Bathochromic Research Articles

High‐Efficiency Near‐Infrared Iridium(III) Complexes with Tailored Ligands for Solution‐Processed OLEDs with Maximum EQE of 3.75% at 830 nm

AbstractThe development of highly efficient pure near‐infrared (NIR) emitting organic materials with emission beyond 800 nm is extremely challenging due to the limitation of the energy gap law. Herein, three efficient NIR emitting iridium(III) complexes are developed adopting pyrido[3,4‐b]pyrazine derivatives as the cyclometalated C^N ligands, namely (Epptt)2Iracac (1), (pptt)2Iracac (2), and (ppCz)2Irtmd (3). Due to the enhanced donor–acceptor interaction inside the ligand, the conjugation‐extended and electron‐richer N‐phenylcarbazole unit at the C‐part of the ligands endows complex 3 with a large bathochromic shift of emission peak from 796 to 862 nm in toluene solution, compared with thieno[3,2‐b]thiophene C‐part in complex 2. The solution‐processed OLEDs based on complex 3 achieved a record high maximum external quantum efficiency of 3.75% and low efficiency roll‐off with the emission peak at 830 nm, a champion efficiency in the Ir(III) based OLEDs with emission peak exceeding 800 nm. This work opens a new avenue for the development of high‐efficiency pure NIR organic emitters based on Ir(III) complexes for various applications.

Dithieno[3,2-b; 2',3'-f]phosphepinium-Based Near-Infrared Fluorophores: px-π* Conjugation Inherent to Seven-Membered Phosphacycles.

Positively charged phosphorus-containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium-containing five- or six-membered-ring compounds have been reported, the seven-membered-ring phosphepinium have not been fully studied yet. In this study, dithieno[3,2-b; 2',3'-f]phosphepinium ions containing electron-donating aminophenyl groups were synthesized. An X-ray crystallographic analysis of the resulting donor-acceptor-donor dyes revealed a bent conformation of the central seven-membered ring. These compounds exhibit fluorescence in the near-infrared region with a bathochromic shift of ca. 70 nm compared to a phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. A theoretical study revealed that the phosphepinium skeleton is highly electron-accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5-hexatriene moiety. Due to the lower-lying px orbital in the phosphonium moiety compared to that of the phosphine oxide and the bent conformation of the seven-membered ring, the phosphepinium ring permits effective px-π* conjugation. A large structural relaxation with a contribution of a quinoidal resonance structure is suggested in the excited state, which should be responsible for the bright emission with a large Stokes shift.

Влияние цетиламина на спектры поглощения и протолитические свойства люмогаллиона и магнезона ХС

The interaction of monoazo compounds lumogallion (LG) and magnezon HS (MHS) with cetylamine (CA) in a wide pH range has been studied using a spectrophotometric method.It has been shown that the formation of ionic associates of CA under the interaction of its cation with sulfo group of azo compounds in the pH range 1–4 does not change the electronic absorption spectra of the azodyes. The interaction of CA at dissociated OH groups conjugated with the π-system of the azo compounds leads to a bathochromic shift in the maximum of the absorption spectrum of the corresponding ionic form of the reagents by 15 and 30 nm for the doubly and triply charged forms of LG, respectively, and by 50 nm for the doubly charged form of MHS. The shift in the maximum of the absorption spectrum is accompanied by the shift in the apparent pK value of the reagents by 2–4 pH units, caused by the binding of the dissociated form of the reagents. The reason for these changes in the absorption spectra and protolytic properties of both reagents is the formation of hydrophobically hydrated ionic associates of azo compounds with the cetylamine cation.

Spectrofluorometric determination of copper and lead in human plasma using 6,7-dihydroxy-4-methylcoumarin: Investigating their role in chronic otitis media

Chronic otitis media is a recurrent middle ear infection that poses a common health risk globally, particularly in the developing countries. Association between heavy metals, specifically copper and lead and otitis media has been underexplored. Herein, a spectrofluorometric method was developed to determine copper and lead in human plasma samples investigating their association with chronic otitis media. The method utilizes feasible interaction of 6,7-dihydroxy-4-methylcoumarin, with copper and lead to yield different fluorescent compounds that provides measurable approaches for their levels in the plasma matrix. Copper is quantitatively analyzed based on its quenching ability for the fluorescence of 6,7-dihydroxy-4-methylcoumarin exhibiting concentration-dependent behavior. On the other hand, lead forms a fluorescent complex with 6,7-dihydroxy-4-methylcoumarin that has remarked fluorescence enhancement and bathochromic shift, enabling sensitive lead quantification. The method was briefly validated and introduced accepted linear relationship over a concentration range of 100–3000 ng/mL for copper and 200–4000 ng/mL for lead. The method was used to determine the levels of copper and lead in the human plasma samples of healthy volunteers and patients with chronic otitis media. The results revealed a decrease in copper levels and an increase in lead levels in otitis media patients compared to healthy controls. These findings suggest a potential association between copper and lead levels and chronic otitis media, warranting further investigation into their role in the condition.

Stability and photophysical study of bright day light fluorescent material and its fabrication in laser patterning and LED application

Developing aggregation-induced emission (AIE) active highly visible fluorescent dyes is of great importance because of its numerous applications. We have successfully developed and synthesized two novel napthalimide based molecules PU1 and PU2, that exhibit bright greenish yellow in day light and vivid green emission when exposed to UV light. Compounds PU1 and PU2 exhibit variable emission behavior at different solvent polarities. Upon raising the solvent polarity from ether to DMF, emission maxima of PU1 and PU2 underwent a bathochromic shift. Additionally, compounds PU1 and PU2 show signs of AIE, which cause a restriction in intramolecular mobility. A distinct self-assembled structure was generated at 30 % aqueous DMF solution following aggregation, as demonstrated by experiments using dynamic light scattering and field emission scanning electron microscopy. Compounds PU1 and PU2 have been blended with poly(urethane) to develop a polymeric film. Tensile strain studies, and TGA, DSC analyses were used to examine the thermal/mechanical stability of PU films. The photostability of PU1 and PU2 in both solution and polymeric film was examined using a 5-h UV-beam irradiation. Furthermore, in the presence of trifluoroacetic acid, the blended polymeric film and 365 nm LED light coated material exhibits distinct colorimetric and fluorimetric transformations. Finally, laser-induced periodic surface structure (LIPSS) pattern processing on PU1 coated substrates can be extended for optical applications.

Synthesis, Structural, Electrochemical, and DFT Studies of Highly Substituted Nonplanar Ni(II) Porphyrins and Their Intensity-Dependent Third-Order Nonlinear Optical Properties.

We designed and successfully synthesized highly substituted electron-deficient nonplanar Ni(II) porphyrins and their derivatives (1-7) in moderate to good yields. These derivatives were comprehensively characterized by various spectroscopic techniques and single-crystal X-ray diffraction (SCXRD) analysis. SCXRD analysis confirmed the structures of compounds 2, 4, and 7, adopting saddle-shape geometry. These nonplanar porphyrins demonstrated significant bathochromic shifts in their absorption spectra compared to parent NiTPP, attributed to the influence of bulky β-substituents and/or peripheral fusion. π-Extended porphyrins 6 and 7 displayed panchromatic absorption spectra extending into the NIR region. Porphyrins 6 and 7 demonstrated a profound anodic shift (∼400 mV) in their first reduction peak potentials compared to precursor NiTPP(NO2)Br6. The experimental absorption spectral pattern matches the simulated absorption spectra obtained from TD-DFT studies. The femtosecond laser intensity-dependent third-order nonlinear optical studies revealed that NiDFP(VCN)2Br6 (6) and NiDFP(VCN)2(PE)6 (7) displayed giant optical nonlinearities compared to the other porphyrins. Among all, NiDFP(VCN)2Br6 (6) possessed the highest two-photon absorption coefficient (β) and cross-section (σTPA) values in the range of 22-33 × 10-10 m/W and 3.77-6.95 × 106 GM, respectively. These findings suggest that the investigated nonplanar π-extended porphyrins are promising candidates for future optoelectronic applications.

Cu(β-diketonato)2 bathochromic shifts from the ultraviolet towards the visible region

ContextThe DFT-calculated ultraviolet/visible properties of 11 different Cu(β-diketonato)2 complexes are presented. The selected β-diketonato ligands on the Cu complex contain none, one or two aromatic rings. The experimentally measured absorbance maxima range of the ultraviolet/visible is observed at 295–390 nm, and the calculated range is 302–425 nm, for the 11 complexes in this study. More aromatic rings on the ligand lead to bathochromic shifts of the experimentally measured absorbance maxima from the ultraviolet towards the visible region. Absorbance maxima of the Cu(β-diketonato)2 complexes with no aromatic rings on the ligand are found to be predominantly ligand-to-metal charge transfer excitations, whereas introducing one or two aromatic rings shifts the excitations to predominantly ligand-to-ligand charge transfer.MethodsDFT calculations were conducted on the neutral molecules with multiplicity 2, using the PBEh1PBE functional and the aug-cc-pVDZ basis set as implemented in the Gaussian 16 package. The selected solvent was acetonitrile, the solvent in which most of the experimental UV/Vis are reported. The molecules were all optimized in the solvent phase, using the IEFPCM. The initial coordinates for the compounds were generated using Chemcraft.HighlightsTDDFT of 11 different Cu(β-diketonato)2 complexes follow the experimental trend.Aromatic rings on the ligand lead to Bathochromic shifts of UV/Visible spectra.No aromatic rings on the ligand lead to ligand-to-metal charge transfer excitations.Aromatic rings on the ligand lead to ligand-to-ligand charge transfer excitations.Graphical abstractBathochromic shifts in eco-friendly Cu(β-diketonato)2.

WazaGaY: An Innovative Aza-BODIPY-Derived Near-Infrared Fluorescent Probe for Enhanced Tumor Imaging.

Aza-BODIPYs represent a class of fluorophores in which the π-conjugated system is rigidified and stabilized by a boron atom. A promising strategy to enhance their fluorescence properties involves replacing the boron atom with a metal ion. Here, we describe the synthesis and characterization of a water-soluble derivative where the metal is a gallium(III) ion, termed WazaGaY (water-soluble aza-GaDIPY). Water solubility is ensured by two ammonium substituents, inducing a bathochromic shift and a significant increase in quantum yield compared to that of the dimethylamino analog. The cellular behavior of WazaGaY-1 was observed across different tumor cells. In vivo, the distribution and safety profiles were determined, and tumor uptake was assessed in various tumor types. Following intravenous injection, WazaGaY-1 enabled clear discrimination of tumors engrafted subcutaneously in mice with high tumor-to-muscle ratios (ranging from 7 to 20), even in the absence of specific conjugation. Its potential as a contrast agent for fluorescence-guided surgery was confirmed.

Synthesis, nonlinear optical activity, solvents effect, β-cyclodextrin effect, and cytotoxic activity on skin fibroblast and breast cancer cell lines of a new chalcone derivative of nabumetone

The use of small organic molecules, such as chalcones, for efficient applications as organic luminescent materials has attracted increasing attention owing to their interesting optical, photophysical, and biological properties. In this study, a new chalcone, 1-(4-isopropylphenyl)-5-(6-methoxynaphthalen-2-yl)pent-1-en-3-one (INM), was synthesized via base condensation between nabumetone and cuminaldehyde. INM was subsequently identified and characterized by FT-IR, NMR spectroscopy (1H and 13C), mass spectrometry, elemental analysis, X-ray diffraction, thermogravimetric analysis, and FESEM studies. Investigation of the solvent effect revealed that the π → π* transition involved a bathochromic shift from hexane to water and a large Stokes-shifted, twisted intramolecular charge-transfer emission in water. Diffuse reflectance spectral studies confirmed the formation of transparent INM chalcones with excellent crystallinity, and photoluminescence studies substantiated the low recombination rate of electrons and holes. Tauc plot analysis with the Kubelka–Munk algorithm revealed higher direct (3.57 eV) and indirect (3.41 eV) bandgap energies of INM. Density functional theory calculations at B3LYP/6-31G(d,p) revealed that INM had promising nonlinear optical activity (β ≈ 30.504 × 10−30 compared to a reference material, urea. Cell biocompatibility was evaluated after culturing skin fibroblasts and breast cancer cells with INM using the MTT assay and fluorescence microscopy of the live/dead cell assay. It was observed that INM exhibited good NIH/3T3 cell adhesion and proliferation and the weak inhibiting ability of MDA-MB231.

Unveiling peripheral symmetric acceptors coupling with tetrathienylbenzene core to promote electron transfer dynamics in organic photovoltaics

Non-fullerene organic compounds are promising materials for advanced photovoltaic devices. The photovoltaic and electronic properties of the derivatives (TTBR and TTB1-TTB6) were determined by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses using the M06/6-311G(d,p) functional. To enhance the effectiveness of fullerene-free organic photovoltaic cells, modifications were applied to end-capped acceptors by using strong electron-withdrawing moieties. The structural tailoring showed a significant electronic impact for HOMO and LUMO for all chromophores, resulting in decreased band gaps (3.184–2.540 eV). Interestingly, all the designed derivatives exhibited broader absorption spectra in the range of 486.365–605.895 nm in dichloromethane solvent. Among all derivatives, TTB5 was observed to be the promising candidate because of its lowest energy gap (2.54 eV) and binding energy (0.494 eV) values, along with the bathochromic shift (605.895 nm). These chromophores having an A–π–A framework might be considered promising materials for efficient organic cells.

Side-chain engineering of 4-aryl-1,8-naphthalimides: Fine-tuning for mechnochromic and vapochromic response in dual-state emission mode

An alkyl chain engineering strategy is described to design mechanochromic and vapochromic response molecules with dual state emission. Based on a red emissive AIE-active fluorophore (NAPTPA-phenol), the alkyl chains with different length (C2 ∼ C8) are introduced to construct NAPTPA1-4 via an ester linker. All four compounds display dramatic emissions in both aggregation and solid states, which showed higher quantum yields than their precursor NAPTPA-phenol. Among these compounds, NAPTPA1 with the C2 alkyl chain shows the largest bathochromic shift (∼50 nm) from 560 nm (Φ = 92.2 %) to 610 nm (Φ = 59.2 %) between two solid states. The large shift might be assigned to the efficient intramolecular charge transfer between naphthalimide and triphenylamine and two different stacking modes (self-assembly and amorphous). The high fluorescence quantum yields in aggregation state should be attributed to restricted of intramolecular rotation of the rotor-shape 4-arylnaphthalimide fluorophores. Furthermore, the needle-like self-assembly structure is seen in the SEM pattern of NAPTPA1, which exhibited large difference comparing to NAPTPA-phenol and NAPTPA2 ∼ 4. After grinding, the amorphous forms were given to all compounds that led their similar emission bands in red region centered on 610 nm. With the dramatic dual emission color, NAPTPA1 with short side chain (C2) was used to perform a vapochromic reverse courses by using the common VOCs to fume the NAPTPA1-loaded filter paper. The test exhibits the obvious color transformation and fast reversing time (<20 s) indicating the test strip can be successfully implemented to monitor VOCs.

Impressive nonlinear optical response of π-conjugated, photoluminescent soft nanoparticles in polymer matrix

Nonlinear optical (NLO) materials are useful for applications varying from modulation of optical signals to cancer therapy. Besides inorganic crystals and organic molecules with defined structures, carbonized products have emerged as a new generation of materials showing good NLO properties. Due to the small sizes, the NLO performance of such materials mainly originates from nonlinear absorption. Obtaining a product with a high content of π-conjugated moiety is the key to improving the NLO performance. By using aldehydes bearing π units as the precursors, in this work we synthesized three polymeric nanoparticles (PNPs) through one-step pyrolysis, which also have large contents of π-conjugated structures. It was found that a larger size of π unit in the precursor led to a higher content as well as the size of the π-conjugated structure, which induced a bathochromic shift in the emission and an improved performance in the NLO response. When embedded in polymethylmethacrylate films, the products showed reverse saturable absorption (RSA) behavior with β up to 4.20 × 10−6 m W−1 and optical limit threshold down to 0.0012 J cm−2, which are comparable to those of metal-doped counterparts. This work gives deep insight on the structure-property relationship of the pyrolyzed products from π-conjugated small molecules, which is also useful for the preparation of task-specific carbon dots (CDs) or PNPs in future.

Complexation of ThoriumIV with Fluorinated Heterocyclic β‐Diketones in Aqueous Hydrochloric Solutions

AbstractThe interaction of Thorium(IV) with a group of non‐symmetric CF3‐diketones has been studied by means of electronic absorption spectroscopy in HCl aqueous solutions at I=0.5 M (NaCl) and T=298 K. Six heterocyclic dicarbonyl ligands (2‐thenoyl‐trifluoroacetone, 2‐furoyl‐trifluoroacetone, 2‐selenophen‐trifluoroacetone, 2‐tellurophen‐trifluoroacetone, phenyl‐trifluoroacetone, and 2‐naphthyl‐trifluoroacetone) demonstrate the chelation activity toward ThIV in the acidic pH range. Obtained values of the “true” stability constants lie in the range 6.2–6.8 logarithmic units, respectively. A significant (10–15 nm) bathochromic shift between the maximum absorption wavelength of lanthanide and actinide monocomplexes has been detected. Observed spectral shift increases with the atomic number of substituted chalcogen atoms in the heterocyclic ring of the corresponding ligand: 10 nm for furan, 11 nm for thiophen, 14 nm for selenophen, and 15 nm for tellurophene rings. The complexation with Thorium occurs in an acidic media, where studied ligands do not interact with transition and rare earth metals. Spectral and pH shifts make studied ligands useful reagents for the detection and analytical determination of Thorium in the mixture with other metals without prior separation. Quantum‐chemical simulations (DFT and TD‐DFT) demonstrate that the nine‐ and deco‐coordinated structures of ThoriumIV complexes reproduce experimental values within reasonable errors.

Precise intramolecular-charge-transfer property modulation of D-A-type fluorescent probes for bifunctional detection of phosgene and nerve agent

Chemical warfare agents such as phosgene and nerve agents pose severe threats to national defense and public safety, yet the development of bifunctional ratiometric fluorescent probes for them is still in its infancy. Aimed at this target, an intramolecular-charge-transfer (ICT) modulation strategy via incorporating donors with varied electron-donating ability, is put forward. Based on it, a series of donor(D)-acceptor(A)-type fluorescent probes are designed and synthesized. It is found that as the ICT strength of probes weakens, a ratiometric fluorescent probe with bi-analyte identification of phosgene and diethylchlorophosphate (DCP, the mimic of nerve agent sarin) is gained. Upon exposure to phosgene and DCP, 3-(benzo[d]thiazol-2-yl)-4′-(1,2,2-triphenylvinyl)-[1,1′-biphenyl]-4-amine (BTTPE), with the weakest ICT property, presents discriminative bathochromic shifts (Δλem = 58 nm for phosgene and Δλem = 152 nm for DCP) and favorable limits of detection (LODs in solution: 6.42 nM for phosgene; 6.80 µM for DCP). Besides, the prepared BTTPE-based paper test strips combined with a smartphone can detect phosgene vapor under the colorimetric-fluorescent dual-mode sensing and enable the visual recognition and quantitative detection of DCP vapor, with LODs in the vapor phase of 0.29 ppm for phosgene and 0.49 ppm for DCP. Hereby, this work not only provides the ICT modulation strategy for the first time to realize the ratiometric fluorescence detection of phosgene/DCP but also opens up a new avenue for tailoring multifunctional fluorescent probes.

Synthesis of 2,2,3,3‐Tetraphenyl‐5,5,6,6,7,7,8,8‐octamethyl‐2,3,5,6,7,8‐hexasilabicyclo[2.2.2]octane – a Phenyl‐substituted Silicon‐containing Cage

AbstractMolecular cages that contain silicon are highly versatile and stable materials with great potential for various scientific and technological applications due to their ability to form stable three‐dimensional frameworks. The synthesis of 2,2,3,3,5,5,6,6,7,7,8,8‐dodecamethyl‐2,3,5,6,7,8‐hexasilabicyclo[2.2.2]octane has already been reported and its modifications at the CH moiety have been demonstrated to afford varied functionality. Here, we present the synthesis and characterization of 2,2,3,3‐tetraphenyl‐5,5,6,6,7,7,8,8‐octamethyl‐2,3,5,6,7,8‐hexasilabicyclo[2.2.2]octane, which is a phenyl‐substituted analogue of such a silicon‐containing cage. The Ph‐substituted Si‐containing cage exhibits a low‐lying LUMO due to the hyper‐conjugation including Si−Si, Si−C σ*‐orbitals, and π(phenyl)‐orbitals, which results in a remarkable bathochromic shift in the UV‐vis absorption spectrum.

Cm(III) speciation in the presence of citrate from neutral to hyperalkaline conditions and the effect of calcium

We investigated the binary Cm-citrate system using time-resolved laser fluorescence spectroscopy (TRLFS), parallel factor analysis (PARAFAC), and quantum chemical calculations. Evidence collectively suggests the stepwise coordination and deprotonation of citrate alcohol groups in Cm-cit complexes with two bound citrate moieties upon increasing pH, which is supported by a bathochromic shift in emission spectra, an observed increase in lifetime measurements, and lower energy minima for citrate alcohol involvement versus hydrolysis of the Cm-citrate species. Our PARAFAC results agree with a 3-component model for the Cm-citrate system and offer pure component decompositions, yielding fraction species across the studied pH range that have a correlated slope = 1 as a function of pH. For the first time, evidence of ternary Ca-Cm-citrate complexes was revealed by TRLFS with increasing calcium concentration at fixed pHm. The formation of these ternary complexes was substantiated with density functional theory (DFT) calculations on simple model systems of the complexes. Shared citrate carboxylate groups between calcium and curium were proposed for all three ternary Ca-Cm-cit complexes based on DFT-determined Ca–O and Cm–O distances. Moreover, we found that the ternary complex with both alcohol groups deprotonated is most stable when it shares both two carboxylate and two alcohol groups between Ca and Cm. The presence of shared functional groups highlights the enhanced stability of these ternary complexes. Additional work is warranted to further constrain the stoichiometry, stability constants and dependence on ionic strength of these complexes for purposes of thermodynamic modeling of repository settings.

Exploration of the effect of multiple acceptor and π–spacer moieties coupled to indolonaphthyridine core for promising organic photovoltaic properties: a first principles framework

Herein, the indolonaphthyridine-based molecules (INDTD1–INDTD8) with A1–π–A2–π–A1 configuration were designed by the end-capped modification of INDTR reference with various acceptors. The density functional theory (DFT) and time-dependent DFT (TD-DFT) analyses at M06/6-31G(d,p) level were reported in this research to explore their optoelectronic and photovoltaic features. Their geometrical structures were initially optimized at the afore-said level and followed by various calculations such as the frontier molecular orbitals (FMOs), UV–Visible, density of states (DOS), transition density matrix (TDM), binding energy (Eb), open circuit voltage (Voc) and fill factor (FF). Moreover, their global reactivity parameters (GRPs) were depicted by using the HOMO–LUMO band gaps obtained from the FMOs study. The tailored molecules demonstrated lower band gaps (2.183–2.269 eV) than INDTR (2.288 eV). They also showed bathochromic shifts in the visible region in chloroform (735.937–762.318 nm) and gas phase (710.384–729.571 nm) as compared to INDTR (724.710 and 698.498 nm, respectively). Further, intramolecular charge transfer (ICT) was demonstrated via the DOS and TDM graphical maps. Among all the entitled chromophores, INDTD7 showed significantly reduced band gap (2.183 eV), red-shifted absorption value (760.914 nm) in chloroform solvent and minimal Eb value (0.554 eV). The presence of –SO3H groups on the terminal acceptors of INDTD7 may enhance the mobility of charges. The results suggested that the newly designed chromophores can be effective candidates for the future organic solar cell applications. Moreover, this study may encourage the experimentalists to develop photovoltaic materials.

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).

Illuminating light on D-π-A Zn porphyrin dyes for efficient solar to chemical fuel generation

In this study, we design tunable D-π-A porphyrin dyes, 2,1,3-benzo thiadiazole (BTD)-phenyl (LG-6) and 4-ethynyl thiophene (LG-5) as photosensitizers of Pt/TiO2 (PCT) for solar to chemical fuel generation. The PCT-LG5 and PCT-LG6 photocatalysts are evaluated for photoinduced hydrogen evolution and CO2 reduction to methanol. The PCT-LG6 at optimum (pH 1, 3, 7, and 10) reaction conditions produced hydrogen generation rate of 5.70 mmol.g−1.h−1 with a turnover number (TON) of 1140 and apparent quantum yield (AQY) of 13.8% under visible-light and remarkably high CO2 reduction reaction to methanol with a rate of 1.99, 1.38 mmol.g−1.h−1 for PCT-LG5, PCT-LG6 systems, respectively. The extended light absorptions (400–900 nm) of the photocatalysts is due to the correct pairing of functionalization between porphyrin and the anchoring group cyanoacrylic acid in LG-5 and carboxylic acid in LG-6. The cyanoacrylic group acts as an anchoring group in LG-5, inducing a red (bathochromic) shift in the Soret band and Q-bands, indicating effective intramolecular electronic charge transfer behavior alongside the implementation of strategies to enhance light harvesting properties which further substantiated by the density functional theory (DFT) studies.

Dithieno[3,2‐b; 2′,3′‐f]phosphepinium‐Based Near‐Infrared Fluorophores: px–π* Conjugation Inherent to Seven‐Membered Phosphacycles

AbstractPositively charged phosphorus‐containing heterocycles are characteristic core skeletons for functional molecules. While various phosphonium‐containing five‐ or six‐membered‐ring compounds have been reported, the seven‐membered‐ring phosphepinium have not been fully studied yet. In this study, dithieno[3,2‐b; 2′,3′‐f]phosphepinium ions containing electron‐donating aminophenyl groups were synthesized. An X‐ray crystallographic analysis of the resulting donor–acceptor–donor dyes revealed a bent conformation of the central seven‐membered ring. These compounds exhibit fluorescence in the near‐infrared region with a bathochromic shift of ca. 70 nm compared to a phosphepine oxide congener and a large Stokes shift. High fluorescence quantum yields were obtained even in polar solvents due to the suppression of the nonradiative decay process. A theoretical study revealed that the phosphepinium skeleton is highly electron‐accepting owing to the orbital interaction between a px orbital of the phosphonium moiety and a π* orbital of the 1,3,5‐hexatriene moiety. Due to the lower‐lying px orbital in the phosphonium moiety compared to that of the phosphine oxide and the bent conformation of the seven‐membered ring, the phosphepinium ring permits effective px–π* conjugation. A large structural relaxation with a contribution of a quinoidal resonance structure is suggested in the excited state, which should be responsible for the bright emission with a large Stokes shift.