Push-pull Systems Research Articles

Exploring the role of π-Spacers in six novel Push-Pull photovoltaic systems based on N-Methylarylamine: A theoretical DFT Investigation

This study examines the impact of spacers on the performance of six push–pull type molecules (D-π-A) in solar cells. MPTA-1 (without a spacer) is compared to MPTA-2 to MPTA-6, which incorporate thiophene, benzothiazole (BTZ), furane, selenophene, and pyridine spacers. N-phenyl-N-(thiazol-2-yl)aniline (MPTA) is the donor, and dicyanovinyl (DCV) is the acceptor in all molecules. Quantum chemical calculations using Density Functional Theory (DFT) confirm these compounds as suitable electron donors with acceptors like PCBM in bulk-heterojunction solar cells. Key findings: i) molecules absorb in the visible range (446.54 nm to 671.23 nm); ii) energy gaps range from 1.34 eV to 2.21 eV, making them suitable for photovoltaics; iii) MPTA-4 shows the highest power conversion efficiency (PCE) at 14.363 % due to its higher open circuit voltage (Voc) of 1.848 V. The furane spacer significantly enhances photovoltaic properties, making MPTA-4 the most efficient.

The genetics of plant-plant interactions and their cascading effects on agroecosystem - from model plants to application.

Plants are typically surrounded by neighboring individuals in agricultural fields or natural environments. In such circumstances, plant-plant interactions (PPI) are ubiquitous and represent not only important evolutionary forces but also have consequences on (agro-)ecosystem functioning, such as increased productivity and resistance. However, many mechanisms underlying these PPIs remain poorly understood. Recently, new genomic technologies and tools, such as genome-wide association studies, have facilitated genetic approaches to study PPIs, particularly among conspecific individuals. Here, we highlight emerging issues and advances in the field by focusing on three different aspects. First, we overview the current status of genetic mapping studies on PPIs and pinpoint that these studies open a new opportunity that is relevant to agriculture and breeding. Second, we introduce two proof-of-concept studies in Arabidopsis thaliana, in which genetic differences among plants improved the functioning of genotype mixtures. Both studies were able to predict effective mixtures with different experimental designs applied to different outcomes (productivity increase vs. herbivory mitigation). Third, we discuss implications from these case studies about how PPIs have cascading effects that propagate to higher levels of biological organization, such as populations or communities. At the population level, plant yield or resistance can be optimized through breeding that achieves reduced competition or push-pull protection systems, respectively. At the community level, these population-level changes may have further beneficial effects on plant-associated organisms. Overall, we suggest that the increasing availability of genomic resources will improve our understanding of PPIs and thereby contribute to the management of crops or semi-natural ecosystems.

Tuning the Thermal Stability of Tetra-o-chloroazobenzene Derivatives by Transforming Push-Pull to Push-Push Systems.

Molecular photoswitches provide interesting tools to reversibly control various biological functions with light. Thanks to its small size and easy introduction into the biomolecules, azobenzene derivatives have been widely employed in the field of photopharmacology. All visible-light switchable azobenzenes with controllable thermostability are highly demanded. Based on the reported tetra-o-chloroazobenzenes, we synthesized push-pull systems, by introducing dialkyl amine and nitro groups as strong electron-donating and electron-withdrawing groups on the para-positions, and then transformed to push-push systems by a simple reduction step. The developed push-pull and push-push tetra-o-chloroazobenzene derivatives displayed excellent photoswitching properties, as previously reported. The half-life of the Z-isomers can be tuned from milliseconds for the push-pull system to several hours for the push-push system. The n-π* and π-π* transitions have better resolution in the push-push molecules, and excitation at different wavelengths can tune the E/Z ratio at the photostationary state. For one push-pull molecule, structure and absorption spectra obtained from theoretical calculations are compared with experimental data, along with data on the push-push counterpart.

Bicyclic-Ammonium-Incorporated Ylidic Nitrogen Groups for Strong π-Electron Donation in Push-Pull Benzene π-Conjugated Systems.

Ylidic nitrogen-based π-electron-donating groups, (quinuclidinio)amidyl (QA) and (1-azanorbornanio)amidyl (ANA) groups, were developed to shift the absorption of push-pull benzenes toward longer wavelengths. Changing the pyrrolidinyl group to the QA or ANA group achieved a bathochromic shift of 45-100 nm in the maximum absorption wavelength, depending on the push-pull π-conjugated system investigated (p-nitrobenzene, 1,8-naphthalimide, and an azo dye).

Effect of dipolar state on J-type aggregation of acceptor group modified pyrene-based push-pull systems

The present work demonstrates the ground and excited state aggregation behavior of two pyrene-based push–pull systems (Pyr-MC and Pyr-PyA) both in solid and solution state. The UV–Vis spectra of these molecules show a unique broaden spectral pattern at lower energy region (400–600 nm) in both H2O and solid state. Further, along with the local (intense) emission band, a new (less intense) band is appeared at higher wavelength region (∼550 nm) in water, which is due to the formation of aggregates. Interestingly, it is the lowest energy emission out of all previously reported emission by pyrene derivatives. The experimental results suggest the formation of J-type aggregation in solid and solution. The average lifetime of these molecules is also measured in different solvents. Intriguingly, the ground/excited state J-type aggregation in solid and solution are similar in nature in spite of different mode of intermolecular interactions, and are supported by experimental results. The dipolar state plays an important role on the J-type aggregation process. The QTAIM (quantum theory of atom in molecule) theoretical framework is applied to analyze and understand the properties of molecules in terms of the distribution of electrons and the topological features of the electron density within a molecule. Importantly, bond paths provide information about the nature of chemical bonds, including their strength and directionality.

Structure, tree diversity, and aboveground carbon stocks of smallholder farms with push-pull technology in western Kenya

Push-pull technology is a companion cropping system whose success in soil fertility improvement and management of agricultural pests has been established in cereal-based systems. Push-pull has also been proposed as a template for the sustainable intensification of agriculture in Africa. However, the application of the technology has remained on a field scale and is restricted to cereal-based systems. Trees in agricultural landscapes are considered a strategy for climate change mitigation by storing carbon in soils and woody biomass. However, their potential has not been quantified in push-pull systems. This study characterized 45 smallholder farms in western Kenya to establish the land use categories within which push-pull is integrated, the diversity and structure of perennials on the farms, and the aboveground carbon stored within those farms. The area of each land use category varied depending on the size of the land use category on each farm. The amount of carbon stored in aboveground biomass was estimated using an existing allometric equation. This study found that trees are integrated on farms with push-pull in homesteads (45), cropland (38), woodlots (26), boundaries (4), and grazing land (2) farms. A total of 9159 trees from 97 different species were recorded over 34 ha. Farms in Vihiga and Kisumu had more trees (38 % and 37 % of all trees recorded) than those in Siaya (25 %). There were more trees in woodlots (total=4518) and homesteads (total=3327), and the least in grazing land (total=18). Overall, the highest species richness, Shannon, and Simpson diversity were observed in the homestead (86 species, H’=2.52 and D = 0.86). Farms in Kisumu, Vihiga, and Siaya stocked an average of 12.1, 9.4, and 7.3 Mg C ha−1 in aboveground biomass respectively. Variations were observed in land use categories, where woodlots had the greatest amount of carbon (55.5 Mg C ha−1) while grazing land had the least (2.4 Mg C ha−1). Eucalyptus spp., Grevillea robusta, and Markhamia lutea were the most dominant trees in abundance at 50 %, 16 %, and 11 % respectively. Conservation of trees on farms should be encouraged, as they protect biodiversity and store carbon thus contributing to climate change mitigation. This study's findings contribute to knowledge valuable to farmers and policymakers in making decisions on tree species and land use categories that have a high potential to sequester carbon in agroforestry systems.

Resolution of 9,10-Diketo[7]helicene and Its Use in One-Step Preparation of Helicene-Based D-A-D Push-Pull Systems.

Racemic 9,10-diketo[7]helicene was successfully separated into enantiomers using a reversible and stereoselective reaction with 2,2'-diamino-1,1'-binaphthalene with moderate yields but with remarkable purity (>99% de). The enantiomerically pure diketone was used as a convenient starting material for the preparation of helicene-based push-pull molecules, which incorporated aza-aryl acceptors and diarylaminophenylene donor groups in a single step. A series of six push-pull systems, along with three reference molecules without donors, were prepared and studied using UV/vis and fluorescence measurements, circular dichroism, and DFT calculations.

Synthesis of Styrylbenzazole Photoswitches and Evaluation of their Photochemical Properties.

Styrylbenzazoles form a promising yet under-represented class of photoswitches that can perform a light-driven E-Z isomerization of the central alkene double bond without undergoing irreversible photocyclization, typical of the parent stilbene. In this work, we report the synthesis and photochemical study of 23 styrylbenzazole photoswitches. Their thermal stabilities, quantum yields, maximum absorption wavelengths and photostationary state (PSS) distributions can be tuned by changing the benzazole heterocycle and the substitution pattern on the aryl ring. In particular, we found that push-pull systems show large redshifts of the maximum absorption wavelengths and the highest quantum yields, whereas ortho-substituted styrylbenzazole photoswitches exhibit the most favorable PSS ratios. Taking advantage of both design principles, we produced 2,6-dimethyl-4-(dimethylamino)-styrylbenzothiazole, a thermally stable and efficient P-type photoswitch which displays negative photochromism upon irradiation with visible light up to 470 nm to obtain a near-quantitative isomerization with a very high quantum yield of 59 %. Furthermore, 4-hydroxystyrylbenzoxazole was demonstrated to be a pH-sensitive switch which exhibits a 100 nm redshift upon deprotonation. Ortho-methylation of its benzothiazole analogue improved the obtained PSS ratio in its deprotonated state from E : Z=53 : 47 to E : Z=18 : 82. We anticipate that this relatively unexplored class of photoswitches will form a valuable expansion of the current family of photoswitches.

Near-IR Capturing N-Methylbenzene Sulfonamide-Phenothiazine Incorporating Strong Electron Acceptor Push-Pull Systems: Photochemical Ultrafast Carrier Dynamics.

Unraveling the intriguing aspects of the intramolecular charge transfer (ICT) phenomenon of multi-modular donor-acceptor-based push-pull systems are of paramount importance considering their promising applications, particularly in solar energy harvesting and light-emitting devices. Herein, a series of symmetrical and unsymmetrical donor-acceptor chromophores 1-6, are designed and synthesized by the Corey-Fuchs reaction via Evano's condition followed by [2+2] cycloaddition retroelectrocyclic ring-opening reaction with strong electron acceptors TCNE and TCNQ in good yields (~60-85 %). The photophysical, electrochemical, and computational studies are investigated to explore the effect of incorporation of strong electron acceptors 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) and dicyanoquinodimethane (DCNQ) with phenothiazine (PTZ) donor. An additional low-lying broad absorption band extended towards the near-infrared (NIR) region suggests charge polarization after the introduction of the electron acceptors in both symmetrical and asymmetrical systems, leading to such strong ICT bands. The electrochemical properties reveal that reduction potentials of 3 and 6 are lower than those of 2 and 5, suggesting DCNQ imparts more on the electronic properties and hence largely contributes to the stabilization of LUMO energy levels than TCBD, in line with theoretical observations. Relative positions of the frontier orbitals on geometry-optimized structures further support accessing donor-acceptor sites responsible for the ICT transitions. Eventually, ultrafast carrier dynamics of the photoinduced species are investigated by femtosecond transient absorption studies to identify their spectral characteristics and target analysis further provides information about different excited states photophysical events including ICT and their associated time profiles. The key findings obtained here related to excited state dynamical processes of these newly synthesized systems are believed to be significant in advancing their prospect of utilization in solar energy conversion and related photonic applications.

Integrating vegetables in push-pull technology systems: gendered preferences of smallholder farmers in western Kenya

Transformative rural smallholder agriculture addressing biophysical constraints requires farmer-led innovations for increased technology adoption. Following the need to further intensify the cereal push-pull technology (PPT) for pest and weed control through integration with vegetables, we conducted surveys to determine suitable vegetables across three different counties in Kenya namely Homabay, Siaya, and Trans-Nzoia. Farming in these areas is predominantly maize based and introducing vegetables to the system will improve household food and nutritional security, together with income. A systematic random sampling method was used to sample a total of 124 smallholder farmers who were interviewed during field days where farmer awareness of technology was mobilised. Descriptive results showed kale (47%) and black nightshade (30%) were the most preferred high-value vegetables for integration into push-pull plots in these regions. This was followed by cowpea (15%), onion (6%) and tomato (2%) underlying the wide range of farmer preferences and priorities. There were also gender differences in vegetable preferences with men preferring capital intensive and high value vegetables, while women preferred traditional vegetables. Results from multinomial logit model revealed that age of the farmer, education level, gender, and farming experience were determinants of smallholder farmers’ vegetable preferences for integration into the PPT plots. The contribution of these determinants to farmer preferences varied across different vegetables where the contribution of the market value of the vegetable in selection diminished with while the effect of farmers’ age. Overall, male farmers preferred capital-intensive and market-oriented vegetables in compared to their female counterparts. We conclude that gender and geographic location play a pivotal role in farmers` crop selection for integration in the PPT. Targeted awareness creation pathways accounting for these factors will be critical for wider adoption of the PPT. Key words: Food security, Multinomial Logistic Regression Model, Participatory rural appraisal, Sustainable agricultural intensification, Technology adoption

Governing the emissive properties of 4-aminobiphenyl-2-pyrimidine push-pull systems via the restricted torsion of N,N-disubstituted amino groups.

Donor-acceptor-substituted biphenyl derivatives are particularly interesting model compounds, which exhibit intramolecular charge transfer because of the extent of charge transfer between both substituents. The connection of a 4-[1,1'-biphenyl]-4-yl-2-pyrimidinyl) moiety to differently disubstituted amino groups at the biphenyl terminal can offer push-pull compounds with distinctive photophysical properties. Herein, we report a comprehensive study of the influence of the torsion angle of the disubstituted amino group on the emissive properties of two pull-push systems: 4-[4-(4-N,N-dimethylaminophenyl)phenyl]-2,6-diphenylpyrimidine (D1) and 4-[4-(4-N,N-diphenylaminophenyl)phenyl]-2,6-diphenylpyrimidine (D2). The torsion angle of the disubstituted amino group, either N,N-dimethyl-amine or N,N-diphenyl-amine, at the biphenyl end governs their emissive properties. A drastic fluorescence quenching occurs in D1 as the solvent polarity increases, whereas D2 maintains its emission independently of the solvent polarity. Theoretical calculations on D1 support the presence of a twisted geometry for the lowest energy, charge-transfer excited state (S1,90), which corresponds to the minimum energy structure in polar solvents and presents a small energy barrier to move from the excited to the ground state, thereby favoring the non-radiative pathway and reducing the fluorescence efficiency. In contrast, this twisted structure is absent in D2 due to the steric hindrance of the phenyl groups attached to the amine group, making the non-radiative decay less favorable. Our findings provide insights into the crucial role of the substituent in the donor moiety of donor-acceptor systems on both the singlet excited state and the intramolecular charge-transfer process.

Excited-State Charge Transfer in Push-Pull Platinum(II) π-Extended Porphyrins Fused with Pentacenequinone.

Platinum(II) π-extended porphyrins fused with pentacenequinone and dihydropentacene have been successfully synthesized. These porphyrins were investigated using various techniques including absorption, steady-state, and time-resolved phosphorescence spectroscopy and differential pulse voltammetry. UV-vis absorption spectra of pentacenequinone-fused porphyrins (SW-Pt1 and SW-Pt2) showed unusually broad and nontypical absorption patterns. Phosphorescence spectra of SW-Pt1, SW-Pt2, and SW-Pt3 displayed similar emissions in the 704-706 nm region indicating electronic transitions of similar origin; however, the triplet lifetimes were found to be quenched in the case of both SW-Pt1 and SW-Pt2, suggesting the occurrence of excited-state events. Facile reductions were obtained for both the pentacene-quinone-fused monomer (SW-Pt2) and dimer (SW-Pt1) and were identified to be located at the pentacenequinone components. The observed orbital segregations for SW-Pt2 and SW-Pt1 from DFT calculations supported the possibility of charge transfer in these push-pull systems. Interestingly, the established energy level diagram revealed that the charge transfer from the triplet excited Pt porphyrin is thermodynamically an uphill process. Systematic studies involving both femtosecond and nanosecond transient absorption techniques revealed that the singlet excited Pt porphyrins undergo an intermediate charge transfer state prior to populating the triplet state, providing a plausible explanation for phosphorescence quenching. The lifetime of the intermediate charge transfer states was found to be 25.9 and 5.68 ps, respectively, for SW-Pt1 and SW-Pt2.

Farmers’ perceived pathways for further intensification of push-pull systems in Western Kenya

Push-pull technology provides farmers in East Africa with an eco-friendly strategy that increases crop yield and household income in smallholder cereal systems by controlling pests and improving soil health. Though promising for a sustainably intensified production, push-pull has been used at limited scale, primarily in maize-and sorghum-based production systems. Expanding the scope, applicability and acceptance of the practice in smallholder farming systems, will leverage the full potential of push-pull as a widely applicable sustainable farming practice. Using key informant interviews and focus group discussions, we explored farmers’ needs and perceived pathways for integrating push-pull and other sustainable intensification practices in synergy with existing cropping systems in Kisumu, Vihiga and Siaya Counties in Western Kenya. We found that farmers in the region typically grow and intercrop a variety of crops, with maize being the most common crop. Farmers commonly practice crop-livestock farming, intercropping, crop rotation, manure and fertilizer use, and use improved varieties to increase maize production. Across the counties, integration of food legumes, agroforestry and crop-livestock farming, were identified as fundamental pathways for stretching the benefits of push-pull. Limitations to farmers’ aspirations and key enablers for facilitating spontaneous adoption of identified sustainable intensification practices for push-pull farming systems are discussed.

Far-Red Excitation Induced Electron Transfer in Bis Donor-AzaBODIPY Push-Pull Systems; Role of Nitrogenous Donors in Promoting Charge Separation.

A far-red absorbing sensitizer, BF2-chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push-pull systemslinked with a series of nitrogenous electron donors, viz., N,N-dimethylaniline, triphenylamine, and phenothiazine via an acetylene linker. The structural integrity of the newly synthesized triads was established by spectroscopic, electrochemical, spectroelectrochemical, and DFT methods. Differential pulse voltammetry studies revealed different redox states and helped in the estimation of the energies of the charge-separated states. Further, spectroelectrochemical studies performed revealed diagnostic peaks of azaBODIPY•- in the visible and near-IR regions. Free-energy calculations revealed the charge separation from one of the covalently linked donors to the 1azaBODIPY* to yield Donor•+-azaBODIPY•- to be energetically favorable in a polar solvent, benzonitrile. The femtosecond pump-probe studies revealed the occurrence of excited charge transfer (CT) in nonpolar toluene while a complete charge separation (CS) for all three triads in polar benzonitrile. The CT/CS products populated the low-lying 3azaBODIPY* prior to returning to the ground state. Global target (GloTarAn) analysis of the transient data revealed the lifetime of the final charge-separated states (CSS) to be 195 ps for NND-derived, 50 ps for TPA-derived, and 85 ps for PTZ-derived triads in benzonitrile.

The realization of parallel airflow after flow rectification by the perforated plate under complex inflows

The parallel push-pull ventilation system uses uniform, low turbulence, and wide parallel airflow to achieve low diffusion transport of pollutants and reduce the system's energy consumption. Complex inflows caused by local connectors (fans, elbows, and reducers) in front of the air supply device seriously affect the air supply distribution. Currently, most existing studies focus on the performance of parallel push-pull ventilation systems, while lacking theoretical support and parameter guidance to rectify these complex inflows into parallel airflow. This study investigates parallel airflow after rectifying various complex inflows using perforated plates. Within the study context, three typical complex inflows models (fan, elbow, and reducer inflows) are established using dominant numerical and supporting experimental methods. In addition, the rectification effects of inflow velocity, porosity, and hole size of the perforated plate on various complex inflows are compared. The results show that the perforated plate's porosity and hole size should be reasonably matched under different complex inflows to achieve a uniform and low turbulence parallel flow. The perforated plate should have a porosity between 40% and 55% and a dimensionless hole size between 0.014 and 0.031 for elbow and reducer inflows. Swirling flow causes a reduction in the perforated plate's rectification capacity for fan inflow, requiring lower porosity and hole size, while also meaning that the resistance increases significantly. Overall, the study results are anticipated to aid in achieving supply airflow with parallel airflow.

Push-pull technology enhances resilience to climate change and prevents land degradation: Perceptions of adopters in western Kenya

Climate change and land degradation adversely affect food security in sub-Saharan Africa (SSA). Smallholder farmers are the most affected. Therefore, it is imperative to identify technologies that boost resilience to climate change, and restore lands. Push-pull technology is among proposed solutions. This technology controls stem borers, fall armyworm, striga, mycotoxins; improves availability of nitrogen and phosphorus, and stores increased carbon in biomass and soils. Though much has been published about push-pull technology, there is a lean in publications about how this technology can help smallholder farmers to cope with climate change and variability. Here, we present perceptions of adopters of push-pull technology in western Kenya with regard to climate change and land degradation, and discuss reasons it should be adopted widely. We compared push-pull and other maize-based cropping systems in western Kenya, through interviews. Push-pull technology produces 0.3–1.1 ​t more maize ha−1 compared to maize-bean intercrop, and maize monocrop when the season is drier than normal. Additionally, push-pull provides 3.6–9.8 ​t more fodder during drought-stricken seasons. Push-pull technology covers 70% of the soil surface compared to 20% cover found in maize-bean intercrop and maize monocrop. In push-pull farms, 150–280 ​kg nitrogen, 13–24 ​kg phosphorus and 370–470 ​kg potassium can be recycled through biomass and this is five times greater than the potential for maize-bean intercrop and maize monocrop. There is need for wide adoption of push-pull technology to increase resilience of farmers to climate change and restore degraded lands.

Symmetrically Functionalized Copper and Silver Corrole-Bis-Tetracyanobutadiene Push-Pull Conjugates: Efficient Population of Triplet States via Charge Transfer.

Copper and silver tritolylcorroles (TTC) are symmetrically functionalized to carry two tetracyanobutadiene (TCBD) entities via [2+2] cycloaddition-retroeletrocyclization reaction involving ethynyl functionalized corroles with an electron acceptor, tetracyanoethylene (TCNE) in excellent yields, as the first examples of corrole-TCBD push-pull systems. The strong push-pull effect resulted in charge polarization in the ground state resulting in a considerable hypsochromic shift of the spectrum extending it into the near-IR region. Electrochemical studies coupled with computational studies revealed considerable interactions between the two TCBD entities via the corrole π-system and the degree of such interactions was found to depend on the metal ion present in the corrole cavity. Energy considerations suggested charge transfer (CT) from the S2 or vibrationally hot S1 state but not the relaxed S1 state in the case of CuTTC(TCBD)2 while CT to occur from all these states in the case of AgTTC(TCBD)2 . Additionally, the high-energy CT states populate the low-lying triplet states. Systematic femtosecond pump-probe studies provided the ultimate proof for the occurrence of excited CT as a function of excitation wavelength followed by the efficient population of the triplet states. The present study brings out the significance of charge transfer in efficiently populating the triplet states in rather unusual copper and silver corroles carrying two TCBD entities.

Surveying the Evidence on Sustainable Intensification Strategies for Smallholder Agricultural Systems

Food demand is projected to increase significantly over the coming decades. Sustainable intensification (SI) is essential to meet this demand. SI is particularly important in smallholder systems, yet to date it remains unclear what the most promising SI strategies are to increase food production and farmer incomes at scale. We review the literature on SI to identify the most promising strategies, as manifest in replicated findings of favorable causal impacts. Adoption of improved cultivars generated the largest, most consistent, positive yield and economic outcomes. Two agroecological practices, push-pull systems and the System of Rice Intensification, also repeatedly led to large positive impacts. These strategies have considerable potential to scale to reach more than 50% of smallholder farmers who plant staple crops. Significant barriers to adoption remain, however, and identifying ways to overcome barriers to scale these successful strategies will be critical to meeting Sustainable Development Goals 1 and 2 by 2030.

Excitation Wavelength-Dependent Charge Stabilization in Highly Interacting Phenothiazine Sulfone-Derived Donor–Acceptor Constructs

Prolonging the lifetime of charge-separated states (CSS) is of paramount importance in artificial photosynthetic donor-acceptor (DA) constructs to build the next generation of light-energy-harvesting devices. This becomes especially important when the DA constructs are closely spaced and highly interacting. In the present study, we demonstrate extending the lifetime of the CSS in highly interacting DA constructs by making use of the triplet excited state of the electron donor and with the help of excitation wavelength selectivity. To demonstrate this, π-conjugated phenothiazine sulfone-based push-pull systems, PTS2-PTS6 have been newly designed and synthesized via the Pd-catalyzed Sonogashira cross-coupling followed by [2 + 2] cycloaddition-retroelectrocyclization reactions. Modulation of the spectral and photophysical properties of phenothiazine sulfones (PTZSO2) and terminal phenothiazines (PTZ) was possible by incorporating powerful electron acceptors, 1,1,4,4-tetracyanobutadiene (TCBD) and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD (exTCBD). The quadrupolar PTS2 displayed solvatochromism, aggregation-induced emission, and mechanochromic behaviors. From the energy calculations, excitation wavelength-dependent charge stabilization was envisioned in PTS2-PTS6, and the subsequent pump-probe spectroscopic studies revealed charge stabilization when the systems were excited at the locally excited peak positions, while such effect was minimal when the samples were excited at wavelengths corresponding to the CT transitions. This work reveals the impact of wavelength selectivity to induce charge separation from the triplet excited state in ultimately prolonging the lifetime of CCS in highly interacting push-pull systems.

Donor-Acceptor Tribenzotriquinacene-Based Molecular Wizard Hats Bearing Three ortho-Benzoquinone Units.

Two π-extended bay-bridged tribenzotriquinacenes ("TBTQ wizard hats") 12 and 16 bearing three mutually conjugated, alternating veratrole-type and ortho-benzoquinone units were synthesized. The electronic properties of these complementarily arranged, nonplanar push-pull systems are affected by the fusion with the rigid, C3 -symmetric TBTQ core to a different extent, as revealed by X-ray structural analysis, UV-vis spectroscopy and cyclovoltammetry. The combination of three quinone units within the original TBTQ core and three veratrole-type bay bridging units in 12 gives rise to a more efficiently π-conjugated chromophore, as reflected by the shallower shape of wizard hat and its absorption in the visible up to 750 nm in comparison to 16. Congener 12 contains an aromatic 18-π electron system in contrast to the cross-conjugated analog 16. X-ray structure analysis of the precursor dodecaether 15 revealed the formation of a cage-like supramolecular dimer, in which the peripheral dioxane-type ether groups interlace by twelve noncovalent C-H⋅⋅⋅⋅⋅O bonds.