesis of a new family of receptors for flavins based on 6-aryl-2,4-(acyldiamino)-s-triazines is described. The scheme involves the reaction of the corresponding nitriles with dicyandiamide and potassium hydroxide to form diaminotriazines, which yields the corresponding receptors after acylaton with isobutyryl chloride. The conditions and mechanisms for the reactions are presented.

The formation of micelles from a tetrathiafulvalene (TTF) end-functionalized poly(N-isopropylacrylamide) (poly(NIPAM)) derivative is described. The studies have shown that the chemical oxidation and complexation properties of the TTF unit are used for disrupting the micelle architecture to release the hydrophobic dye Nile Red from the interior of the micelle.

A switchable organic system involving four distinct states is developed, which can be interconverted by using both pH and redox chemistry as control parameters. The results have shown that the pH-modulated cyclization and phase-transfer process between the 1-isobutyl-1,2,3,12b-tetrahydroimidazo[1,2-f]phenanthridine (TIP) and 5-[2-(isobutylamino)ethyl]phenanthridinium (AEP) states is quantitative and repeatable without any major loss in activity and that the reduction or oxidation might be used for locking out these states against acid-base-induced changes.

A complimentary polytopic interaction method to improve applicable properties of discotic liquid crystals is proposed.

The use of the corresponding acid fluoride from chlorocarbonylferrocene as a synthetic intermediate in the synthesis of ferrocenyl esters and amides was investigated. The results showed that the generation of the acid fluoride occurred under mild conditions and proceeded with a high level of functional group compatibility. Reactions with alcohol were observed to be sluggish, even in the presence of excess alcohol. Overall, fluorocarbonylferrocene proved to be a useful and versatile synthetic intermediate for the formation of amides and esters.

A series of flavins were synthesized bearing electron-withdrawing and -donating substituents. The electrochemical properties of these flavins in a nonpolar solvent were determined. The recognition of these flavins by a diamidopyridine (DAP) receptor and the effect this receptor has on flavin redox potential was also quantified. It was found that the DAP-flavin binding affinity and the reduction potentials (E[SUB1/2]) for both the DAP-bound and unbound flavins correlated well with functions derived from linear free energy relationships (LFERS). These results provide insight and predictive capability for the interplay of electronics and redox State-Specific interactions for both abiotic and enzymatic systems. [ABSTRACT FROM AUTHOR]

Good selective contacts are necessary for solar cells that are efficient and have long-term stability. Since 1998, with the advent of solid-state dye sensitized solar cells (DSSC), Spiro-OMeTAD has become the reference hole-transporting material. Yet, for efficient solar cells Spiro-OMeTAD must be partially oxidized with chemical dopants, which compromises the long-term stability of the solar cell. Alternatively, semiconductor polymers such as PTAA have been also studied, matching or improving the solar cell characteristics. However, PTAA -based devices lack long-term stability. Moreover, both Spiro-OMeTAD and PTAA are expensive materials to synthesize. Hence, approaches toward increasing the solar cell stability without compromising the device efficiency and decreasing the manufacturing cost are very desirable. In this work we have modified Spiro-OMeTAD , by an easy-to-use methodology, by introducing a carboxylic acid anchoring group ( Spiro-Acid ), thereby allowing the formation of self-assembled monolayers (SAMs) of the hole-transporting material in dopant-free p-i-n hybrid perovskite solar cells (iPSCs). The resulting device showed a champion efficiency of 18.15% with ultralow energy loss, which is the highest efficiency among Spiro-OMeTAD -based iPSCs, and a remarkable fill factor of over 82%, as well as excellent long-term illumination stability. Charge transfer and charge carrier dynamics are studied by using advanced transient techniques to understand the interfacial kinetics. Our results demonstrate that the Spiro-OMeTAD -based SAMs have a great potential in producing low-cost iPSC devices, due to lower material usage, good long-term stability, and high performance., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

With the increased application of batteries in powering electric vehicles as well as potential contributions to utility-scale storage, there remains a need to identify and develop efficient and sustainable active materials for use in lithium (Li)- and sodium (Na)-ion batteries. Organic cathode materials provide a desirable alternative to inorganic counterparts, which often come with harmful environmental impact and supply chain uncertainties. Organic materials afford a sustainable route to active electrodes that also enable fine-tuning of electrochemical potentials through structural design. Here, we report a bis-anthraquinone-functionalized s-indacene-1,3,5,7(2H,6H)-tetraone ( BAQIT ) synthesized using a facile and inexpensive route as a high-capacity cathode material for use in Li- and Na-ion batteries. BAQIT provides multiple binding sites for Li- and Na-ions, while maintaining low solubility in commercial organic electrolytes. Electrochemical Li-ion cells demonstrate excellent stability with discharge capacities above 190 mAh g -1 after 300 cycles at a 0.1C rate. The material also displayed excellent high-rate performance with a reversible capacity of 142 mAh g -1 achieved at a 10C rate. This material affords high power capabilities superior to current state-of-the-art organic cathode materials, with values reaching 5.09 kW kg -1 . The Na-ion performance was also evaluated, exhibiting reversible capacities of 130 mAh g -1 after 90 cycles at a 0.1C rate. This work offers a structural design to encourage versatile, high-power, and long cycle-life electrochemical energy-storage materials., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Additives play an important role in modifying the morphology and phase separation of donor and acceptor molecules in bulk heterojunction (BHJ) solar cells. Here, we report triptycene (TPC) as a small-molecule additive for supramolecular control of phase separation and concomitant improvement of the power conversion efficiency (PCE) of PTB7 donor and fullerene acceptor-based BHJ polymer solar cells. An overall 60% improvement in PCE is observed for both PTB7:PC 61 BM and PTB7:PC 71 BM blends. The improved photovoltaic (PV) performance can be attributed to three factors: (a) TPC-induced supramolecular interactions with donor:acceptor components in the blends to realize a nanoscale phase-separated morphology; (b) an increase in the charge transfer state energy that lowers the driving force for electron transfer from donor to acceptor molecules; and (c) an increase in the charge carrier mobility. An improvement in efficiency using TPC as a supramolecular additive has also been demonstrated for other BHJ blends such as PBDB-T:PC 71 BM and P3HT:PCBM, implying the wide applicability of this new additive molecule. A comparison of the photostability of TPC as an additive for PTB7:PCBM solar cells to that of the widely used 1,8-diiodooctane additive shows ∼30% higher retention of PV performance for the TPC-added solar cells after 34 h of AM 1.5G illumination. The results obtained suggest that the approach of using additives that can promote supramolecular interactions to modify the length scale of phase separation between donor and acceptor is very promising and can lead to the development of highly efficient and stable organic photovoltaics.

The structure adopted by biomaterials, such as proteins, at interfaces is a crucial parameter in a range of important biological problems. It is a critical property in defining the functionality of cell/bacterial membranes and biofilms (i.e., in antibiotic-resistant infections) and the exploitation of immobilized enzymes in biocatalysis. The intrinsically small quantities of materials at interfaces precludes the application of conventional spectroscopic phenomena routinely used for (bio)structural analysis due to a lack of sensitivity. We show that the interaction of proteins with superchiral fields induces asymmetric changes in retardation phase effects of excited bright and dark modes of a chiral plasmonic nanostructure. Phase retardations are obtained by a simple procedure, which involves fitting the line shape of resonances in the reflectance spectra. These interference effects provide fingerprints that are an incisive probe of the structure of interfacial biomolecules. Using these fingerprints, layers composed of structurally related proteins with differing geometries can be discriminated. Thus, we demonstrate a powerful tool for the bioanalytical toolbox.

Singlet exciton diffusion was studied in the efficient organic photovoltaic electron donor material DTS(FBTTh 2 ) 2 . Three complementary time-resolved fluorescence measurements were performed: quenching in planar heterojunctions with an electron acceptor, exciton-exciton annihilation, and fluorescence depolarization. The average exciton diffusivity increases upon annealing from 1.6 × 10 -3 to 3.6 × 10 -3 cm 2 s -1 , resulting in an enhancement of the mean two-dimensional exciton diffusion length (L D = (4Dτ) 1/2 ) from 15 to 27 nm. About 30% of the excitons get trapped very quickly in as-cast films. The high exciton diffusion coefficient of the material leads to it being able to harvest excitons efficiently from large donor domains in bulk heterojunctions.

The refractive index sensitivity of plasmonic fields has been exploited for over 20 years in analytical technologies. While this sensitivity can be used to achieve attomole detection levels, they are in essence binary measurements that sense the presence/absence of a predetermined analyte. Using plasmonic fields, not to sense effective refractive indices but to provide more "granular" information about the structural characteristics of a medium, provides a more information rich output, which affords opportunities to create new powerful and flexible sensing technologies not limited by the need to synthesize chemical recognition elements. Here we report a new plasmonic phenomenon that is sensitive to the biomacromolecular structure without relying on measuring effective refractive indices. Chiral biomaterials mediate the hybridization of electric and magnetic modes of a chiral solid-inverse plasmonic structure, resulting in a measurable change in both reflectivity and chiroptical properties. The phenomenon originates from the electric-dipole-magnetic-dipole response of the biomaterial and is hence sensitive to biomacromolecular secondary structure providing unique fingerprints of α-helical, β-sheet, and disordered motifs. The phenomenon can be observed for subchiral plasmonic fields (i.e., fields with a lower chiral asymmetry than circularly polarized light) hence lifting constraints to engineer structures that produce fields with enhanced chirality, thus providing greater flexibility in nanostructure design. To demonstrate the efficacy of the phenomenon, we have detected and characterized picogram quantities of simple model helical biopolymers and more complex real proteins.

Chromophores containing a donor-π-acceptor (D-π-A) motif have been shown to exhibit many interesting photophysical properties. The lowest electronic transition of a flavin derivative containing this motif, azobenzylflavin (ABFL), has previously been shown to be highly sensitive to solvent environment and hydrogen bonding ligands. To better understand this sensitivity, we have investigated the excited state charge redistribution and dynamics of ABFL in a low-dielectric, non-hydrogen bonding solvent by steady-state Stark and femtosecond optical transient absorption spectroscopies. The Stark measurements reveal the difference dipole moment, Δμ01, between the ground and first excited states to be 22.3 ± 0.9 D. The direction of Δμ01 in the molecular frame was assigned with the aid of TD-DFT and finite field calculations, verifying the hypothesis that electron density moves from the diethylaniline donor to the flavin acceptor in the excited state. The magnitude of the difference dipole moment was used to estimate the hyperpolarizability of ABFL, β0 = 720 × 10(-30) esu. Subsequent excited state decay via charge recombination was shown to take place in a few picoseconds. The data was best fit to a kinetic model composed of a sub-picosecond internal conversion step from S2→S1, followed by a 5 ps decay to the ground state. A competing process involving formation of an additional long-lived state from S1 was also observed. Cyclic voltammetry shows one oxidation and two reduction waves and is completely reversible. This analysis lays the groundwork for developing new flavin dyads with the desired excited electronic state properties for applications such as nonlinear optical devices, molecular electronics applications, or dye-sensitized solar cells.

We have demonstrated controlled assembly between CdSe quantum dots (QDs) and a fullerene (C60) derivative via complementary three-point hydrogen bonding interactions. The recognition-mediated assembly facilitated an interpenetrated network morphology and hence efficient charge transfer from QD to C60.

Flavins feature multiple attributes that explain their widespread occurrence in nature, including photostability, reversible electrochemistry, and especially the tunability of their optical, electronic, and redox properties by supramolecular interactions and modification of their chemical structure. Flavins are important redox cofactors for enzymatic catalysis and are central to a wide variety of processes, including biosynthesis, electron transport, photosynthesis, and DNA repair. The wide range of processes catalyzed by flavins makes them promising leads for synthetic catalysts. Their properties are also relevant to organic electronic and optoelectronic devices, where they have the potential to serve as photoactive electron carriers, a very uncommon property in current photovoltaic systems. In flavoenzymes, the flavin cofactor binds to the active site of the apoenzyme through noncovalent interactions. These interactions regulate cofactor recognition and tune the redox behavior of the flavin cofactor. In this Account, we describe the creation of host-guest systems based on small molecule, polymer, and nanoparticle scaffolds that explore the role of aromatic stacking on the redox properties of the flavin and provide insight into flavoenzyme function. We also describe the creation of synthetic flavin-based interlocked structures featuring aromatic stacking interactions, along with the use of aromatic stacking to direct self-assembly of flavin-based materials. The interplay between redox events and aromatic stacking interactions seen in these synthetic models is important for fundamental understanding of biological systems including the flavoenzymes. The precise control of aromatic interactions and binding of flavins not only underpins their biological activity but gives them the potential to be developed into novel organic optoelectronic materials based on tuned synthetic flavin-receptor assemblies. In a broader context, the redox properties of the flavin provide a very concise tool for looking at the role of electronics in aromatic stacking, an issue of general importance in biological and supramolecular chemistry.

[reaction: see text] A random copolymer containing 1,5-dialkyloxynaphthalene moieties has been synthesized using atom-transfer radical polymerization. We have shown that this polymer has the ability to form complexes with the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)) and that electrochemical reduction of the cyclophane or the addition of a competing guest for the cavity of the cyclophane results in disassembly of the supramolecular polymer.

[reaction: see text] We report the synthesis of flavin-stoppered hydrogen bonded [2]rotaxanes 1 and 2. We also report the electrochemically controllable properties of these systems in solution, and for derivative 2, as an electropolymerized thin film.

[reaction: see text] A new self-complexing donor-acceptor system has been synthesized that has the propensity to undergo intramolecular decomplexation under thermal and electrochemical perturbation and upon addition of a competitive guest for the cyclophane's cavity.

[reaction: see text] A model system has been developed to study the redox behaviors of flavin derivatives appended onto random polystyrene copolymers through "click" chemistry strategies. The results demonstrate that flavin units attached onto polymers exhibit site-isolated redox behaviors, yielding new materials with electrochemically tunable associations (K(a)(ox) = 450 M(-)(1), K(a)(red) = 18,200 M(-)(1)) to complementary diamidopyridine (DAP) functionality.

[structure: see text] A model system has been developed to study the synergy between aromatic stacking and hydrogen bonding in the binding of a flavin derivative. The results show that the identity of both the hydrogen bonding and pi-stacking units strongly determine the overall receptor affinity for flavin in both the oxidized and radical anion forms.