Gold‐Catalyzed Cyclization of 1‐(Indol‐3‐yl)‐3‐alkyn‐1‐ols: Facile Synthesis of Diversified Carbazoles

Efficient cyclization of 1‐(indol‐3‐yl)‐3‐alkyn‐1‐ols in the presence of a cationic gold(I) complex, leading to annulated or specific substituted carbazoles, was observed. Depending on the reaction conditions and substitution pattern, divergent reaction pathways were discovered, furnishing diversified carbazole structures. Cycloalkyl‐annulated [b]carbazoles are obtained through 1,2‐alkyl migration of the metal‐carbene intermediates; cycloalkyl‐annulated [a]carbazoles are formed through a Wagner–Meerwein‐type 1,2‐alkyl shift; carbazole ethers are constructed through ring‐opening of the cyclopropyl group by nucleophilic attack of water or an alcohol.     

A Promising Candidate with D‐A‐A‐A Architecture as an Efficient Sensitizer for Dye‐Sensitized Solar Cells

A series of metal‐free organic dyes with electron‐rich (D) and electron‐deficient units (A) as π linkers have been studied theoretically by means of density functional theory (DFT) and time‐dependent DFT calculations to explore the effects of π spacers on the optical and electronic properties of triphenylamine dyes. The results show that Dye 1 with a structure of D‐A‐A‐A is superior to the typical C218 dye in various key aspects, including the maximum absorption (λ_max=511 nm), the charge‐transfer characteristics (D/Δq/t is 5.49 Å/0.818 e^?/4.41 Å), the driving force for charge‐carrier injection (ΔG_inject=1.35 eV)/dye regeneration (ΔG_regen=0.27 eV), and the lifetime of the first excited state (τ=3.1 ns). It is thus proposed to be a promising candidate in dye‐sensitized solar cell applications.     

Synthesis,alkali metal picrate extraction,and alkali metal cation binding selectivities of some new cage‐annulated polyoxamacrocyclic crown ethers

Five new cage‐annulated crown ethers, i.e., 4a, 4b, 6b, 11a, and 11b, have been synthesized and their respective alkali metal picrate extraction profiles along with that of a previously synthesized host molecule, 6a, have been obtained. These results are compared with the corresponding results obtained for electrospray ionization mass spectrometric (ESI‐MS) measurements of relative binding selectivities displayed by the same hosts toward a series of alkali metal chlorides. Among the crown‐5 hosts studied, 6a displays enhanced avidity toward complexation with K⁺ picrate in liquid‐liquid extraction experiments. Among the three crown‐6 hosts, 4b proved to be the best alkali metal picrate extractant and displayed significant levels of avidity toward complexation with the larger alkali metal cations (i.e., K⁺, Rb⁺, and Cs⁺). The trends in the picrate extraction and the ESI‐MS results obtained herein show several notable similarities and some differences. The similarities generally stem from size‐selective binding properties that are intrinsic to the different cavity sizes of the cage‐annulated macrocycles, whereas the differences reflect the important influence of solvation effects on the binding properties of the macrocycles.     

Photoinduced Charge Separation in a Donor–Spacer–Acceptor Dyad with N‐Annulated Perylene Donor and Methylviologen Acceptor

The first donor–acceptor species in which a strongly emissive N‐annulated perylene dye is connected to a methylviologen electron acceptor unit via its macrocyclic nitrogen atom, is prepared by a stepwise, modular procedure. The absorption spectra, redox behavior, spectroelectrochemistry and photophysical properties of this dyad and of its model species are investigated, also by pump–probe fs transient absorption spectroscopy. Photoinduced oxidative electron transfer from the excited state of the dyad, centered on the N‐annulated perylene subunit, to the appended methyviologen electron acceptor takes place in a few ps. The charge‐separated species recombines in 19 ps. Our results indicate that N‐annulated perylene can be connected to functional units by taking advantage of the macrocyclic nitrogen, an option never used until now, without losing their properties, so opening the way to new designing approaches.     

The Role of π Bridges in High‐Efficiency DSCs Based on Unsymmetrical Squaraines

A series of squaraine‐based sensitizers with various π bridges and anchors were prepared and examined in dye‐sensitized solar cells. The carboxylic anchor group was attached onto a squaraine dye through π bridges with and without an ethynyl spacer. DFT studies indicate that the LUMO is delocalized throughout the dyes, whilst the HOMO resides on the squaraine core. The dye that incorporates a 4,4‐di‐n‐hexyl‐cyclopentadithiophene group that is directly attached onto the π bridge, JD10 , exhibits the highest power conversion efficiency in a DSC; this result is attributed, in part, to the deaggregative properties that are associated with the gem‐di‐n‐hexyl substituents, which extend above and below the π‐conjugated dye plane. Dye JD10 demonstrates a power‐conversion efficiency of 7.3 % for liquid‐electrolyte dye‐sensitized solar cells and 7.9 % for cells that are co‐sensitized by another metal‐free dye, D35 , which substantially exceed the performance of any previously tested squaraine sensitizer. A panchromatic incident‐photon‐to‐current‐conversion efficiency curve is realized for this dye with an excellent short‐circuit current of 18.0 mA cm^?2. This current is higher than that seen for other squaraine dyes, partially owing to a high molar absorptivity of >5 000 M ^?1 cm^?1 from 400 nm to the long‐wavelength onset of 724 nm for dye JD10 .     

Benzimidazole‐indole‐chalcone connected methacrylate‐based side chain D‐π‐A polymer and its application in organic photovoltaics

Herein, we report four metal‐free organic polymethacrylates (In‐In‐BzI)PMA , (Ac‐In‐BzI)PMA , (TPA‐In‐BzI)PMA , and (Py‐In‐BzI)PMA with pendant chromophores donor‐π‐conjugated‐acceptor (D‐π‐A) molecular framework as photosensitizers for dye‐sensitized solar cells (DSSCs). In which the donor‐acceptor units are attached by an indole‐chalcone extending side chain to inhibit back electron transfer and charge recombination; the π‐linker component contains varied chalcone‐based substituents to enhance the sunlight‐harvesting ability of the solar device. Photon‐current cells based on the DSSC format were fabricated using the polymers as sensitizers. The DSSC device assembled using (TPA‐In‐BzI)PMA exhibits a considerably better IPCE peak and J–V response, with an overall power conversion efficiency of 3.70% under the illumination of AM 1.5G (100 mW cm^–2). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 997–1007     

Non‐classical Design of High‐Efficiency Sensitizers for Dye‐Sensitized Solar Cells

The dye regeneration step in a dye‐sensitized solar cell (DSSC) affects significantly the device efficiency. To be able to predict the dye regeneration efficiency by the electrolyte this paper provides a facile way to design high‐efficiency sensitizers for DSSC. This paper proposes, for the first time, a simple and ingenious way to identify the dye regeneration sites and their relative efficiencies when a specific electrolyte is used. Two steps are proposed to identify the dye regeneration sites and their relative regeneration efficiencies: (1) drawing all the resonance structures of the oxidized dye to determine the regeneration sites, and (2) choosing the most favored site for dye regeneration as the chemically softest (when the redox couple used is soft I⁻/I₃⁻ pair) and the least spatially hindered site. The regeneration sites identified by the resonance structures are consistent with the β‐LUSO (β lowest unoccupied spin orbital) distribution, which is generally used for identifying the dye regeneration sites, calculated with DT‐DFT theory. The relative dye regeneration efficiency and photovoltaic performance of both ruthenium and metal‐free organic dyes predicted by the method reported here are supported by experimental data and the proposed dye regeneration mechanism. Several types of dye molecules are used to demonstrate the correctness of this new tool. This non‐classical tool, which uses the well‐known chemical knowledge of the resonance structure and hard–soft acid–base principle, without any computer calculation or physicochemical measurement, provides a very simple and powerful tool to quickly conceive high‐efficiency sensitizers for DSSCs.     

N‐Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J‐ and H‐Aggregates

The unique self‐assembling features of N‐annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1 , in which no H‐bonding interactions are operative, corroborates the significance of long‐range van der Waals and dipole–dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N‐annulated PBI in 2 stimulates pathway differentiation to achieve up to three J‐type aggregates and a fourth H‐type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self‐assembly and the rich differentiation that N‐annulated PBIs exhibit, opening the door to new, complex, functional supramolecular materials.     

Regioselective Synthesis and Photophysical and Electrochemical Studies of 20‐Substituted Cyanine Dye–Purpurinimide Conjugates: Incorporation of NiII into the Conjugate Enhances its Tumor‐Uptake and Fluorescence‐Imaging Ability

We report herein a simple and efficient approach to the synthesis of a variety of meso‐substituted purpurinimides. The reaction of meso ‐ substituted purpurinimide with N‐bromosuccinimide regioselectively introduced a bromo functionality at the 20‐position, which on further reaction with a variety of boronic acids under Suzuki reaction conditions yielded the corresponding meso‐substituted analogues. Interestingly, the free base and the metalated analogues showed remarkable differences in photosensitizing efficacy (PDT) and tumor‐imaging ability. For example, the free‐base conjugate showed significant in vitro PDT efficacy, but limited tumor avidity in mice bearing tumors, whereas the corresponding Ni^II derivative did not produce any cell kill, but showed excellent tumor‐imaging ability at a dose of 0.3 μmol kg^?1 at 24, 48, and 72 h post‐injection. The limited PDT efficacy of the Ni^II analogue could be due to its inability to produce singlet oxygen, a key cytotoxic agent required for cell kill in PDT. Based on electrochemical and spectroelectrochemical data in DMSO, the first one‐electron oxidation (0.52 V vs. SCE) and the first one‐electron reduction (?0.57–0.67 V vs. SCE) of both the free base and the corresponding Ni^II conjugates are centered on the cyanine dye, whereas the second one‐electron reduction (?0.81 V vs. SCE) of the two conjugates is assigned to the purpurinimide part of the molecule. Reduction of the cyanine dye unit is facile and occurs prior to reduction of the purpurinimide group, which suggests that the cyanine dye unit as an oxidant could be the driving force for quenching of the excited triplet state of the molecules. An interaction between the cyanine dye and the purpurinimide group is clearly observed in the free‐base conjugate, which compares with a negligible interaction between the two functional groups in the Ni^II conjugate. As a result, the larger HOMO–LUMO gap of the free‐base conjugate and the corresponding smaller quenching constant is a reason to decrease the intramolecular quenching process and increase the production of singlet oxygen to some degree.     

Core‐Shell Structured Layered Lanthanide‐Organic Complexes with Stilbazolium‐type Dye Encapsulation for Multifunctional Performances

Host‐guest encapsulation of functional organic dye into a porous metal‐organic framework can give rise to the development of new functional materials. In this work, by intercalating the stilbazolium‐type dye (DEAST)I (4′‐diethylamino‐N‐methyl stilbazolium) into four lanthanide layered metal‐organic complexes (Ln‐LMOCs), i. e. {[Ln(BTB)(H₂O)₂]?3(DMF)?2(H₂O)}_n (Ln=La (1), Nd (2), Sm (3), Er (4)), four responsive (DEAST)I@Ln‐LMOC composites have been prepared, serving as multifunctional performance platform. The core–shell structures of (DEAST)I@Ln‐LMOC composites have been fully characterized by IR, UV/Vis, PXRD, SEM, TEM, TGA and ESR. Significantly, after intercalation of dyes, the (DEAST)I@Ln‐LMOC composites exhibit enhanced luminescent sensing properties in detecting Fe³⁺ with much higher water stabilities. The luminescent sensing behavior stems from the fluorescence resonance energy transfer (FRET) from the π‐electron‐rich BTB ligands to the Fe³⁺, and their higher water stabilities are induced by electrostatic interactions and lower porosity. Specially, the characteristic emissions of Sm³⁺ will not be affected after the encapsulation guest dyes, which provide a theoretical guide for the modulation of luminescence devices. Finally, better ion conductivities and diminished photocurrents can be achieved after the embedding of the functional organic dye. In all, the formation of (DEAST)I@Ln‐LMOC composites with core–shell structures can be utilized as a multifunctional platform with good stability.     

Tautomeric Switching and Metal‐Cation Sensing of Ligand‐Equipped 4‐Hydroxy‐/4‐oxo‐1,4‐dihydroquinolines

Novel 4‐hydroxyquinoline (4HQ) based tautomeric switches are reported. 4HQs equipped with coordinative side arms (8‐arylimino and 3‐piperidin‐1‐ylmethyl groups) were synthesized to access O‐ or N‐selective chelation of Zn²⁺ and Cd²⁺ ions by 4HQ. In the case of the monodentate arylimino group, O chelation of metal ions induces concomitant switching of phenol tautomer to the keto form in nonpolar or aprotic media. This change is accompanied by selective and highly sensitive fluorometric sensing of Zn²⁺ ions. In the case of the bidentate 8‐(quinolin‐8‐ylimino)methyl side arm, NMR studies in CD₃OD indicated that both Cd²⁺ and Zn²⁺ ions afford N chelation for 4HQ, coexisting with tautomeric switching from quinolin‐4(1H)‐one to quinolin‐4‐olate. In corroboration, UV/Vis‐monitored metal‐ion titrations in toluene and methanol implied similar structural changes. Additionally, fluorescence measurements indicated that the metal‐triggered tautomeric switching is associated with compound signaling properties. The results are supported by DFT calculations at the B3LYP 6‐31G* level. Several X‐ray structures of metal‐free and metal‐chelating 4HQ are presented to support the solution studies.     

Cyclometalated Ruthenium(II) Complexes Featuring Tridentate Click‐Derived Ligands for Dye‐Sensitized Solar Cell Applications

A series of heteroleptic bis(tridentate) Ru^II complexes featuring N^C^N‐cyclometalating ligands is presented. The 1,2,3‐triazole‐containing tridentate ligands are readily functionalized with hydrophobic side chains by means of click chemistry and the corresponding cyclometalated Ru^II complexes are easily synthesized. The performance of these thiocyanate‐free complexes in a dye‐sensitized solar cell was tested and a power conversion efficiency (PCE) of up to 4.0 % (J_sc=8.1 mA cm^?2, V_oc=0.66 V, FF=0.70) was achieved, while the black dye ((NBu₄)₃[Ru(Htctpy)(NCS)₃]; Htctpy=2,2′:6′,2′′‐terpyridine‐4′‐carboxylic acid‐4,4′′‐dicarboxylate) showed 5.2 % (J_sc=10.7 mA cm^?2, V_oc=0.69 V, FF=0.69) under comparable conditions. When co‐adsorbed with chenodeoxycholic acid, the PCE of the best cyclometalated dye could be improved to 4.5 % (J_sc=9.4 mA cm^?2, V_oc=0.65 V, FF=0.70). The PCEs correlate well with the light‐harvesting capabilities of the dyes, while a comparable incident photon‐to‐current efficiency was achieved with the cyclometalated dye and the black dye. Regeneration appeared to be efficient in the parent dye, despite the high energy of the highest occupied molecular orbital. The device performance was investigated in more detail by electrochemical impedance spectroscopy. Ultimately, a promising Ru^II sensitizer platform is presented that features a highly functionalizable “click”‐derived cyclometalating ligand.     

A High‐Performance Organic Field‐Effect Transistor Based on Platinum(II) Porphyrin: Peripheral Substituents on Porphyrin Ligand Significantly Affect Film Structure and Charge Mobility

Organic field‐effect transistors incorporating planar π‐conjugated metal‐free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H₂(OX)] (H₂OX=etioporphyrin‐I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H₂TBP=tetra‐(n‐butyl)porphyrin) as determined by single crystal X‐ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field‐effect transistors (FETs) made from thin films of all these metal‐free macrocycles and their metal derivatives show a p‐type semiconductor behavior with a charge mobility (μ) ranging from 10^?6 to 10^?1 cm² V^?1 s^?1. Annealing the as‐deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2×10^?1 cm² V^?1 s^?1, which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field‐effect transistors made from thin films of metal‐free macrocycles (except tetra‐(n‐propyl)porphycene) have significantly lower μ values (3.0×10^?6–3.7×10^?5 cm² V^?1 s^?1).     

Metal‐Free Dehydrogenative Diels–Alder Reactions of 2‐Methyl‐3‐Alkylindoles with Dienophiles: Rapid Access to Tetrahydrocarbazoles,Carbazoles, and Heteroacenes

An unprecedented strategy for in situ generation of indole‐based ortho‐quinodimethanes (oQDMs) from 2‐methyl‐3‐alkylmethylindoles by either a metal‐free DDQ‐ or BQ‐mediated dehydrogenative process was developed. These oQDMs were trapped by electron‐deficient dienophiles to provide a facile approach to synthetically valuable tetrahydrocarbazoles, carbazoles, and hetereoacenes. The salient features of this transformation include direct C(sp³) H bond functionalizations, readily available starting materials, metal‐free conditions, high efficiency, operational simplicity, and ease of scale‐up.     

Metal‐Free Dehydrogenative Diels–Alder Reactions of 2‐Methyl‐3‐Alkylindoles with Dienophiles: Rapid Access to Tetrahydrocarbazoles,Carbazoles, and Heteroacenes

An unprecedented strategy for in situ generation of indole‐based ortho‐quinodimethanes (oQDMs) from 2‐methyl‐3‐alkylmethylindoles by either a metal‐free DDQ‐ or BQ‐mediated dehydrogenative process was developed. These oQDMs were trapped by electron‐deficient dienophiles to provide a facile approach to synthetically valuable tetrahydrocarbazoles, carbazoles, and hetereoacenes. The salient features of this transformation include direct C(sp³)? H bond functionalizations, readily available starting materials, metal‐free conditions, high efficiency, operational simplicity, and ease of scale‐up.     

Metal‐Free‐Mediated Oxidation Aromatization of 1,4‐Dihydropyridines to Pyridines Using Visible Light and Air

A metal‐free and environmentally friendly aerobic aromatization photosensitized by organic dye eosin Y bis(tetrabutyl ammonium salt) (TBA‐eosinY) has been developed. With the aid of K₂CO₃, the aerobic catalytic system converts 1,4‐dihydropyridines to their corresponding pyridine derivatives efficiently under visible light irradiation (λ=450 nm) at room temperature.     

Dyes and Redox Couples with Matched Energy Levels: Elimination of the Dye‐Regeneration Energy Loss in Dye‐Sensitized Solar Cells

In dye‐sensitized solar cells (DSSCs), a significant dye‐regeneration force (ΔG_reg⁰≥0.5 eV) is usually required for effective dye regeneration, which results in a major energy loss and limits the energy‐conversion efficiency of state‐of‐art DSSCs. We demonstrate that when dye molecules and redox couples that possess similar conjugated ligands are used, efficient dye regeneration occurs with zero or close‐to‐zero driving force. By using Ru(dcbpy)(bpy)₂²⁺ as the dye and Ru(bpy)₂(MeIm)₂^3+//2+ as the redox couple, a short‐circuit current (J_sc) of 4 mA cm^?2 and an open‐circuit voltage (V_oc) of 0.9 V were obtained with a ΔG_reg⁰ of 0.07 eV. The same was observed for the N3 dye and Ru(bpy)₂(SCN)₂^1+/0 (ΔG_reg⁰=0.0 eV), which produced an J_sc of 2.5 mA cm^?2 and V_oc of 0.6 V. Charge recombination occurs at pinholes, limiting the performance of the cells. This proof‐of‐concept study demonstrates that high V_oc values can be attained by significantly curtailing the dye‐regeneration force.     

Molecular design of organic dyes with diketopyrrolopyrrole for dye‐sensitized solar cell: A theoretical approach

Three designed metal‐free dyes based on 3‐(10‐butyl‐8‐(methylthio)‐10H‐phenothiazin‐3‐yl)‐2‐cyanoacrylic acid (V5) are investigated by density functional theory (DFT) and time‐dependent DFT to improve the efficiency of V5‐based solar cell devices. We have studied the geometrical structures, excitations, electronic structures, and conduction band shift caused by dye adsorption. The results indicate that the designed dyes have several merits compared with V5 including: (i) smaller energy band gaps and the LUMO closer to conduction band of TiO₂; (ii) wider absorption spectra and higher oscillator strength; (iii) larger dipole moment that lead to higher V_oc value. Our work suggests that the modification of π‐bridge with diketopyrrolopyrrole unit is very effective for designing novel metal‐free dyes with improved performance for dye‐sensitized solar cells (DSSCs). These findings are expected to provide a bright way to design new efficient metal‐free organic DSSCs. © 2014 Wiley Periodicals, Inc.     

Intramolecular Metal‐Free Oxidative Aryl–Aryl Coupling: An Unusual Hypervalent‐Iodine‐Mediated Rearrangement of 2‐Substituted N‐Phenylbenzamides

Hypervalent‐iodine‐mediated oxidative coupling of the two aryl groups in either 2‐acylamino‐N‐phenyl‐benzamides or 2‐hydroxy‐N‐phenylbenzamides, with concomitant insertion of the ortho‐substituted N or O atom into the tether, has been described for the first time. This unusual metal‐free rearrangement reaction involves an oxidative C(sp²)? C(sp²) aryl–aryl bond formation, cleavage of a C(sp²)? C(O) bond, and a lactamization/lactonization. Furthermore, unsymmetrical diaryl compounds can be easily obtained by removing the tether within the cyclized product.     

7‐Azacinnolin‐4(1H)‐one preparation and NMR studies of tautomery

As part of our current investigations of nitropyridines, we hereby report the preparation of a new annulated heterocycle by C‐azo coupling. Thus, the azacinnoline, pyrido[3,4‐c]pyridazin‐4(1H)‐one (38%), was prepared from 4‐acetyl‐3‐aminopyridine via diazotization. ¹H, ¹³C, and ¹⁵N NMR spectroscopic investigations revealed that the azacinnoline exclusively exists in the NH‐keto tautomeric form in DMSO‐d₆, CD₃OD, and D₂O. J. Heterocyclic Chem., (2011).