Conjugated Molecules and Polymers in Secondary Batteries: A Perspective

Intrinsically conducting polymers constituting a subclass of macromolecules, as well as a still growing family of large, conjugated molecules, oligomers, and polymers, have attracted research interest for the recent decades. Closely corresponding to the fascination of these materials, combining typical properties of organic polymers and metallic materials, numerous applications have been suggested, explored, and sometimes transferred into products. In electrochemistry, they have been used in various functions beyond the initially proposed and obvious application as active masses in devices for electrochemical energy conversion and storage. This perspective contribution wraps up basic facts that are necessary to understand the behavior and properties of the oligo and polymers and their behavior in electrochemical cells for energy conversion by electrode reactions and associated energy storage. Representative examples are presented and discussed, and an overview of the state of research and development is provided. Particular attention is paid to stability and related aspects of practical importance. Future trends and perspectives are indicated.

Secondary Through-Space Interactions: Achieving Single-Molecule White-Light Emission from Clusteroluminogens with Isolated Phenyl Rings

Clusteroluminogens (CLgens) refer to some non-conjugated molecules that show visible light due to the formation of aggregates and unique electronic properties with through-space interactions (TSI). Although mature and systematic theories of molecular photophysics have been developed to study conventional conjugated chromophores, it is still challenging to endow CLgens with designed photophysical properties by manipulating TSI. Herein, three CLgens with non-conjugated donor-acceptor structures and different halide substituents with secondary TSI are designed and synthesized. These molecules show multiple emissions and even white-light emission in the crystalline state and the intensity ratio of these multiple emission peaks is easily manipulated by changing the halide atom and excitation wavelength. Experimental and theoretical results successfully disclose the electronic nature of these multiple emissions: through-space conjugation for short-wavelength fluorescence, through-space charge transfer based on secondary TSI for long-wavelength fluorescence, and room-temperature phosphorescence. The introduction of secondary TSI to CLgens not only enriches their varieties of photophysical properties but also inspires the establishment of novel aggregate photophysics for clusteroluminescence.

Chiral induction in a novel self-assembled supramolecular system composed of α-cyclodextrin porous liquids, chiral silver nanoparticles and planar conjugated molecules

The newly developed porous liquids known as liquids with permanent microporosity, are of considerable application potential which still has many unknown areas. Herein, a supramolecular system composed of α-cyclodextrin porous...

Fluorescent supramolecular polymers of barbiturate dyes with thiophene-cored twisted π-systems

Because supramolecular polymerization of emissive p-conjugated molecules depends strongly on p–pstacking interaction, the formation of well-defined one-dimensional nanostructures often results in decrease or only small increase of emission efficiency. This is also true...

Three-Dimensional Fully pi-Conjugated Macrocycles: When Truly 3D-Aromatic and when 2D-Aromatic-in-3D?

Recently, several fully pi-conjugated macrocycles with strongly puckered or cage-type structures have been synthesized and found to exhibit aromatic character according to both experiments and computations. Herein, we examine their electronic structures and put them in relation to truly 3D-aromatic molecules (e.g., closo-boranes and certain charged fullerenes) as well as 2D-aromatic polycyclic aromatic hydrocarbons. We use qualitative theory combined with quantum chemical calculations, and find that the macrocycles explored thus far should be described as 2D-aromatic with three-dimensional structures (abbr. 2D-aromatic-in-3D) instead of truly 3D-aromatic. Besides fulfilling the 6n + 2 pi-electron rule, 3D-aromatic molecules with highly symmetric structures (e.g., Td and Oh) have a number of molecular orbital (MO) levels that are (at least) triply degenerate. At lower symmetries, the triple (or higher) orbital degeneracies should be kept in approximate sense. This last criterion is not fulfilled by macrocyclic cage molecules that are 2D-aromatic-in-3D. Their aromaticity results from a fulfillment of Hückel’s 4n + 2 rule for each individual macrocyclic path, yet, their pi-electron counts are coincidentally 6n + 2 numbers for macrocycles with three tethers of equal lengths. We instead link the 3D-macrocyclic molecules explored earlier to naphthalene, motivating their description as 2D-aromatics albeit with 3D structures. It is notable that macrocyclic cages which are 2D-aromatic-in-3D can be aromatic also when the tethers are of different lengths, i.e., when their pi-electron counts differ from 6n + 2. Finally, we identify tetrahedral and cubic pi-conjugated molecules that fulfill the 6n + 2 rule and which exhibit significant electron delocalization. Yet, their properties are similar to those of analogous compounds with electron counts that differ from 6n + 2. Thus, despite that these tetrahedral and cubic molecules show substantial pi-electron delocalization they should not be classified as true 3D-aromatics.

Conditions for electronic hybridization between transition-metal dichalcogenide monolayers and physisorbed carbon-conjugated molecules

Hybridization effects play a crucial role in determining the electronic properties of hybrid inorganic/organic interfaces. To gain insight into these important interactions, we perform a first-principles study based on hybrid density-functional theory including spin-orbit coupling, focusing on eight representative systems formed by two carbon-conjugated molecules-pyrene and perylene-physisorbed on the transition-metal dichalcogenide monolayers (TMDCs) MoS2, MoSe2 WS2, and WSe2. By means of band unfolding techniques, we analyze the band structures of the considered materials, identifying the contributions of the individual constituents as well as the signatures of their hybridization. Based on symmetry and energetic arguments, we derive general conditions for electronic hybridization between conjugated molecules and underlying TMDCs even when the former do not lie planar on the latter, thus providing the key to predict how their mutual arrangement affect their electronic interactions.

Tuning the Optoelectronic Properties of Cross Conjugated Small Molecules Using Benzodithiophene As a Core Unit With Favorable Photovoltaic Parameters

In a recent study, cross conjugated molecules (BDT-C1 to BDT-C6) based on Benzo [1,2-b:4,5-bʹ] (BDT) as core units linked with different acceptor moieties are designed for encouraging photovoltaic applications. The optoelectronic study has been conducted by density functional theory (DFT) at B3LYP 6-31G (d, p) basis set combination by equating them with recently reported cross conjugated reference (BDT-CR) molecule and to study basic parameters such as frontier molecular orbital , density of states, reorganization energy, maximum absorption, dipole moment, transition density matrix (TDM) and open-circuit voltage (VOC). Six new cross conjugated molecules (BDT-C1 to BDT-C6) with modified acceptor moieties are designed to evaluate their photophysical behavior in photovoltaic cells and the optoelectronic analysis of designed molecules indicates that among all cross conjugated molecules, BDT-C3 molecule exhibited the lowest bandgap value (1.83 eV) and broad absorption (747 nm) spectrum in dichloromethane (DCM) due to extended conjugation in molecule than BDT-CR. TDM results reveal the easy dissociation of exciton due to the transfer of electron density in a diagonal direction from donor to acceptor moieties. The lowest value of electron mobility (0.0030 eV) and hole mobility (0.0027 eV) of BDT-C4 indicates its excellent electron and hole transfer behavior. The newly architecture molecule BDT-C5 displayed the highest VOC value of 1.75 eV concerning PC61BM. All above-mentioned outcomes reflects that our newly architecture cross conjugated molecules are suitable applicants for photovoltaic cells and can exhibit wonderful results in the quest of power conversion efficiency (PCE).

Unsymmetrical Hexafluorocyclopentene-Linked Twisted π-Conjugated Molecules as Dual-State Emissive Luminophores

Dual-state emissive (DSE) luminophores, which can luminesce both in solution and in solid states, have recently attracted significant attention because of their broad applications. However, their development is difficult due to the difference in molecular design between solution- and solid-state luminophores. In this study, DSE luminophores based on unsymmetrical hexafluorocyclopentene-linked twisted π-conjugated structures carrying various substituents to tune the electron-density were designed and synthesized in a single-step reaction from heptafluorocyclopentene or perfluoro-1,2-diphenylcyclopentene derivatives. The twisted π-conjugated luminophores exhibited absorption in the UV region at approximately 330 nm, along with several signals in the high-energy region. Upon irradiating the luminophore solution (wavelength 330 nm), light-green to yellow photoluminescence (PL) was observed in the range of 422–471 nm with high PL efficiency. Theoretical calculations revealed that excitation from ground to excited states altered the structural shape of the luminophores from twisted to planar, leading to red-shifted PL and high PL efficiency (ΦPL). The intense blue PL exhibited by the luminophores in the crystalline state was attributed to their twisted molecular structures that suppressed non-radiative deactivation via the effective blocking of π/π stacking interactions.