Donor Substituents Research Articles

Tuning of environment-sensitive 3-hydroxychromone fluorophores based on strong donor substituents in positions 2 or 7

We have synthesized a series of environmentally sensitive fluorophores based on 3-hydroxychromone with systematically varied aromatic groups at positions 2 and 7. The two families of 2,7-diaryl-3-hydroxychromones were synthesized using Suzuki coupling from the corresponding 2-aryl-7-bromo-3-hydroxychromones. These chromophores exhibit a dual fluorescent emission and a strong response to changes in environmental polarity in organic solvents. Both experimental determination and calculations of dipole moment changes show stronger charge transfer in compounds with an electron donor group at position 7 compared to position 2. Their emission is almost totally quenched in the aqueous medium, while the increase in quantum yield upon binding to biological molecules serves as a useful characteristic. Particularly, compounds with strong donors in position 7 are sensitive to diverse lipid environments, whereas those with strong donors in position 2 have different emission profiles for distinct protein interactions. The complex behavior of the probes was evaluated using spectral phasor analysis. Altogether, these novel families of probes may help monitor several biological processes in vitro and in cell cultures.

Heterophenoquinones: Tuning Optoelectronics and Electrochromicity.

We report the synthesis and optoelectronic properties of 16 thiophene-based heterophenoquinones. These compounds were accessed in a convergent and modular approach, allowing for their efficient synthesis. Tuning of the optical band gap was achieved through π-extension by annulation of a benzene or tropone moiety to the thiophene, oxidation, change of the heteroatom or by attachment of a donor substituent to the thiophene core. The resulting compounds display intense colors covering the entire visible spectrum. We identified structure-property relationships and their impact on the HOMO and LUMO levels. Additionally, these materials change color upon reduction and according to in situ ultraviolet-visible-near infrared (UV-vis-NIR) and electron paramagnetic resonance (EPR) spectro-electrochemistry, they are promising electrochromes with cathodic color changes. Seven different electrochromic devices were constructed which all displayed a change in color upon reduction, demonstrating the potential of these new dyes in for example tintable glass.

Twisted intramolecular charge‐transfer state of trans‐3‐(N,N‐Dimethylamino)‐4'‐cyanostilbene: The C−C bond twisting

AbstractWhether a twisted intramolecular charge‐transfer (TICT) state is formed is an important issue for understanding the fluorescence properties of a push‐pull organic dye. Here we report a position effect of the donor substituent on the TICT state formation of aminostilbenes: namely, trans‐3‐(N,N‐dimethylamino)‐4′‐cyanostilbene (mDCS) behaves differently from its TICT‐free para isomer DCS and forms a TICT state in acetonitrile (MeCN). The TICT state of mDCS also differs from that of many previously reported aminostilbenes by twisting a C−C bond instead of a C−N bond. In addition, among the ring‐bridged model compounds mDCS‐N, mDCS‐C1, and mDCS‐C2, we observed an unusual electronic effect of the ring‐bridging in mDCS‐C2 that mitigates the impact of the TICT state on the fluorescence properties. Both the C−C bond twisting in mDCS and the ring‐bridging electronic effect in mDCS‐C2 provide new insights into the TICT chemistry of aminostilbenes.

Anthracene derivatives with hot exciton and TTA process for high-efficiency organic light-emitting diodes

Organic fluorophores with unique photophysical properties that converting the triplet excitons to singlet excitons, are desired to improve the efficiencies of organic light-emitting diodes (OLEDs). Here, two new anthracene-based emitters pipdAnCz and pipdAnTPA, with proper donor and acceptor substituents are designed and synthesized. The theoretical calculation and experimental results demonstrate that both pipdAnCz and pipdAnTPA possess hot exciton and triplet-triplet annihilation (TTA) characteristics, which can convert the triplet excitons to singlet excitons from the high-lying triplet energy levels (Tn) and the lowest triplet energy level (T1) respectively. Due to its relative higher photoluminescence quantum yields (PLQYs), the pipdAnTPA based non-doped device achieved a maximum external quantum efficiency (EQEmax) of 6.43% with an exciton utilization efficiency (EUE) of 72%. Further device physics study reveal that the hot exciton process is the dominant mechanism, assisted by TTA process, to convert the triplet excitons, especially for the pipdAnTPA based device.

Synthesis and Chemistry of 1,2,4,3-Triazaphosphole Derivatives

Abstract: This review describes the progress made during the last fifty years in the synthesis and chemistry of 1,2,4,3 triazaphospholes. This class of compounds has attracted tremendous homogeneous catalysis and interest in molecular materials science. These fascinating phosphorus heterocycles have conjugated π systems with high degrees of aromaticity. 1,2,4,3- Triazaphospholes can be designed through [3+2] cyclocondensation between functionalized hydrazines with phosphonoimidates that allow the incorporation of additional donor substituents into specific positions of the phosphorus heterocycle. In addition, [4+1] cyclocondensation between functionalized amidrazones and active phosphorus reagents is the most synthetically accessible method. The used strategies facilitated synthetic access to a completely new set of triazaphospholes leading to a much broader scope for potential applications. 1,2,4,3-triazaphospholes displayed reactivity towards a variety of reagents. The phosphorus is particularly prone to undergo oxidative 1,1-addition. Protic reagents such as alcohols, phenols, and amines can be added across the P=N bond of 2H-1,2,4,3-triazaphospholes to yield the dihydro-1,2,4,3-triazaphosphole derivatives. 1H- and 2H-1,2,4,3- triazaphospholes reacted with alcohols, ammonia and amines in the presence of sulfur or selenium to form dihydro- 1,2,4,3-triazaphosphole 3-chalcogenides. The appropriate difunctional reagents such as glycols, 2-azido alcohols and phenol with a heterodiene function in the ortho position reacted with 2H-1,2,4,3-triazaphospholes to yield products formed via 1,2-addition on P=N bond. Similar behavior is shown by 2-hydroxyacetophenone and 2- hydroxy-benzophenone. 2H-1,2,4,3-Triazaphospholes reacted with acetylenes to form [3+2] cycloadducts; the latter change to 1,2,3-diazaphospholes. [4+1] Cycloadditions occurred with α-diimines, azodicarboxylic esters, and 1,2-diketones; in the latter two cases, the resulting products dimerize.

Improved GNNs for Log D7.4 Prediction by Transferring Knowledge from Low-Fidelity Data

The n-octanol/buffer solution distribution coefficient at pH = 7.4 (log D7.4) is an indicator of lipophilicity, and it influences a wide variety of absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties and druggability of compounds. In log D7.4 prediction, graph neural networks (GNNs) can uncover subtle structure-property relationships (SPRs) by automatically extracting features from molecular graphs that facilitate the learning of SPRs, but their performances are often limited by the small size of available datasets. Herein, we present a transfer learning strategy called pretraining on computational data and then fine-tuning on experimental data (PCFE) to fully exploit the predictive potential of GNNs. PCFE works by pretraining a GNN model on 1.71 million computational log D data (low-fidelity data) and then fine-tuning it on 19,155 experimental log D7.4 data (high-fidelity data). The experiments for three GNN architectures (graph convolutional network (GCN), graph attention network (GAT), and Attentive FP) demonstrated the effectiveness of PCFE in improving GNNs for log D7.4 predictions. Moreover, the optimal PCFE-trained GNN model (cx-Attentive FP, Rtest2 = 0.909) outperformed four excellent descriptor-based models (random forest (RF), gradient boosting (GB), support vector machine (SVM), and extreme gradient boosting (XGBoost)). The robustness of the cx-Attentive FP model was also confirmed by evaluating the models with different training data sizes and dataset splitting strategies. Therefore, we developed a webserver and defined the applicability domain for this model. The webserver (http://tools.scbdd.com/chemlogd/) provides free log D7.4 prediction services. In addition, the important descriptors for log D7.4 were detected by the Shapley additive explanations (SHAP) method, and the most relevant substructures of log D7.4 were identified by the attention mechanism. Finally, the matched molecular pair analysis (MMPA) was performed to summarize the contributions of common chemical substituents to log D7.4, including a variety of hydrocarbon groups, halogen groups, heteroatoms, and polar groups. In conclusion, we believe that the cx-Attentive FP model can serve as a reliable tool to predict log D7.4 and hope that pretraining on low-fidelity data can help GNNs make accurate predictions of other endpoints in drug discovery.

Effect of Substituents with the Different Electron-Donating Abilities on Optoelectronic Properties of Bipolar Thioxanthone Derivatives.

The synthesis and optoelectronic properties of four simple-structure thioxanthone derivatives employing thioxanthone as an acceptor unit, coupled with moieties having very different electron-donating abilities such as phenoxazine, 3,6-di-tert-butylcarbazole, 3,7-di-tert-butylphenothiazine, or 2,7-di-tert-butyl-9,9-dimethylacridane, are reported. The compounds form molecular glasses with glass transition temperatures reaching 116 °C. Ionization potentials of the compounds estimated by photoelectron emission method range from 5.42 to 5.74 eV. Thioxanthone derivatives containing 3,6-tert-butylcarbazole or 2,7-di-tert-butyl-9,9-dimethylacridane moieties with weak electron-donating strengths were characterized by bipolar charge transport with relatively close hole and electron mobility values of 6.8 × 10-5/2.4 × 10-5 and 3.1 × 10-5/4.6 × 10-6 cm2/(V s) recorded at 3.6 × 105 V/cm. The other compounds demonstrated hole-transporting properties. The films of thioxanthones containing phenoxazine or 2,7-di-tert-butyl-9,9-dimethylacridane moieties showed efficient thermally activated delayed fluorescence with a photoluminescence quantum yield of up to 50% due to the solid-state luminescence enhancement. Organic-light-emitting diodes containing the synthesized compounds as emitters showed very different external quantum efficiencies (0.9-10.3%) and blue, sky blue, green, or yellow electroluminescence colors, thus reflecting the effects of donor substituents.

SYNTHESIS AND ABSORPTION SPECTRA OF INDOTRICARBOCYANINE DYES WITH ELECTRON-DONATING GROUPS IN THE MESO-POSITION OF THE POLYMETHINE CHAIN

Recently, a large number of studies have been dedicated to chemistry and physical stu­dies of polymethine dyes, especially to the functio­na­lized symmetrical heptamethinecyanines based on the indole derivatives. Due to their unique and versatile spectral properties, which lie in the near infrared region (NIR), meso-substituted indotricarbocyanine dyes are widely used in various physical and biological fields. In the present work, we have developed methods of synthesis of a series of indotricarbocyanine dyes with di- and trimethylene bridging groups in the γ,γ'-positions and donor substituents in the meso-position of the polymethine chromophore and studied their effects on the spectral properties of the dyes. The obtained data indicated that the change of the substituent in the meso-position of the chromophore and the presence of a poly­me­thylene bridging groups allow to vary signi­ficantly the absorption maxima of the synthesized indoheptamethinecyanine dyes without altering the length of the polymethine chain. It was shown that the electron-donating nitrogen-containing substituents lead, according to the Forster-Dewar-Knott rule, to a hypsochromic shifts of the absorption maxima. However, it was found that the methoxy group in the meso-position of the polymethine chromophore in some cases exhibited unexpected "acceptor" properties due to a certain steric hindrance, resulting in a red shift of the absorption band, in contrast to the other donor substituents. Additionally, the effects of the insertion of di- and trimethylene bridging groups to the polymethine chain of the cyanine dyes on their spectral properties were studied. The synthesized meso-substituted indotricarbocyanines demonstrated significant solvatochromism and spectral properties that lie in the red and near-infrared regions.

Reducing Efficiency Roll‐Off in Multi‐Resonant Thermally Activated Delayed Fluorescent OLEDs through Modulation of the Energy of the T2State

AbstractThe S1state and high‐lying triplet excited states (ΔES1Tn) offer insight into clarifying the mechanism of efficiency roll‐off of organic light‐emitting diodes (OLEDs). However, experimental detection of the ΔES1Tnis challenging due to Kasha's rule. Here, two emitters,PhCz‐O‐DiKTaandPhCz‐DiKTa, showing multi‐resonant thermally activated delayed fluorescence (MR‐TADF) are reported. By modulating the conjugation between the MR‐TADFDiKTaemissive center and donor substituent, emission directly from the T2state is for the first time observed in MR‐TADF emitters. Single crystal and reduced density gradient analyses reveal the origin of the reduced observed concentration‐quenching results from weak CH···π and slipped π···π stacking interactions, which suppress nonradiative transitions. Theoretical and photophysical investigations reveal that the ΔES1T2difference influences the reverse intersystem crossing rate. The OLEDs employingPhCz‐O‐DiKTaandPhCz‐DiKTaas emitters show maximum external quantum efficiencies (EQEmax) of over 20%, but very different efficiency roll‐off behavior (54.5% vs 13.6% at 100 cd m−2). Thus, this design provides a possible solution to mitigating device efficiency roll‐off by designing MR‐TADF emitters with degenerate S1and T2states.

Molecular Modeling, Docking, and QSAR Studies on A Series of N-arylsulfonyl-N-2-pyridinyl-piperazines Analogs Acting as Anti-Diabetic Agents

The Molecular structure of compounds contains a lot of information that can be used further. A classical Quantitative Structure Activity Relationship (QSAR) method was used to decode that information based on the descriptors. The study was performed on a mono-substituted series of Glucokinase-Glucokinase regulatory protein inhibitors (GK-GKRP/GCKR). A sequential application of the statistical method, both linear and nonlinear, has been used in the study which includes Multiple Linear Regression (MLR), Partial Least Square (PLS), and Artificial Neural Network (ANN). The developed model was validated using various statistical methods to evidently prove its reliability and precision. This knowledge will be used to design a new compound. Docking studies will be performed to establish the binding pattern of the designed compound. The prophetic power and robustness of the model containing 26 compounds in the training set were proven by the various statistical parameter s value: 0.30, F-value: 41.8, r: 0.94, r2: 0.88, r2CV: 0.77. The model gives insight into the various descriptors that are selected for the present study. The present study not only shows the contribution of various substituents in the biological activity but also indicates the changes that can be done to design the new potent molecules with more selectivity and less toxicity. HIGHLIGHTS The enzyme glucokinase (GCK) is responsible for maintaining the body's normal glucose homeostasis. Hypertriglyceridemia, hyperinsulinemia, and T2D are all triggered by GCK dysfunction or dysregulation An inhibitor of the glucokinase enzyme (GCK), which is only present in hepatocytes and is in charge of glucose metabolism, is encoded by the glucokinase regulator (GCKR) gene The designed model gives insight into the various descriptors that are selected for the present study. The present study not only shows the contribution of various substituents in the biological activity but also indicates the changes that can be done to design the new potent molecules with more selectivity and less toxicity Small compounds have been discovered that specifically bind to GKRP and lower blood sugar levels GRAPHICAL ABSTRACT

Luminescent furo[2,3-c]isoquinolines as fluorophores - Tuning the luminophore by donor substitution

A new library of the uncommon furo[2,3-c]isoquinoline scaffold has been synthesized by coupling the Ugi multicomponent reaction with a complex one-pot Pd-mediated double cyclization. The highly convergent and diversity-oriented approach has been exploited to introduce substituents with electron donor properties directly linked to the scaffold in the most representative positions 1 and/or 8. Moreover, the influence of an aromatic ring used as spacer between the scaffold and the electron donor substituent, as well as the substitution of the phenyl substituent in position 1 with a thiophene, on the photophysical properties have been investigated. Upon UV excitation part of the new molecules are intensively blue luminescent but for an amino donor substituent a significant switch to green emitters has been observed even upon eyesight. The electronic structure has been semiquantitatively rationalized by DFT and (TD)DFT calculations.

Lactam node as a two-fold functional unit for achieving highly efficient and tunable dual-state emitters

Although custom design offers an opportunity for synthesizing molecules with desired emission characteristics, compared with single-state emission, underdeveloped methodologies pose a significant challenge to accessing and further tailoring of dual-state emission. Herein, we report 1,8-naphtholactam (Np) and its derivatives, which not only function as efficient dual-state emitters but also as excellent building blocks for tunable dual-state emitters. By adjusting the π-conjugated donor substituent, bright emission from cyan to red can be facilely tailored in both solution and the solid state, resulting in an approximative full-color emission. Structural analysis reveals that the lactam group of Np works as a two-fold functional unit, simultaneously guaranteeing molecular rigidity for solution emission and hydrogen-bond-modulated packing without detrimental long-range π-π stacking for solid emission. Theoretical calculations corroborate the experimental results and efficient red bioimaging of Human hepatocellular carcinomas (HepG2) cells is achieved after the incubation with an Np derivative. Therefore, our lactam substitution strategy is a new route suitable for achieving efficient and tunable dual-state emitters.

Intramolecular OHO Hydrogen Bonding in Dibenzoylmethane Enol: Raman Spectroscopic and Quantum Chemical Study

In the present work, the intramolecular O-H···O hydrogen bonding in 3-hydroxy-1,3-diphenylprop-2-en-1-one (keto-enol form of dibenzoylmethane, DBM) was investigated. For this purpose, the Raman spectra of polycrystalline samples of ordinary (H-DBM) and deuterated (D-DBM) 3-hydroxy-1,3-diphenylprop-2-en-1-one in the temperature range of 5–300 K were measured. It was found that low-temperature hydrogen bonding is extremely strong, the proton and deuteron are located in the midpoint of the O···O segment, and their ground and first excited vibrational states are located above the barrier U0 between the local minima. The vibrational frequencies, in this case, are 1543 and 1709 cm−1 for the proton and 1045 and 1087 cm−1 for the deuteron. As the temperature rises and the barrier height increases in H-DBM, the zero-point vibrational state of the proton begins to move into one of the local minima at T > 50 K, while the excited state remains in the broad single-well potential. The same is observed in D-DBM, but with a significant temperature delay. Compounds with donor (−OCH3) and acceptor (−NO2) substituents in the phenyl ring were also synthesized and their spectra were obtained. Both results confirm existing ideas about the nature of the extremely strong hydrogen bond. The quantum-chemical calculation of the vibrational spectrum of H-DBM and D-DBM is consistent with the experimental results.

Effect of Chlorine Substituents on the Photovoltaic Properties of Monocyanated Quinoxaline-Based D–A-Type Polymers

A string of monocyanated quinoxaline (Qx)-based D-A-type polymers systematically decorated with electron-attracting chlorine (Cl) atoms was created for use in non-fullerene polymer solar cells (PSCs). First, coupling of the benzodithiophene (BDT) donor and Qx acceptor with the strong electron-attracting cyano (CN) unit at its 5-position yielded the monocyanated reference polymer PB-CNQ. Subsequently, the additional Cl atoms were separately or simultaneously incorporated into the thiophene side groups of the BDT donor and Qx acceptor to create other objective polymers, PBCl-CNQ, PB-CNQCl, and PBCl-CNQCl. The Cl substituents on the BDT donor and Qx acceptor are represented by the names of the polymers. Owing to the favorable contributions of Cl substituents, the inverted-type non-fullerene PSCs based on partially chlorinated PBCl-CNQ (12.80%) and PB-CNQCl (13.93%) exhibited better power conversion efficiencies (PCEs) than the device based on unchlorinated reference PB-CNQ (11.19%). However, a significantly reduced PCE of 9.84% was observed for the device based on PBCl-CNQCl, in which Cl atoms were loaded on both the BDT donor and Qx acceptor at the same time. Hence, these results reveal that optimization of the number and position of Cl substituents in monocyanated Qx-based polymers is essential for enhancing their photovoltaic nature through the synergistic effects between two strong electron-attracting CN and Cl substituents.

Solvent-Controlled Photoswitching of Azobenzene: An Excited State Shuttle.

Light controlled excited state trans-cis isomerization process is a key to the development of conversion of light energy to mechanical motion at the molecular level. Considerable efforts have been made in tuning the isomerization process with electron donor and acceptor substituents by altering the excited state reaction coordinate. Here, we report a two novel push-pull series of para-diethylamino (DEA) and diphenylamino (DPA) substituted (E)-4'-((4-(diethylamino)phenyl)diazenyl)-N,N-diphenyl-[1,1'-biphenyl]-4-amine (1) and (E)-4'-((4-(diphenylamino)phenyl)diazenyl)-N,N-diphenyl-[1,1'-biphenyl]-4-amine (2). Compound 1 and 2 undergoes both photochemical and photophysical excited state deactivation pathways which can be controlled by varying the solvent polarity. These structural motifs of 1 and 2 would undergo torsional motions upon excitation to exhibit either trans → cis photoisomerization or to form a twisted intramolecular charge transfer state and both the process originates from the same excited state and competes with each other. Thus, alternations in the surrounding environment such as solvent polarity, solution viscosity, and protonation were employed to understand the preferential excited state deactivation pathway and thereby these systems could be employed as a new class of azobenzene-based luminescent photochromic molecules. For instance, in nonpolar solvent, toluene photoisomerization is preferred over TICT, but polar solvent, ethanol preferentially stabilizes the TICT state by virtue of N-C rotation which renders the energy barrier unfavourable for photoisomerization. The photostationary state of 1 in toluene is predominantly the Z isomer, whereas in ethanol E isomer is nearly two-fold higher than the Z isomer. These feature sets up a new approach towards the construction of multinary molecular switches and subsequent development in diverse fields.

N-Phosphinoamidinato Silylene- and Phosphine-Borylborylene Complexes.

This work describes a straightforward method to synthesize a borylborylene without proceeding via the rearrangement of a diborene. An amidinato amidosilylene [LSiNMe2] (L = PhC(NtBu)2) and PMe3 were reacted with an N-phosphinoamidinato diborane 1 and KC8 to form a stable silylene-borylborylene 2 and a persistent phosphine-borylborylene 3, respectively. Compound 2 is stable as the borylene center is well stabilized by the silylene donor and boryl substituent, whereas compound 3 is unstable in solution due to labile PMe3. The latter was illustrated by reacting compound 3 with Ar'NC (Ar' = 2,6-Me2C6H3), where Ar'NC displaced PMe3 and inserted into the N-phosphinoamidinate ligand and B-B bond to form compound 4.

Effects of donor and acceptor substituents on the photophysics of 4-ethynyl-2,1,3-benzothiadiazole derivatives.

The present work explores the photophysical, electrochemical, and fluorescence polarization properties of a group of π-conjugated phenylethynyl-2,1,3-benzothiadiazole derivatives (BTDs) bearing different electron-donating (ED) or electron-withdrawing (EW) substituents at the para position of the phenylethynyl moiety. The BTDs were synthesized through the Sonogashira cross-coupling reaction between 4-bromo-2,1,3-benzothiadiazole and the respective para-substituted phenylethynyl derivatives. The BTDs with the EW-substituents show relatively weak solvatochromic behavior, while the BTDs with the strong ED-substituents like methoxy and N,N-dimethylamino-based substituents (BTDPhOMe and BTDPhNMe2) exhibit a pronounced solvatochromic behavior. The change in dipole moments in the excited states of the derivatives was calculated using Lippert-Mataga plots. The conclusions drawn on the spectral behavior of the molecules could be rationalized by TD-DFT calculations involving electron density difference (EDD) maps that correlate with the ICT characteristics of the molecules. The experimental and theoretical calculations reveal that the BTDs with the strong ED-substituents (strong push-pull type BTDs) have a strong ICT character in the excited state. These strong push-pull type BTDs show high fluorescence quantum yield (ΦF) in apolar solvents and low ΦF in polar solvents. In contrast, the BTDs with the weak ED-substituents (weak push-pull type BTDs) and EW-substituents (pull-pull type BTDs) have a weaker ICT character with low ΦF in apolar and high ΦF in polar solvent media. There is good a agreement among the HOMO-LUMO band gaps obtained from absorption spectroscopy and electrochemical studies and theoretical calculations. The fluorescence anisotropy measurement in the glycerol medium shows that the studied BTDs generally exhibit higher sensitivity towards microviscosity than the traditional DPH fluorescence anisotropy probe.

How do donor and acceptor substituents change the photophysical and photochemical behavior of dithienylethenes? The search for a water-soluble visible-light photoswitch.

Dithienylethenes are a type of diarylethene and they constitute one of the most widely studied classes of photoswitch, yet there have been no systematic studies of how electron-donor or -acceptor substituents affect their properties. Here we report eight dithienylethenes bearing push-push, pull-pull and push-pull substitution patterns with different lengths of conjugation in the backbone and investigate their photophysical and photochemical properties. Donor-acceptor interactions in the closed forms of push-pull dithienylethenes shift their absorption spectra into the near-infrared region (λmax ≈ 800 nm). The push-pull systems also exhibit low quantum yields for photochemical electrocyclization, and computational studies indicate that this can be attributed to stabilization of the parallel, rather than anti-parallel, conformations. The pull-pull systems have the highest quantum yields for switching in both directions, ring-closure and ring-opening. The chloride salt of a pull-pull DTE, with alkynes on both arms, is the first water-soluble dithienylethene that can achieve >95% photostationary state distribution in both directions with visible light. It has excellent fatigue resistance: in aqueous solution on irradiation at 365 nm, the photochemical quantum yields for switching and decomposition are 0.15 and 2.6 × 10-5 respectively, i.e. decomposition is more than 5000 times slower than photoswitching. These properties make it a promising candidate for biological applications such as super-resolution microscopy and photopharmacology.

Influence of crystal structure and composition on optical and electronic properties of pyridinium-based bismuth iodide complexes.

This study investigates the impacts of structure and composition on the optical and electronic properties of a series of pyridinium-based bismuth iodide complexes. Organic substrates with various functional groups, such as 4-aminopyridine (4-Ampy), 4-methylpyridine (4-Mepy), 4-dimethylaminopyridine (4-Dmapy), and 4-pyridinecarbonitrile (4-CNpy) with different electron-donating and electron-withdrawing groups at the para position of the pyridine ring were employed. Crystallographic analysis reveals various bismuth iodide structures, including 1D chains and discrete 0D motifs. The optical band gap of these materials, identified via diffuse reflectance spectroscopy (DRS) and verified with density functional theory (DFT) calculations, is influenced by the crystal packing and stabilising interactions. Through a comprehensive analysis, including Hirshfeld surface (HS) and void assessment, the study underscores the influence of noncovalent intermolecular interactions on crystal packing. Spectroscopic evaluations provide insights into electronic interactions, elucidating the role of electron donor and acceptor substituents within the lattice. Thermogravimetric differential thermal analysis (TG-DTA) indicates structural stability up to 250 °C. Linear sweep voltammetry (LSV) reveals significant conductivity in the range of 10-20 mS per pixel at 298.15 K. X-ray absorption spectroscopy (XAS) at the Bi L3 edge indicates a similar oxidation state and electronic environment across all samples, underscoring the role of bismuth centres surrounded by iodides.

Back to the future: asymmetrical DπA 2,2'-bipyridine ligands for homoleptic copper(i)-based dyes in dye-sensitised solar cells.

Metal complexes used as sensitisers in dye-sensitised solar cells (DSCs) are conventionally constructed using a push-pull strategy with electron-releasing and electron-withdrawing (anchoring) ligands. In a new paradigm we have designed new DπA ligands incorporating diarylaminophenyl donor substituents and phosphonic acid anchoring groups. These new ligands function as organic dyes. For two separate classes of DπA ligands with 2,2'-bipyridine metal-binding domains, the DSCs containing the copper(i) complexes [Cu(DπA)2]+ perform better than the push-pull analogues [Cu(DD)(AA)]+. Furthermore, we have shown for the first time that the complexes [Cu(DπA)2]+ perform better than the organic DπA dye in DSCs. The synthetic studies and the device performances are rationalised with the aid of density functional theory (DFT) and time-dependent DFT (TD-DFT) studies.