Invariant Charge Carrier Dynamics Using a Non-Planar Non-Fullerene Acceptor across Multiple Processing Solvents.

Conventional non-fullerene acceptors (NFAs) typically have planar structures that can enable improved electron mobility and produce more efficient organic photovoltaic devices. A relatively simple A-D-A'-D-A type NFA specifically designed to match with poly(3-hexylthiophene-2,5-diyl) (P3HT) for green-absorbing agrivoltaic applications has been examined using a variety of techniques: microsecond transient absorption spectroscopy, atomic force microscopy, and photoluminescence. Relatively invariant charge carrier decay dynamics are observed in the blend films across a variety of processing solvents. Raman spectroscopy in conjunction with computational studies reveals that this NFA is non-planar and that multiple conformations are present in films, while preserving the crystalline nature of P3HT. The non-planarity of the NFA therefore creates a dispersive acceptor environment, irrespective of processing solvent, and this leads to the observed relative invariance in charge carrier decay dynamics and high tolerance to morphological variation. The findings presented in this work highlight the potential of non-planar materials as acceptors in organic photovoltaic devices.

s-Indacene Revisited: Modular Synthesis and Modulation of Structures and Molecular Orbitals of Hexaaryl Derivatives.

Though s-indacene is an intriguing antiaromatic hydrocarbon of 12 π-electrons, it has been underrepresented due to the lack of efficient and versatile methods to prepare stable derivatives. Herein we report a concise and modular synthetic method for hexaaryl-s-indacene derivatives bearing electron-donating/-accepting groups at specific positions to furnish C2h-, D2h-, and C2v-symmetric substitution patterns. We also report the effects of substituents on their molecular structures, frontier molecular orbital (MO) levels, and magnetically induced ring current tropicities. Both theoretical calculations and X-ray structure analyses indicate that the derivatives of the C2h-substitution pattern adopt different C2h structures with significant bond length alternation depending on the electronic property of the substituents. Due to the nonuniform distribution of the frontier MOs, their energy levels are selectively modulated by the electron-donating substituents. This leads to the inversion of the HOMO and HOMO-1 sequences with respect to those of the intrinsic s-indacene as theoretically predicted and experimentally proven by the absorption spectra at visible and near-infrared regions. The NICS values and the 1H NMR chemical shifts of the s-indacene derivatives indicate their weak antiaromaticity. The different tropicities are explained by the modulation of the HOMO and HOMO-1 levels. In addition, for the hexaxylyl derivative, weak fluorescence from the S2 excited state was detected due to the large energy gap between the S1 and S2 states. Notably, an organic field-effect transistor (OFET) fabricated using the hexaxylyl derivative exhibited moderate hole carrier mobility, a result which opens the door for optoelectronic applications of s-indacene derivatives.

Dianion and Dication of Tetracyclopentatetraphenylene as Decoupled Annulene-within-an-Annulene Models.

The dianion and dication of tetramesityl-substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five- and six-membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene-within-an-annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X-ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the 13 C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22-π and 18-π electron outer perimeters, respectively, and 8-π electron structure at the inner ring. Notably, the dianion has an open-shell character, whereas the dication has a closed-shell ground state.

Excited states engineering enables efficient near-infrared lasing in nanographenes.

The spectral overlap between stimulated emission (SE) and absorption from dark states (i.e. charges and triplets) especially in the near-infrared (NIR), represents one of the most effective gain loss channels in organic semiconductors. Recently, bottom-up synthesis of atomically precise graphene nanostructures, or nanographenes (NGs), has opened a new route for the development of environmentally and chemically stable materials with optical gain properties. However, also in this case, the interplay between gain and absorption losses has hindered the attainment of efficient lasing action in the NIR. Here, we demonstrate that the introduction of two fluoranthene imide groups to the NG core leads to a more red-shifted emission than the precursor NG molecule (685 vs. 615 nm) and also with a larger Stokes shift (45 nm vs. 2 nm, 1026 cm-1vs. 53 cm-1, respectively). Photophysical results indicate that, besides the minimisation of ground state absorption losses, such substitution permits to suppress the detrimental excited state absorption in the NIR, which likely arises from a dark state with charge-transfer character and triplets. This has enabled NIR lasing (720 nm) from all-solution processed distributed feedback devices with one order of magnitude lower thresholds than those of previously reported NIR-emitting NGs. This study represents an advance in the field of NGs and, in general, organic semiconductor photonics, towards the development of cheap and stable NIR lasers.

A Small Molecule with Bridged Carbonyl and Tri-fluoro-aceto-phenone Groups Impedes Microtubule Dynamics and Subsequently Triggers Cancer Cell Apoptosis.

We identified a new microtubule targeted small molecule, which showed significant anticancer activity and induced apoptotic death of cancer cells. Precisely the central bridged carbonyl group and trifluoro-acetophenone group of a bis-benzothiazole molecule (BBT) interacts with tubulin close to the curcumin site and perturbs microtubule dynamics as well as causes microtubule depolymerization. We observed a significant enhancement of fluorescence while BBT interacts with the tubulin through bridged carbonyl moiety, a similar phenomenon to colchicine. Further, BBT activates tumor-suppressing bim and p53-puma axes to inhibit cancer survival. It also shows promising results against a tumor spheroid model. BBT is also capable of tumor regression, which shows that this molecule can serve as a potential template for the design of next-generation microtubule targeted anticancer drugs.

Power of an Organic Electron Acceptor in Modulation of Intracellular Mitochondrial Reactive Oxygen Species: Inducing JNK- and Caspase-Dependent Apoptosis of Cancer Cells.

Here, we demonstrate an interesting strategy of modulating mitochondrial reactive oxygen species (ROS) using the organic electron acceptor molecule carbonyl-bridged bithiazole attached with bis-trifluoroacetophenone (BBT). This molecule was found to affect complex I activity. It has the propensity to bind close to the flavin mononucleotide site of complex I of mitochondria where it traps electron released from nicotinamide adenine dinucleotide (NADH) and elevates intracellular ROS, which suggests that the bridged carbonyl in BBT plays a crucial role in the acceptance of electron from NADH. We understand that the potential of the NADH/NAD+ redox couple and low-lying LUMO energy level of BBT are compatible with each other, thus favoring its entrapment of released electrons in complex I. This effect of BBT in ROS generation activates JNK and p38 stress-dependent pathways and resulted in mitochondrial-dependent apoptotic cell death with the reduction in expression of several important cyto-protecting factors (Hsp27 and NFκB), indicating its potential in inhibition of cancer cell relapse. Intriguingly, we found that BBT is not a P-glycoprotein substrate, which further reveals its excellent anticancer potential. This study enlightens us on how the power of electron acceptor ability became an emerging strategy for modulation of intracellular function.

9,10-Dihydro- as-indacenodithiophenes: Isomers with an as-Indacene Core.

Two isomers of 9,10-dihydro- as-indacenodithiophenes (DIDTs) and the corresponding diketones having an as-indacene core were synthesized. Their thermal, photophysical, and electrochemical properties were investigated, revealing that they depend on the direction of the fusion of the thiophene rings. For the DIDTs, the effect of the mode of ring fusion on the physical properties is discussed by comparison with the previously reported derivatives of DIDT isomers with an s-indacene core. The observed difference between the highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of the DIDT isomers is ascribed to the efficiency of π-conjugation, which depends on α- or ß-linkage between the terminal thiophenes with the central benzene ring. In addition, the effect of the peripheral aromatic ring (thiophene or benzene) is elucidated by comparison with indeno[2,1- a]fluorene (DIF) bearing an as-indacene core. The HOMO levels of DIDTs are significantly raised compared to that of structurally related DIF because of electron-donating character of the thiophene rings. For the DIDT diketones, structural effect due to the proximate carbonyl groups is discussed by comparison with the isomers with remote carbonyl groups. In diketones bearing proximate carbonyl groups, the LUMO levels are destabilized owing to antibonding interaction between the carbonyl oxygen atoms, resulting in approach of the LUMO and LUMO+1 energy levels.

Naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole-Based Nonfullerene Acceptors: Effect of Substituents on the Thiophene Unit on Properties and Photovoltaic Characteristics.

The development of new electron-accepting π-conjugated systems for application as nonfullerene acceptors in organic solar cells (OSCs) is urgently needed. Although π-conjugated systems based on naphtho[1,2-c:5,6-c']bis[1,2,5]thiadiazole (NTz) and naphthalimide (Np) as central and terminal units, respectively, represent possible candidates for nonfullerene acceptors, our knowledge of the structure-property-device performance relationship of these compounds remains limited. We report herein on an investigation of the effect of the substituents on the thiophene (T) linker between NTz and Np on the properties and photovoltaic performance. The photophysical and physicochemical measurements showed that the absorption behavior as well as frontier-orbital energy levels can be fine-tuned by the choice of the substituent on the thiophene rings. Bulk-heterojunction-type OSCs based on these acceptors under blending with poly(3-hexylthiophene) as a donor showed various power conversion efficiencies, ranging from 0.26 to 2.14%. The substituents on the thiophene rings also have a significant influence on the blend film properties, which explain the differences in the short-circuit current densities and fill factors in the OSCs. These results indicate the importance of molecular design in preparing nonfullerene acceptors with NTz and Np units in terms of tuning both the molecular properties of the materials and donor-acceptor interface engineering in the blended films.

Dye-sensitized solar cell from polyaniline-ZnS nanotubes and its characterization through impedance spectroscopy.

Polyaniline (PANI)-zinc sulphide (ZnS) nanocomposites (PAZs) are synthesized by polymerizing aniline in the presence of acetic acid with different concentrations of ZnS nanoparticles (NPs). FESEM and TEM images indicate the nanotube morphology of PANI and ZnS NPs remain adhered to the nanotube surface, but at higher ZnS concentration the nanotube morphology is lost. UV-vis spectra indicate PANI is in the doped state and the doping increases with an increase in ZnS concentration. Fluorescence intensity passes through a minimum with ZnS content and the dc-conductivity of the composites gradually increases with an increase in ZnS NP concentration. The I-V plot of PAZ composites indicates that the photocurrent is higher than that of the dark current at each voltage, and the device exhibits reversible turning "on" and "off" by switching the white light illumination "on" and "off". Dye-sensitized solar cells fabricated with PAZ composites display a reasonably higher power conversion efficiency (η = 3.38%) than pure ZnS NPs. An attempt is made to shed light on the operating mechanism of the DSSC from the impedance data using a Cole-Cole plot by drawing an equivalent circuit illustrating the different electronic and ionic transport processes within the cell.

Poly[3-(2-hydroxyethyl)-2,5-thienylene] grafted reduced graphene oxide: an efficient alternate material of TiO2 in dye sensitized solar cells.

Replacement of the TiO2 layer in a traditional dye sensitized solar cell (DSC) by poly[3-(2-hydroxyethyl)-2,5-thienylene] grafted reduced graphene oxide (PHET-g-rGO) yields an overall power conversion efficiency of 3.06% with the N-719 dye, where the rGO part increases the charge mobility by reducing the backward recombination reaction in the DSC.

Tuning of the morphology of a riboflavin-melamine equimolar supramolecular assembly by in situ silver nanoparticle formation.

Tuning the supramolecular morphology of an equimolar complex of riboflavin and melamine by the in situ formation of different size silver nanoparticles, affecting the photoluminescence property.