Ultrafast High-Energy Micro-Supercapacitors Based On Open-Shell Polymer-Graphene Composites

Micro-supercapacitors are poised to serve as on-chip power sources for electronics. However, the challenge to simultaneously increase their power, energy, and lifetime demands new material combinations beyond current carbon-based systems. Here, we demonstrate that electro-deposition of an open-shell conjugated polymer with reduced graphene oxide achieves electrodes with capacitance up to 186 mF cm−2 (372 F cm−3). The extended delocalization within the open-shell polymer stabilizes redox states and facilitates a 3 V wide potential window, while the hierarchical electrode structure promotes ultrafast kinetics. The micro-supercapacitor shows a high power density of 227 mW cm−2 with an energy density of 10.5 μWh cm−2 and stability of 84% capacitance retention after 11,000 cycles. These attributes allow operation at 120 Hz for fast charging and alternating current (AC) line filtering applications, which may be suitable to replace bulky electrolytic capacitors or serve as high-endurance energy storage for wireless electronics

Topology and Ground State Control In Open-Shell Donor-Acceptor Conjugated Polymers

Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character represent an emerging class of materials whose rich behavior emanates from their collective electronic properties and diminished electron pairing. However, the structural and electronic heterogeneities that define these materials complicate bandgap control at low energies and connections linking topology, exchange interactions, and (opto)electronic functionality remain nascent. To address these challenges, we demonstrate structurally rigid and strongly π-conjugated copolymers comprised of a solubilizing thiadiazoloquinoxaline acceptor and cyclopenta[2,1-b:3,4-b′]dithiophene or dithieno[3,2-b:2′,3′-d]thiophene donors. Atom-specific substitution modulates local aromatic character within the donor resulting in dramatic differences in structural, physicochemical, electronic, and magnetic properties of the polymers. These long-range π-mediated interactions facilitate control between low-spin aromatic and high-spin quinoidal forms. This work provides a strategy to understand the evolution of the electronic structure within DA CPs, control the ground state spin multiplicity, tune spin-spin interactions, and articulate the emergence of their novel properties

How End-Capped Acceptors Regulate the Photovoltaic Performance of the Organic Solar Cells: A Detailed Density Functional Exploration of Their Impact on the A–D−π–D–A Type Small Molecular Electron Donors

Recent investigations on organic solar cells have demonstrated the superior photovoltaic performance of A−π–D−π–A type small molecular electron donors (SMEDs) compared to that of the D–A(π)–A and D–A(π)–D molecular frameworks because of their intense intramolecular charge transfer transitions, narrow band gap, and broad optical profiles at the near-infrared region. These characteristic features mainly originated from their molecular functionalization of the core and end-capped acceptor building blocks, which generate quite a greater impact through the wavefunction overlap of the intra-/intermolecular interactions. Nonetheless, SMEDs with various reported end-capped acceptors, 1,3-indanedione (IND), N-alkyl rhodanine (NAR), and dicyanovinylene (DCV), exhibited excellent photovoltaic performance, the reason behind this phenomenon remains unexplained. To gain better insights in this regard, we have designed a series of SMEDs named DFR, DFM, and DFI by embedding these exceptionally performing NAR, DCV, and IND end-capping units, respectively, into a newly designed A–D−π–D–A molecular framework. A detailed investigation was carried out to understand the influence of end-capped acceptors on the photovoltaic parameters at the molecular level using density functional theory (DFT) and time-dependent DFT methods. Exploration of this study reveals that the NAR unit of the A–D−π–D–A framework (DFR) enabled a bathochromic shift compared to that of the DCV counterpart (DFI), a reverse pattern of absorption to that of the widely reported A−π–D−π–A system. A series of charge transfer parameters related to excited state properties including charge density difference, amount of charge transferred (qCT), charge transfer distance (dCT), dipole variation, H-index, t-index, and hole–electron overlap (S±) and other components such as ionization potential, electron affinity, delocalization, and reorganization energies were computed. In addition, photovoltaic parameters such as exciton binding energy and open-circuit voltage have been systematically evaluated with respect to the fullerene and Y6 electron acceptors. The antiaromatic characteristics of the cyclic NAR and IND acceptors were well-demonstrated using the nucleus-independent chemical shift, 2D isochemical shielding surface, and anisotropy of the induced current density analyses. This study highlights that the performance of each acceptor is distinctively different because it not only can be determined from its electron-withdrawing strength but also depends on its potential to allow the charge density population. The greater heterofunctionalities of NAR and IND acceptors could help increase the Jsc due to its strong accommodating potential of electron density population at the peripherals, but the minimized contribution from the sp-hybridized C≡N unit of the DCV acceptor failed in this regard. The computed results followed an excellent agreement with the experimental observations. The results obtained from this study would be helpful for the researchers to gain a better understanding of the chemistry behind the relationship between the structure of the end-capped acceptors and photovoltaic activity and suggesting the beneficial features of including more heterofunctionalities into large-sized terminal acceptors: (1) band gap narrowing through lowest unoccupied molecular orbital stabilization; (2) efficient ICT transitions; and (3) greater accommodating potential of charge density population at the peripherals, which could help the facilitation of charge transport at the D−A interface

Influence of π-spacers and acceptors in Far-red/NIR AIEE active coumarin based α-cyanostilbenes: a combined experimental and DFT study

by Mahalingavelar Paramasivam and Sriram Kanva

Rational tuning of AIEE active coumarin based α-Cyanostilbenes towards Far-Red/NIR region using different π-Spacer and acceptor units

A series of cyanostilbene based D−π–A derivatives, comprising 6-(diethylamino)coumarin as a donor and benzene and benzothiazole as acceptors bridged by different π-spacers (benzene, thiophene), have been synthesized and characterized. The influence of π-spacer and acceptor units on the photophysical, electrochemical, and thermal properties of the dyes was investigated in detail. The incorporation of coumarin donor results in a significant increase of the fluorescence quantum yield. In the solution phase, the absorption and emission of the dye TB show a bathochromic shift (TB > BBT) indicating dominant dynamic intramolecular rotations (IMR) behavior of cyano group over the acceptor functionality. On the other hand, the emission is reversed (BBT > TB) in the case of aggregates. The synergistic combination of intramolecular planarization and torsional alleviation around cyanostilbenes induced by strong electron withdrawing benzothiazole unit in BBT enabled pronounced bathochromic shift upon aggregation. Upon varying the spacer/acceptor substitution, the emission wavelength of the aggregates shifts from visible to far red/NIR region with concomitant large Stokes shifts of 158–213 nm. The fluorescence intensity of the aggregates gradually decreases with increased planarity of the backbone. Various experimental techniques were employed to evaluate the structure–emission phenomena relationship. The aggregation induced enhanced emission (AIEE) behavior of the dyes was substantiated from fluorescence lifetime decay studies and scanning electron microscopy (SEM) analysis. Density functional theory (DFT) computed band gap follows a consistent trend with the values estimated from electrochemical-optical studies. All the dyes possess excellent thermal stability. Our study demonstrated far-red/NIR AIEE cyanostilbene derivatives exhibiting large Stokes shift having excellent thermal properties and fluorescence quantum yields could act as potential candidates for optoelectronic or imaging applications.by Mahalingavelar Paramasivam and Sriram Kanva

Water soluble AIE luminogen: a fluorescent probe for protein binding

by Mahalingavelar Paramasivam, Anuji K. Vasu and Sriram Kanvah

Photoisomerization of trans ortho-, meta-, para- nitro diarylbutadienes: a case of regioselectivity

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/php.12504by Harsha Agnihotri, Mahalingavelar Paramasivam, Veerabhadraiah Palakollu and Sriram Kanva

Emission and color tuning of cyanostilbenes and white light emission

White-light-emitting diodes are energy efficiency replacement of conventional lighting sources. Herein, we report the luminescent behavior of three simple cyanostilbenes with triphenylamine-donating groups bearing different electron-withdrawing groups (phenyl, pyridyl, and p-nitrophenyl) in a common donor (D)−π–acceptor (A) α-cyanostilbene construct along with their thermal and electrochemical properties. The density functional theory (DFT) studies reveal that aggregation-induced emission characteristic feature of the D−π–A dyes is inversely proportional to the intramolecular charge transfer (ICT) effect, that is, phenyl-and pyridyl-substituted compounds show characteristic aggregation-induced emission in water, whereas the ICT effect is dominant for the nitro derivative. The extent of ICT and the solvatochromic emission shifts, from blue to red, depend on the strength of the electron-withdrawing group. White luminescence and tunable emission colors are obtained by careful admixtures of these cyanostilbenes bearing triphenylamines. The results rationalized through DFT and time-dependent DFT calculations follow a consistent trend with the energy levels measured from the electrochemical and optical studies. Thermogravimetric analysis and differential scanning calorimetry studies showed excellent thermal stability of the compounds. The scanning electron microscopy and dynamic light scattering measurements were performed to reveal the formation of aggregates. This strategy involving synthetically simple and structurally similar molecules with different emission properties has potential applications in the fabrication of multicolor and white-light-emitting materials.by Beena Kumari, Mahalingavelar Paramasivam, Arnab Dutta and Sriram Kanva

Amino substituted 4-pyridylbutadienes: synthesis and fluorescence investigations

Synthesis and spectroscopic investigations of a series of donor-π-acceptor systems containing pyridine as the electron withdrawing group and an amino derivative (dimethylamino, diphenylamino, carbazole and julolidine) as electron donating group, separated by a π-spacer are described. The effect of varying donors on absorption and emission properties was studied in different solvents. All the molecules investigated exhibit pronounced positive polarity dependent solvatochromic shifts of up to ∼141 nm. Strong fluorescence quantum yields are also observed for dienes containing carbazole and diphenylamine donors. This behavior suggests the presence of highly polar emitting states as a result of π -π* intramolecular charge-transfer (ICT). The observations were corroborated by a linear relation of the fluorescence maximum (νmax) versus the solvent polarity function (Δf) from the Lippert–Mataga correlation. The emission lifetime shows a decay profile consistent with the formation of one species (1 and 3) and two species (2 and 4) in the excited state.by Harsha Agnihotri, et.a

A Competitive Effect of Acceptor Substitutions On the Opto-Electronic Features of Triphenylamine Cored Di α-Cyanostilbene Derivatives

Three novel triphenylamine cored di-branched α-cyanostilbenes with different electron-acceptors [H (neutral), CF3, and NO2] were synthesized. All the compounds exhibited a distinct positive solvatochromism dependent on the polarity and nature of the acceptor unit. Emission in binary solvent mixture reveals that CF3substituted chromophores promote the AIE effect with moderate emission wavelength shift. In contrast, NO2substitution drives the emission to a longer wavelength due to pronounced ICT but with quenched emission. Introducing CF3and NO2into a single molecule has a competing effect,i.e., balancing the pull-pull interactions enabled the enhancement of ICT characteristics with a moderate ACQ to AIE effect. These studies reveal that electron-accepting functionalities create a considerable impact on an otherwise identical template\u27s optoelectronic characteristics. DFT and TDDFT analysis correlate the absorption and wavelength shift with acceptor functionality, and DOS-PDOS analysis helps predicting their photophysical characteristics upon photoexcitation. PES scan studies demonstrated that arms with strong acceptor units increased the energy barrier of dynamic intramolecular rotation of the α-cyano unit