Search

We present a series of six hypervalent bismuth complexes Bi(R1PDPR2)X bearing ligands characterized by the pyridine‐2,6‐bis(pyrrolide) (PDP) structural motif. While bismuth holds considerable potential for facilitating efficient intersystem crossing (ISC), reports on phosphorescent molecular bismuth complexes are still scarce and mostly based on systems that exhibit inter‐ or intraligand charge transfer character of their optical excitations. Herein, the UV/vis absorptive, luminescent, and electrochemical properties of complexes Bi(R1PDPR2)X are explored, where the substituents R1 and R2, as well as the halide ligand X are varied. These compounds are characterized by an intense HOMO→LUMO transition of mixed ligand‐to‐metal charge transfer (LMCT) and interligand charge transfer (LL'CT) character, as shown by time‐dependent density functional theory (TD‐DFT) calculations. At 77 K in a 2‐MeTHF matrix, these compounds exhibit red, long‐lived phosphorescence with lifetimes ranging from 479 to 14 μs. Cyclic voltammetry measurements and TD‐DFT calculations show that the substituents influence HOMO and LUMO energies to almost equal extent, resulting in nearly constant emission wavelengths throughout this series. Single‐crystal X‐ray diffraction studies of four of the six complexes exemplify the inherent Lewis acidity of the coordinated Bi3+ ion, in spite of its hypervalency. [ABSTRACT FROM AUTHOR]

In this work, we synthesize a series of push–pull compounds bearing naphthalimide as the electron acceptor and tetraphenylethylene (TPE)/triphenylamine (TPA)/phenothiazine (PTZ) as the electron rich/electron donor units. These moieties are arranged in highly conjugated quadrupolar structures. The structure–property relationships are investigated through a joint experimental time–resolved spectroscopic and computational TD–DFT study. The femtosecond transient absorption and fluorescence up–conversion experiments reveal ultrafast photoinduced intramolecular charge transfer. This is likely the key factor leading to efficient spin–orbit CT–induced intersystem crossing for the TPA– and PTZ–derivatives as well as to small singlet–to–triplet energy gap. Consequently, evidence for a delayed fluorescence component is found together with the main prompt emission in the fluorescence kinetics both in solution and in thin film. The weight of the Thermally Activated Delayed Fluorescence (TADF) is greatly enhanced when these fluorophores are used as guests in solid–state host matrices. TADF is interestingly revealed in the orange–red region of the visible. Such long wavelength emission is here observed with surprisingly large fluorescence quantum yields, thanks to the conjugation enhancement achieved in these newly synthesized structures relative to previous studies. Our findings may be thus promising for the future development of efficient third generation TADF–based OLEDs. [ABSTRACT FROM AUTHOR]

Herein, we have designed aqueous dispersed self‐assembled nanostructures with diverse morphologies from the zinc tetraphenyl porphyrin (ZnTPP) monomer employing simple solution‐based coprecipitation methods. Detailed morphological studies have been carried out by various electron microscopy techniques. Finally, the structural features were correlated with the underpinning photophysical processes using steady‐state and time‐resolved spectroscopy. Detailed studies suggest that controlled morphology and highly defined intermolecular interactions affect the overall photoinduced charge transfer process. Based on the fundamental investigations, all these different types of nanostructures have been utilized as photocatalysts for solar hydrogen production without using any cocatalysts, and it was found that the spherical nanostructure exhibits significantly higher H2 production rates of ∼1682 μ mole/g, which is a few folds higher than other 1D and 2D nanostructured materials. The experimental findings were further supported by the TD‐DFT study. Furthermore, the detailed computational studies suggest that the spherical aggregates exhibited a more vital interaction between the ZnTPP molecules, causing significant electronic coupling between bright local excited and charge transfer states, which supports our experimental findings. Finally, we have selectively utilized the oxidative half‐reaction for the simultaneous transformation of glycerol to valuable chemicals along with photocatalytic H2 production through reductive half‐reaction. [ABSTRACT FROM AUTHOR]

A range of novel BODIPY derivatives with a tripodal aromatic core was synthesized and characterized spectroscopically. These new fluorophores showed promising features as probes for in vitro assays in live cells and offer strategic routes for further functionalization towards hybrid nanomaterials. Incorporation of biotin tags facilitated proof‐of‐concept access to targeted bioconjugates as molecular probes. Computational explorations using DFT and TD‐DFT calculations identified the most stable tripodal linker conformations and predicted their absorption and emission behavior. The uptake and speciation of these molecules in living prostate cancer cells was imaged by single‐ and two‐photon excitation techniques coupled with two‐photon fluorescence lifetime imaging (2P FLIM). [ABSTRACT FROM AUTHOR]

In(III) tetraarylporphyrin complexes with 4‐thiomethylphenyl (1‐InPor), thien‐3‐yl (2‐InPor), thien‐2‐yl (3‐InPor) and 5‐bromothien‐2‐yl (4‐InPor) meso‐aryl rings have been synthesized and characterized. The complexes have been conjugated to gold and silver nanoparticles (AuNPs and AgNPs). The photodynamic antimicrobial chemotherapy (PACT) activities of 1–4‐InPor and their AuNP and AgNP conjugates have been investigated against both planktonic bacteria and biofilms of Gram‐(+) S. aureus and Gram‐(−) E. coli. 2.5 μg.mL−1 solutions of 1–4‐InPor exhibited favorable PACT activities against planktonic S. aureus with high Log10 reduction values in the 4.28–7.69 range upon 75 min photoirradiation with a Thorlabs M625L3 LED (240 mW.cm−2) mounted onto the illumination chamber of a Modulight 7710 medical laser system to provide a dose at the well‐plate of 86 mJ.cm−2.min−1. In contrast, low values in the 1.4–1.9 range were obtained against E. coli with 10 μg.mL−1 solutions. 1–4‐InPor exhibited relatively low PACT activity against the biofilm cells of S. aureus and E. coli. Conjugation of 1–4‐InPor to AgNPs and AuNPs significantly enhanced the PACT activities. This is demonstrated by the complete eradication of planktonic S. aureus at shorter irradiation times with high Log10 values>7.69 and moderate Log10 values>2 against planktonic E. coli for the meso‐thienylporphyrin conjugates. [ABSTRACT FROM AUTHOR]

Novel benzidine bis azo (BBA) complexes with Fe(III), Co(III), Ni(II), Cu(II), and Zn(II) were created and analyzed using a variety of analytical methods. The B3LYP/6-311G(d,p) and LANL2DZ basis sets were used in quantum chemical simulations with the DFT approach to analyze the structures of the BBA and its complexes. The compounds' strong NLO properties can be easily polarized, as indicated by the narrow HOMO-LUMO energy gap. The polarizability and hyperpolarizabilities of the chelates indicate that they are good candidates for NLO materials. The electronic spectra were computed using the polarizable continuous solvation method PCM, TD-DFT/PCM. Additionally, the infrared spectra obtained were compared to the anticipated harmonic vibrations of the azo dye ligand and its complexes. Utilizing molecular docking and virtual screening technologies, binding energy studies of the bis azo dye ligand and its complexes with the human coronavirus Nl63 nucleocapsid protein (PDB ID: 5epw) and SARS-CoV spike protein (PDB ID: 5wrg) were anticipated. The results demonstrated promising binding. The outcomes demonstrated the efficiency of the ligand and its complexes as COVID-19 and SARS virus inhibitors. Zn was shown to be the only metal that connected to the 5epw-Viral protein. [ABSTRACT FROM AUTHOR]

Within this work we have investigated spiro‐based tetrathiafulvalenes (TTFs) obtained as mixtures of stereoisomers from racemic spiro[5.5]undeca‐1,8‐dien‐3‐one. Compared to previously described spiro‐TTFs, enantiomeric and diastereoisomeric forms have been here separated by chiral HPLC and fully characterized both experimentally and theoretically. The two types of spiro‐based chiral derivatives contain either one (2) or three (1) chiral centres out of each one is spiro‐type. Experimental CD, supported by TD‐DFT calculations, shows differences in the optical activity between the 1 and 2 and their intermediates. The low optical activity of 2 and 3 (spiro alone chirality) was attributed to the presence of two conformers in the solution (ax and eq) of opposite Cotton effect whereas in the case of 1 and 5 (spiro and stereogenic centres) the spiro chirality seems to be responsible of the Cotton effect in the high energy region whereas the R and S chirality in the low energy region. Racemic and enantiopure forms have been successfully used for the synthesis of charge transfer complexes with tetracyanoquinodimethane (TCNQ) based acceptors. [ABSTRACT FROM AUTHOR]

A novel centrosymmetric hybrid organic-inorganic material (1,4-dimethylpiperazine tetrachlorocuprate (II)) has been prepared and analyzed using single crystal X-ray diffraction, spectroscopic studies, photoluminescence properties, DFT studies and Hirshfeld surface analyses. The single crystal X-ray analysis indicates that the compound crystallizes in the P21/c monoclinic space group. The N–H···Cl hydrogen bonds are alternately connected by organic cations [C6H16N2]2+ and inorganic moieties [CuCl4]2-. The Hirshfeld surfaces investigated the nature and quantity of different interactions and their role in crystal packing. Infrared and Hirshfeld measurements were performed to confirm the results obtained by X-ray diffraction. In addition, optical measurements were used to investigate the IR and photoluminescence properties. The di-electrical investigations show interesting electrical behavior of the compound. In addition, an insilico investigation using molecular docking of the compound against SARS-CoV-2 variation (B.1.1.529) was also conducted to better understand the non-covalent interaction of cuprate(II) complexes with active amino acids in the SARS-CoV-2 spike proteins. These studies were supported by drug-likeness and absorption, distribution, metabolism, and excretion (ADME) analyses. [ABSTRACT FROM AUTHOR]

Organic photovoltaic cells are electronic devices that convert sunlight into electricity. To this end, the number of studies on organic photovoltaic cells (OVCs) is growing, and this trend is expected to continue. Computational studies are still needed to verify and prove the capability of CVOs, specifically the nanometer molecule PCBM, based on successful experimental results. In this paper, we present a theoretical and computational investigation of PCBM and PC71BM derivatives using the DFT method. On this basis, we employ independent and time-dependent density theories. HOMO, LUMO and GAPH-L energies, ionization potentials and electronic affinity are determined and found to be in agreement with experiments. Using DFT theory based on B3LYP and M062X methods with bases 6-31G (d,p) and 6-311G (d), calculations show that the most efficient acceptors are presented in the group of PC71BM derivatives and are in substantial agreement with experiments. The geometries of the structures are optimized by Gaussian 09. [ABSTRACT FROM AUTHOR]

Nanosecond time‐resolved X‐ray (tr‐XAS) and optical transient absorption spectroscopy (OTA) are applied to study 3 multimolecular photocatalytic systems with [Ru(bpy)3]2+photoabsorber, ascorbic acid electron donor and Co catalysts with methylene (1), hydroxomethylene (2) and methyl (3) amine substituents in pure water. OTA and tr‐XAS of 1 and 2 show that the favored catalytic pathway involves reductive quenching of the excited photosensitizer and electron transfer to the catalyst to form a CoII square pyramidal intermediate with a bonded aqua molecule followed by a CoI square planar derivative that decays within ≈8 μs. By contrast, a CoI square pyramidal intermediate with a longer decay lifetime of ≈35 μs is formed from an analogous CoII geometry for 3 in H2O. These results highlight the protonation of CoI to form the elusive hydride species to be the rate limiting step and show that the catalytic rate can be enhanced through hydrogen containing pendant amines that act as H−H bond formation proton relays. [ABSTRACT FROM AUTHOR]

The design and synthesis of a new fluorophore containing an arylidene thiazole scaffold resulted in a compound with good photophysical characteristics. Furthermore, the thiazole C5‐methyl group was easily modified into specific functional groups (CH2Br and CH2OH) for the formation of a series of photocourier molecules containing model compounds (benzoic acids), as well as prodrugs, including salicylic acid, caffeic acid, and chlorambucil via a "benzyl" linker. Spectral characteristics (1H, 13C NMR, and high‐resolution mass spectra) corresponded to the proposed structures. The photocourier molecules demonstrated absorption with high values of coefficient of molar extinction, exhibited contrasting green emission, and showed good dark stability. The mechanism of the photorelease was investigated through spectral analysis, HPLC‐HRMS, and supported by TD‐DFT calculations. The photoheterolysis and elimination of carboxylic acids were proved to occur in the excited state, yielding a carbocation as an intermediate moiety. The fluorophore structure provided stability to the carbocation through the delocalization of the positive charge via resonance structures. Viability assessment of Vero cells using the MTT‐test confirmed the weak cytotoxicity of prodrugs without irradiation and it increase upon UV‐light. [ABSTRACT FROM AUTHOR]

Luminescent diimine-Pt(IV) complexes [Pt(N^N)(Me)2(PhSe)2], (N^N = 2,2′-bipyridine (bpy, 1b), 1,10-phenanthroline (phen, 2b), and 4,4′-dimethyl-2,2′-bipyridine (Me2bpy, 3b), PhSe− = phenyl selenide were prepared and identified using multinuclear (1H, 13C{1H} and 77Se{1H}) NMR spectroscopy. The PhSe− ligands were introduced through oxidative addition of diphenyl diselenide to the non-luminescent Pt(II) precursors [Pt(N^N)(Me)2], N^N = (bpy, 1a), (phen, 2a), (Me2bpy, 3a), to give the luminescent Pt(IV) complexes 1b–3b. The UV-vis absorption spectra of 1b–3b are characterised by intense bands in the range 240–330 nm. We assigned them to transitions of essentially π−π* character with small metal and PhSe− ligand contributions with the help of TD-DFT (time-dependent density functional theory) calculations. The weak long-wavelength bands in the range 350–475 nm are of mixed ligand-to-metal charge transfer (L'MCT) (n(Se)→d(Pt)/intra-ligand charge transfer (IL'CT) (n(Se)→π*(Ph) or π(Ph)→π*(Ph))/ligand-to-ligand' charge transfer (LL'CT) (L = N^N, L' = PhSe−, M = Pt and n = lone pair) character. The Pt(IV) complexes showed broad emission bands in the solid state at 298 and 77 K, peaking at 560–595 nm with a blue shift upon cooling. Structured emission bands were obtained in the range 450–600 nm, with the maxima depending on the N^N ligands and the solvent polarity (CH2Cl2 vs. dimethyl sulfoxide (DMSO) and aqueous tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl) buffer). The emissions originate from essentially ligand-centred triplet states (3LC) with mixed IL'CT/L'MCT contributions as concluded from the DFT calculation. Such dominating PhSe contributions to the emissive states are unprecedented in the world of luminescent diimine-Pt(IV) complexes. [ABSTRACT FROM AUTHOR]

A Sn(IV) meso-tetra(4-methylthiolphenyl) N-confused porphyrin (4-Sn) complex was prepared to facilitate a comparison of the photophysicochemical and singlet oxygen photosensitiser properties of a series of Sn(IV) complexes of meso-4-methylthiolphenyl-substituted porphyrin, corrole, chlorin, and N-confused porphyrin. 4-Sn has an unusually high singlet oxygen quantum (ΦΔ) yield of 0.88, markedly higher than the ΦΔ values of the other complexes in this series. A Thorlabs M660L4 LED (280 mW · cm−2) was used to study the photodynamic activity of Sn-4 against the MCF-7 cancer cell line through irradiation at 660 nm for 30 min. The IC50 value was calculated to be 1.4 (± 0.8) µM, markedly lower than the previously reported values for the rest of the series. Photodynamic antimicrobial activity was also determined against Staphylococcus aureus and Escherichia coli, and 4-Sn was found to deactivate both Gram-(+) and Gram-(−) bacteria despite the absence of cationic charges on the ligand structure.

This study turns the design and screen of new compounds into a computer integer crunch of the control arrays using a scaffold based Turing machine model. If small organic fragments are stored in a fragment database (FDB) in which each fragment is labelled by an integer in an array, the position and frequency of the integer control how the fragment clicks on a scaffold (template compound). This method can robustly screen a large number of candidate fragments for solar cells and other applications such as drug design with minimal human assistance. As a proof of concept, we consider terminal imide substituents on the core perylene diimide (PDI) to develop PDI derivatives capable of absorbing UV–vis light for solar cell applications. Time dependent-density functional theory (TD-DFT) method was employed in the calculations. When the imide substituents are electron donors such as azobenzene (DPI-7), they produce a larger bathochromic shift (Δλmax) from the core DPI band position. The UV–vis absorption transitions of these DPI derivatives have more charge transfer (CT) character, as the highest occupied molecular orbitals (HOMO) are located on the fragments rather than the core DPI region. Our study presents a robust and efficient high-performance organic dye screen design strategy, and further research in DPI-based solar cell design will focus on promoting the HOMO to LUMO transitions of the optical spectra.

Several copper complexes exhibiting luminescent properties have been studied. In this context, the possibility of incorporating them into the architecture of organic light-emitting diode (OLED) devices has been investigated to improve their efficiency and photophysical stability for predicting the suitability and character of the emissive material. Specifically, we unraveled the excitation mechanism of the Cu(I)X(dppt)(PPh3) complex [X = Br, I, dppt = 3,4-bis(diphenylphosphino)thiophene]. Since the intersystem crossing (ISC) depicts a necessary process, where the knowledge of the rate constant value enables the assessment of the suitability of the material, we calculated the reverse and intersystem crossing rates for the Cu(I) complexes contrasting with pure organic thermally activated delayed fluorescence (TADF) emitters, with the goal to emphasize that the structural design of the mononuclear copper(I) complexes results in similar singlet–triplet gaps, ΔEST, values (∼0.1 eV). Moreover, it shows a remarkable enhancement of spin–orbit coupling, which allows achieving ISC rates in the ns scale. The calculations were made in the Time-Dependent Density Functional Theory (TD-DFT) level framework with the accurate response of large molecules studied here.

A Sn(IV) meso-tetra(4-methylthiolphenyl) N-confused porphyrin (4-Sn) complex was prepared to facilitate a comparison of the photophysicochemical and singlet oxygen photosensitiser properties of a series of Sn(IV) complexes of meso-4-methylthiolphenyl-substituted porphyrin, corrole, chlorin, and N-confused porphyrin. 4-Sn has an unusually high singlet oxygen quantum (ΦΔ) yield of 0.88, markedly higher than the ΦΔ values of the other complexes in this series. A Thorlabs M660L4 LED (280 mW · cm−2) was used to study the photodynamic activity of Sn-4 against the MCF-7 cancer cell line through irradiation at 660 nm for 30 min. The IC50 value was calculated to be 1.4 (± 0.8) µM, markedly lower than the previously reported values for the rest of the series. Photodynamic antimicrobial activity was also determined against Staphylococcus aureus and Escherichia coli, and 4-Sn was found to deactivate both Gram-(+) and Gram-(−) bacteria despite the absence of cationic charges on the ligand structure. [ABSTRACT FROM AUTHOR]

A novel synthesis of bis(thiazoles) and bis(thiadiazole), each connected to a thienothiophene moiety, is described. The DFT calculations support the favored synthesis of one of the anticipated bis(thiazole) regioisomers. The B3LYP/6-311G** level of theory was used to optimize quantum mechanical calculations of geometrical characteristics and energy of new compounds under study. The electronic absorption of the new compounds in ethanol solvent was handled and finished using time-dependent-density functional theory (TD-DFT) at the B3LYP/6-31G(d,p) level with the addition of the polarizable continuum solvation technique TD-DFT/PCM. The permissible singlet transitions are identified, and their involvements in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are described. Natural bond orbital (NBO) analysis was used to investigate hyper conjugative partnerships, molecular stability, and bond strength. Mean polarizability, total static dipole moment, anisotropy of polarizability, and mean first-order hyperpolarizability have all been computed. The results reveal that the compounds are promising contenders for non-linear optical materials. The molecular docking mechanism between ligands 8a–8c and COVID-19/5epw or SARS/5wrg receptors was done to explore the binding modes of these compounds at the active sites. Molecular docking results have shown that the compounds 8a–8c can be considered as a potential agent against COVID-19/5epw and SARS/5wrg receptors. [ABSTRACT FROM AUTHOR]

A new thiosemicarbazide-naphthalene-based fluorescent chemosensor FNC ((2-(furan-2-carbonyl)-N-(naphthalen-1-yl)hydrazine-1-carbothioamide)) for Zn2+ was synthesized and identified. FNC was applied to selectively detect Zn2+ with fluorescent turn-on response. The detection limit was determined to be 1.93 µM, which is much below the WHO standard (76.5 µM). The detecting mechanism of FNC to Zn2+ was revealed to bind FNC to Zn2+ in the proportion of 1: 1 by Job plot, ESI-mass and 1H NMR titrations. DFT and TD-DFT calculations were performed for FNC and FNC-Zn2+, which provide insight into structural, electronic and photophysical properties. [ABSTRACT FROM AUTHOR]

Atorvastatins play an important role in the inhibition of HMG-CoA reductase, an enzyme present in the liver that takes part in the biosynthesis of cholesterol. In this article, we report the total synthesis of a lactone–atorvastatin prodrug with additional atropisomeric features. Conformational and experimental studies of model compounds were designed to test the stability of the chiral axis. Docking calculations were performed to evaluate the constant inhibition of a library of atorvastatins. Full synthesis of the best candidate was achieved and thermally stable atropisomeric lactone–atorvastatin was obtained. The absolute configuration of the chiral axis of the atropisomers was assigned by means of chiroptical ECD spectroscopy coupled with TD-DFT calculations. [ABSTRACT FROM AUTHOR]

• Novel carbazole and diketopyrrolopyrrole-based molecule (CAR-TzDPP) was synthesized. • A comparative study between the carbazole and triazatruxene endcaps was conducted. • Experimental and theoretical properties (DFT and TD-DFT) were found in good agreement. • Two-dimensional (2D) ambipolar charge transport was observed in CAR-TzDPP thin film. • Triazatruxene-based molecule (TAT-TzDPP) provides 3D unipolar charge transport. In this work, we describe the design and synthesis of a novel soluble conjugated molecule, CAR-TzDPP , consisting of a central diketopyrrolopyrrole core (DPP) connected to carbazole endcaps through thiazole rings. To evaluate its properties, a triazatruxene-based molecule (TAT-TzDPP) was used as a model for comparison. The electrochemical and the in-solution optical properties are in good agreement with those obtained from DFT calculations. However, the thin-film self-assemblies of CAR-TzDPP exhibited distinct differences, forming a more standard crystalline structure including insulating side-chains layers that disallowed side interactions between aromatic rings. This resulted in a reduced charge transport ability to a two-dimensional (2D) ambipolar charge transport in CAR-TzDPP , compared to the nearly isotropic unipolar charge transport in TAT-TzDPP. Despite this, CAR-TzDPP can be considered a viable alternative for device configurations requiring semiconducting pathways aligned in the substrate plane due to its simplified and high yield synthesis route, ease of processing, and reliable charge mobility in OFETs. This research highlights the significance of molecular units in small semiconducting organic molecules, not only in terms of their individual optoelectronic properties but also in terms of their self-assembly capabilities, which ultimately influence their charge transport properties. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • 1,4-bis(4-vinylpyridyl)benzene (bvpb), a double heterostilbene, was synthesized and characterized. • Electrochemical Surface-Enhanced Raman Spectra (SERS) of bvpb put in evidence a resonance process at −1.0 V with 785 nm excitation line. • The study of dynamic relaxation processes by femtosecond Transient Absorption Spectra (TAS) shows a first excited state (S 1) at 607 nm in which a trans–cis rotation of the vinyl bond is involved. • DFT potential energy curve of vinyl torsion predicts a low barrier height between trans- and cis -conformers in S 1 state with a S 1 /S 0 conical intersection corresponding to a twisted vinylpyridyl bond. • The synergy of experimental data, SERS and TAS, and DFT calculations shows bvpb can act as a conformational molecular switch addressed by electric potential under a selected wavelength. The electrochemical surface-enhanced Raman spectra (SERS) of 1,4-bis(4-vinylpyridyl)benzene (bvpb) recorded at different electrode potentials with three excitation wavelengths (785, 532 and 473 nm) point out there exists a resonance process involved at more negative voltage with the 785 nm line, giving two strongly enhanced SERS bands at about 1500 and 1150 cm−1. This result agrees with the VIS-NIR transient absorption spectrum characterized by a strong band at 607 nm and a weaker one at 1163 nm, corresponding to the first singlet (S 1) and triplet (T 1) excited electronic states. The DFT potential energy curve corresponding to the trans – cis (E-Z) isomerization in the S 0 state and in the two lowest S 1 and T 1 excited states, indicates that the S 1 state exhibits a significant lower barrier height than S 0 state, showing also a S 1 /S 0 conical intersection at a structural conformation in which the vinyl double bond twists by 90°. TD-DFT resonance Raman spectra of the planar and twisted conformation in a simple model of surface complex, Ag 2 0-bvpb, yield that the twisted molecule is able to predict the selected enhancement of the two SERS bands. Therefore, bvpb could act as an electroactive conformational molecular switch under a selected wavelength in nanoelectronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • MCD and MCPL: the role of A, B and C terms. • Calculation of A and B terms via TD-DFT methods. • Porphyrinoid systems: highly symmetric and non-symmetric cases. • MCD of natural products extracted from plants: experiments and calculations. • MCD in the IR range: MVCD. A historical sketch of the MCD (magnetic circular dichroism) spectroscopy is reported in its experimental and theoretical aspects. MCPL (magnetic circularly polarized luminescence) is also considered. The main studies are presented encompassing porphyrinoid systems, aggregates and materials, as well as simple organic molecules useful for the advancement of the interpretation. The MCD of chiral systems is discussed with special attention to new studies of natural products with potential pharmaceutical valence, including Amaryllidaceae alkaloids and related isocarbostyrils. Finally, the vibrational form of MCD, called MVCD, which is recorded in the IR part of the spectrum is also discussed. A final brief note on perspectives is given. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of the structural, electronic and optical properties of few layer graphene/TiO 2 composites involving either single or bilayer graphene and the (101) surface of TiO 2 anatase, in view of the importance of carbonaceous materials such as graphene to enhance solar light-driven photocatalytic activity of TiO 2. Calculations have been performed by combining periodic DFT calculations to TD-DFT carried out on finite clusters extracted from the periodic structures and embedded in an array of point charges devised to reproduce the periodic electrostatic environment. Although van der Waals interactions dominate the graphene/TiO 2 interaction, TiO 2 properties are significantly affected by its combination with graphene in the composite materials. In particular, we found that such materials present favorable key features for photocatalysis applications, with high charge carriers mobilities, an increase of the absorption in the visible range together with a red-shift of the photoresponse of TiO 2. These results confirm that graphene can enhance solar light-driven photocatalytic activity of TiO 2 , especially when few layer graphene-based composites are considered. Furthermore, the proposed computational approach appears as a reliable and effective tool to model both the electronic and the optical properties of heterostructures at low computational cost. [Display omitted] • A reliable and effective computational protocol is proposed to model composites. • Gr-based composites offer better properties than TiO 2 for photocatalysis. • Few layer Gr-based composites offer better properties than single layer ones. [ABSTRACT FROM AUTHOR]

Wavelength‐independent conversion of organic photoswitches in the photostationary state is a rare phenomenon that opens up a way for many practical applications. In this work, three fused bis(hemi‐indigo) derivatives with different substitution patterns were synthesized and their photoswitching was investigated by optical spectroscopy, real‐time NMR spectroscopy and TD‐DFT calculations. We disclosed that the Z‐E photoisomerization of the meta‐bis(hemi‐indigo) derivative was remarkably independent of the irradiation wavelength from UV up to yellow light. The wavelength‐independent forward photoswitching together with the inhibited backward photoisomerization, high thermal stability of the photoinduced isomers as well as significant overlap between the photoswitch absorption and the solar spectrum allows to suggest bis(hemi‐indigo) derivatives as promising candidates for molecular solar thermal energy storage (MOST) systems. [ABSTRACT FROM AUTHOR]

The photoluminescence of Au(I) complexes is generally characterized by long radiative lifetimes owing to the large spin-orbital coupling constant of the Au(I) ion. Herein, we report three brightly emissive Au(I) coordination compounds, 1, 2a, and 2b, that reveal unexpectedly short emission lifetimes of 10–20 ns. Polymorphs 2a and 2b exclusively exhibit fluorescence, which is quite rare for Au(I) compounds, while compound 1 reveals fluorescence as the major radiative pathway, and a minor contribution of a microsecond-scale component. The fluorescent behaviour for 1–2 is rationalized by means of quantum chemical (TD)-DFT calculations, which reveal the following: (1) S0–S1 and S0–T1 transitions mainly exhibit an intraligand nature. (2) The calculated spin-orbital coupling (SOC) between the states is small, which is a consequence of overall small metal contribution to the frontier orbitals. (3) The T1 state features much lower energy than the S1 state (by ca. 7000 cm−1), which hinders the SOC between the states. Thus, the S1 state decays in the form of fluorescence, rather than couples with T1. In the specific case of complex 1, the potential energy surfaces for the S1 and T2 states intersect, while the vibrationally resolved S1–S0 and T2–S0 calculated radiative transitions show substantial overlap. Thus, the microsecond-scale component for complex 1 can stem from the coupling between the S1 and T2 states. [ABSTRACT FROM AUTHOR]

Multifunctional stimuli-responsive fluorophores showing bright environment-sensitive emissions have fueled intense research due to their innovative applications in the fields of biotechnologies, optoelectronics, and materials. A strong structural diversity is observed among molecular materials, which has been enriched over the years with a growing responsiveness to stimuli. Boron dipyrromethene (BODIPY) dyes have long been the flagship of emissive boron complexes due to their outstanding properties until a decade ago when analogues based on N^O, N^N, or N^C π-conjugated chelates emerged. The finality of developing borate dyes was to compensate for BODIPYs’ lack of solid-state fluorescence and small Stokes shifts while keeping their excellent optical properties in solution. Among them, the borate complexes based on a salicylaldimine ligand, called by the acronym boranils appear as the most promising, owing to their facile synthesis and dual-state emission properties. Boranil dyes have proven to be good alternatives to BODIPY dyes and have been applied in applications such as bioimaging, bioconjugation, and detection of biosubstrates. Meanwhile, ab initio calculations have rationalized experimental results and provided insightful feedback for future designs. This review article aims at providing a concise yet representative overview of the chemistry around the boranil core with the subsequent applications.

Luminescent diimine-Pt(IV) complexes [Pt(N^N)(Me)2(PhSe)2], (N^N = 2,2′-bipyridine (bpy, 1b), 1,10-phenanthroline (phen, 2b), and 4,4′-dimethyl-2,2′-bipyridine (Me2bpy, 3b), PhSe− = phenyl selenide were prepared and identified using multinuclear (1H, 13C{1H} and 77Se{1H}) NMR spectroscopy. The PhSe− ligands were introduced through oxidative addition of diphenyl diselenide to the non-luminescent Pt(II) precursors [Pt(N^N)(Me)2], N^N = (bpy, 1a), (phen, 2a), (Me2bpy, 3a), to give the luminescent Pt(IV) complexes 1b–3b. The UV-vis absorption spectra of 1b–3b are characterised by intense bands in the range 240–330 nm. We assigned them to transitions of essentially π−π* character with small metal and PhSe− ligand contributions with the help of TD-DFT (time-dependent density functional theory) calculations. The weak long-wavelength bands in the range 350–475 nm are of mixed ligand-to-metal charge transfer (L’MCT) (n(Se)→d(Pt)/intra-ligand charge transfer (IL’CT) (n(Se)→π*(Ph) or π(Ph)→π*(Ph))/ligand-to-ligand’ charge transfer (LL’CT) (L = N^N, L’ = PhSe−, M = Pt and n = lone pair) character. The Pt(IV) complexes showed broad emission bands in the solid state at 298 and 77 K, peaking at 560–595 nm with a blue shift upon cooling. Structured emission bands were obtained in the range 450–600 nm, with the maxima depending on the N^N ligands and the solvent polarity (CH2Cl2 vs. dimethyl sulfoxide (DMSO) and aqueous tris(hydroxymethyl)aminomethane hydrochloride (tris-HCl) buffer). The emissions originate from essentially ligand-centred triplet states (3LC) with mixed IL’CT/L’MCT contributions as concluded from the DFT calculation. Such dominating PhSe contributions to the emissive states are unprecedented in the world of luminescent diimine-Pt(IV) complexes.

The first example of polymer materials containing in the side chain original D‐π‐A chromophore with quinoxaline core in the π‐electron bridge is presented and their quadratic nonlinear optical (NLO) activity is studied. Two synthetic procedures: esterification and radical copolymerization, are used to obtain methacrylic copolymers P1Ch and P2Ch, respectively, which contain chromophores with quinoxaline moiety in various concentrations (4, 6, 7, and 9 mol%). Atomistic modeling has shown that introduction of chromophores in polymer side chains results in less pronounced chromophore aggregation in the material compared with the case of relative composites. NLO coefficients of the thin films obtained on the basis of copolymers P1Ch and P2Ch and composite material PMMA/AEEA‐VQV‐TCF with relative chromophore‐guest are up to 40, 21, and 43 pm/V, respectively, at chromophore content 25 wt%. Covalent attachment of chromophore moiety to the polymer side chain is shown to improve the temporal and thermal stability of the material NLO coefficient compared with that of the composite material. [ABSTRACT FROM AUTHOR]

This study investigates the optoelectronic and photoluminescence properties of graphene quantum dots (GQDs) conjugated with the Mitoxantrone (MTX) drug, aiming to enhance cancer drug delivery systems. Using DFT and TDDFT numerical simulations, we examined the impact of GQD size and MTX coupling positions (C–C, C–O, and C–N bonds) on the physical behaviour of DSGQDs. Our study confirm that all structures are energetically stable, as evidenced by the absence of negative frequencies in the IR spectra. Besides, C–O conjugated structures are found to be the most chemically stable as it was shown by global reactivity indices results. Functionalization leads to a reduced H–L energy gap, depending on the MTX coupling position and GQD size. Importantly, the optical properties of GQDs remain largely unaffected by conjugation, maintaining their stability as drug carriers. Larger GQD systems retained stable absorption and photoluminescence characteristics within the near-infrared (NIR) range, while smaller systems exhibited a shift from the visible to the NIR range. Notably, the C 48 H 18 + MTX system with C–O bonding demonstrated superior photoluminescence performance confirmed by the small line width results. These results suggest that GQDs conjugated with MTX hold significant potential for targeted cancer therapy, with minimal interaction between the drug and the GQD host, thereby reducing toxicity risks. [ABSTRACT FROM AUTHOR]

Porphyrin derivatives are known singlet oxygen sensitizers in photodynamic therapy (PDT). Energy transfer from a class of diolefinic laser dyes (DOLDs) as energy donors to the sodium salt of meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) as the accepter of energy would extend the range of photon harvesting down to the UV-region. Energy transfer was substantially enhanced in the presence of metallic silver nanoparticles (AgNPs), as revealed by steady-state emission spectroscopy, lifetimes, and quantum mechanics. DOLDs under investigation are 2,5-distyrylpyrazine (DSP), 1,4-bis (β-pyridyl-2 vinyl) benzene (P2VB), and 1,4 bis (2-methylstyryl) benzene (MSB) as efficient donors of intense absorption in the UV-region. AgNPs enhance the rate of energy transfer from DOLDs to TPPS via bringing donor and acceptor into close- proximity with a concomitant increase in dipole–dipole interaction between excited state donor and ground-state acceptor. The DOLDs molecular structures were optimized using the DFT/CAM-B3LYP/6-311G++ (d, p) level of theory. The calculated electronic absorption spectra for the studied DOLDs in the gaseous phase and methanol solvent were studied using the time-dependent density functional theory (TD-DFT) at M06-2X/6-311G++ (2d,2p) level. The calculated absorption/emission spectra for DSP laser dye in methanol are obtained at the TD/ M06-2X/6-311G++(2d, 2p) method. Notably, all theoretical results of the molecular structures under study highly agreed with the practical optical results. Energy transfer rate constants (kET) amid energy donor/acceptor pairs were determined by Stern-Volmer constants (KSV) and donors' lifetime measurements. The KSV values indicate an enhanced Fluorescence Resonance Energy Transfer (FRET) efficiencies in the presence of negatively charged AgNPs. The critical transfer distances Ro were determined from the spectral overlap between the emission spectrum of donor and absorption spectrum of TTPS. These outcomes propose the application of designed metal-enhanced FRET for energy-transfer-based assays and photodynamic therapy (PDT) applications.

We report synthesis, crystal structure, and photophysical properties of novel 1,3-phosphinoamines based on 4-amino-2,1,3-benzothiadiazole (NH2-btd): Ph2PCH(Ph)NH-btd (1) and Ph2P(E)CH(Ph)NH-btd, (E = O (2α and 2β·thf), S (3), Se (4)). Chalcogenides 2–4 exhibit bright emissions with a major band at 519–536 nm and a minor band at 840 nm. According to TD-DFT calculations, the first band is attributed to fluorescence, while the second band corresponds to phosphorescence. In the solid state, room temperature quantum yield reaches 93% in the case of the sulphide. The compounds under study feature effects of the molecular environment on the luminescent properties, which manifest themselves in fluorosolvatochromism as well as in a luminescent response to changes in crystal packing and in contributions to aggregation effects. Specifically, transformation of solid 2β·thf to solvate-free 2β either by aging or by grinding causes crystal packing changes, and, as a result, a hypsochromic shift of the emission band. Polystyrene films doped with 2 reveal a bathochromic shift upon increasing the mass fraction from 0.2 to 3.3%, which is caused by molecular aggregation effects. [ABSTRACT FROM AUTHOR]

The fast relaxation processes in the excited electronic states of functionalized aza‐boron‐dipyrromethene (aza‐BODIPY) derivatives (1–4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two‐photon absorption (2PA) and excited‐state absorption (ESA) cross‐sections were obtained for 1–4 in dichloromethane using femtosecond Z‐scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum‐chemical TD‐DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross‐sections ∼2000 GM), and large ESA cross‐sections ∼10−20 m2 of these new aza‐BODIPY derivatives 1–4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular. [ABSTRACT FROM AUTHOR]

The application of the exciton chirality method (ECM) to interpret electronic circular dichroism (ECD) spectra is a well‐established and still popular approach to assign the absolute configuration (AC) of natural products, chiral organic compounds, and organometallic species. The method applies to compounds containing at least two chromophores with electric dipole allowed transitions (e.g., π–π* transitions). The exciton chirality rule correlates the sign of an exciton couplet (two ECD bands with opposite sign and similar intensity) with the overall molecular stereochemistry, including the AC. A correct application of the ECM requires three main prerequisites: (a) the knowledge of the molecular conformation, (b) the knowledge of the directions of the electric transition moments (TDMs), and (c) the assumption that the exciton coupling mechanism must be the major source of the observed ECD signals. All these prerequisites can be easily verified by means of quantum‐mechanical (QM) calculations. In the present review, we shortly introduce the general principles that underpin the use of the ECM for configurational assignments and survey its applications, both classic ones and some reported in the recent literature. Based on these examples, we will stress the advantages of the ECM but also the key requisites for its correct application. Additionally, we will discuss the dependence of the couplet sign on geometrical parameters (angles α,β,γ between TDMs), which can be helpful for discerning the sign of exciton chirality in ambiguous situations. Finally, we will present a molecular orbital (MO) description of the exciton coupling phenomenon. [ABSTRACT FROM AUTHOR]

A set of donor‐acceptor (D‐A) substituted phenothiazine based chromophores (D‐π‐D‐π‐A, D′‐π‐D‐π‐A, D‐A′‐D‐π‐A and D′‐A′‐D‐π‐A) were designed and synthesized. The phenothiazine was substituted with the 4‐ethynyl‐1,8‐naphthalimide (NPI) on one side and a variety of donors (phenothiazine, carbazole, ferrocene and triphenylamine) were introduced on the other side of phenothiazine via Pd‐catalyzed Sonogashira cross‐coupling reaction resulting PTZ8–11. In order to tune the optoelectronic properties of the phenothiazine chromophores, cyano‐based acceptor 1,1,4,4‐tetracyanobuta‐1,3‐diene (TCBD) was incorporated by [2+2] cycloaddition‐electrocyclic ring‐opening reaction of phenothiazine derivatives PTZs 8–11 and tetracyanoethylene (TCNE). The photophysical and electrochemical studies showed that the incorporation of TCBD acceptor in the phenothiazine chromophores PTZs 12–15 facilitated the donor‐acceptor strength to greater extent. The electronic absorption spectra exhibited red shifted absorption bands for the TCBD substituted phenothiazines as compared to the alkynylated phenothiazines which led to much lower optical band gaps in the formers. The experimental values were also supported by the DFT and TD‐DFT calculations. [ABSTRACT FROM AUTHOR]

Using the density functional theory (DFT) formalism, we have investigated the properties of some arylsulphonyl indazole derivatives that we studied previously for their biological activity and susceptibility to interactions of azoles. This study includes the following physicochemical properties of these derivatives: electronegativity and polarisability (Mulliken charges, adjusted charge partitioning, and iterative-adjusted charge partitioning approaches); free energy of solvation (solvation model based on density model and M062X functional); highest occupied molecular orbital (HOMO)–lowest occupied molecular orbital (LUMO) gap together with the corresponding condensed Fukui functions, time-dependent DFT along with the UV spectra simulations using B3LYP, CAM-B3LYP, MPW1PW91, and WB97XD functionals, as well as linear response polarisable continuum model; and estimation of global chemical reactivity descriptors, particularly the chemical hardness factor. The charges on pyrrolic and pyridinic nitrogen (the latter one in the quinolone ring of compound 8, as well as condensed Fukui functions) reveal a significant role of these atoms in potential interactions of azole ligand–protein binding pocket. The lowest negative value of free energy of solvation can be attributed to carbazole 6, whereas pyrazole 7 has the least negative value of this energy. Moreover, the HOMO–LUMO gap and chemical hardness show that carbazole 6 and indole 5 exist as soft molecules, while fused pyrazole 7 has hard character.

The fluorescence coumarin derivatives were synthesised by an efficient one-pot, three-component reaction in 80–90% yields. The optical properties of these coumarin derivatives (4a-4d), such as the influence of different solvent to the fluorescence intensity and absorption intensity, and the influence of different substituent groups and the concentration of the solution are investigated. The results show that the fluorescence intensity of the compounds are the largest in the DMF（N,N-dimethyllformamide). Specifically speaking, the absorption spectrum is at approximately 308 nm, the fluorescence spectrum is at nearly 435 nm in the DMF, the Stocks shift approaches127 nm. In our case the fluorescence intensity decreases with the increase of the concentration of the solution, which is called concentration quenching. Additionally, the affection of solvent was also confirmed by TD-DFT (Time-dependent density functional theory)calculations.

The present study has been developing a robust quantum mechanical (QM) conformational sampling method (PrefQMCon) for optical reporting of 4‐anilinoquinazoline derivatives based epidermal growth factor receptor (EGFR) tyrosine kinases inhibitors. We use AG‐1478 to demonstrate how PrefQMCon helps QM determination of 22 target drug conformer clusters and their properties and UV–vis spectra. In this method, the preferred conformers of AG‐1478 are obtained by density functional theory (DFT) optimization from conformational local minimum sampling around the identified rotatable bonds, followed by clustering analysis and time‐dependent (TD) DFT calculations for the UV–vis spectra in solvents. Such obtained preferred conformers agree well with earlier experimental measurements where the conformer dependent UV–Vis spectral shift of AG‐1478 is as large as ~15 nm. We are further developing this PrefQMCon to study and design other 4‐anilinoquinazoline derivatives of EGFR TKIs. [ABSTRACT FROM AUTHOR]

The photoluminescence of Au(I) complexes is generally characterized by long radiative lifetimes owing to the large spin-orbital coupling constant of the Au(I) ion. Herein, we report three brightly emissive Au(I) coordination compounds, 1, 2a, and 2b, that reveal unexpectedly short emission lifetimes of 10–20 ns. Polymorphs 2a and 2b exclusively exhibit fluorescence, which is quite rare for Au(I) compounds, while compound 1 reveals fluorescence as the major radiative pathway, and a minor contribution of a microsecond-scale component. The fluorescent behaviour for 1–2 is rationalized by means of quantum chemical (TD)-DFT calculations, which reveal the following: (1) S0–S1 and S0–T1 transitions mainly exhibit an intraligand nature. (2) The calculated spin-orbital coupling (SOC) between the states is small, which is a consequence of overall small metal contribution to the frontier orbitals. (3) The T1 state features much lower energy than the S1 state (by ca. 7000 cm−1), which hinders the SOC between the states. Thus, the S1 state decays in the form of fluorescence, rather than couples with T1. In the specific case of complex 1, the potential energy surfaces for the S1 and T2 states intersect, while the vibrationally resolved S1–S0 and T2–S0 calculated radiative transitions show substantial overlap. Thus, the microsecond-scale component for complex 1 can stem from the coupling between the S1 and T2 states.

In this work, two families of Cu(I)-iodide complexes with N -heterocyclic donors ligands bearing amide, phenyl, chloro, and methyl substituents have been synthesized to combine two structural directing factors: attractive interactions and steric bulkiness. To this aim, we synthesized five Cu(I)-iodide based complexes: two 1D coordination polymers [CuI(isn)] n (1) and {[CuI(nic)]·ACN} n (2), one tetrameric cubane [CuI(3-phpy)] 4 (3), one rhomboid dimer [CuI(8-ClQuin)] 2 (4) and one monomer [CuI(1-CH 3 isoQuin)] (5). Interestingly, easy ligand dissociation and marked distortions within the molecular structure enabled structural rearrangements between the mentioned arrays. Then, we compiled the structures contained in this family of materials and provided a shape map and a conversion pathway between the most similar arrays, the cubane and the staircase polymer. Finally, the photophysical properties of 1 – 5 were investigated and electronic transitions were identified and supported by DFT and TD-DFT calculations since their photophysical properties are strongly dependent on the molecular arrangement and electronic distribution. One-pot synthesis using a combination of attractive interactions and steric hindrance template the arrangement of four Cu(I)-iodide arrangements which display emission in, the whole range of the visible spectra. Besides, theoretical calculations provide a further understanding of the electronic transitions. [Display omitted] • One-pot synthesis of Cu(I)-iodide based materials with N -donor ligands. • Strong interactions guided the molecular arrangement. • Cubanes and staircase polymers are prone to suffer structural transformations. • Importance of modeling in reproducing photophysical properties. • The packing drives emission in the whole range of the Visible spectrum. [ABSTRACT FROM AUTHOR]

We report synthesis, crystal structure, and photophysical properties of novel 1,3-phosphinoamines based on 4-amino-2,1,3-benzothiadiazole (NH2-btd): Ph2PCH(Ph)NH-btd (1) and Ph2P(E)CH(Ph)NH-btd, (E = O (2α and 2β·thf), S (3), Se (4)). Chalcogenides 2–4 exhibit bright emissions with a major band at 519–536 nm and a minor band at 840 nm. According to TD-DFT calculations, the first band is attributed to fluorescence, while the second band corresponds to phosphorescence. In the solid state, room temperature quantum yield reaches 93% in the case of the sulphide. The compounds under study feature effects of the molecular environment on the luminescent properties, which manifest themselves in fluorosolvatochromism as well as in a luminescent response to changes in crystal packing and in contributions to aggregation effects. Specifically, transformation of solid 2β·thf to solvate-free 2β either by aging or by grinding causes crystal packing changes, and, as a result, a hypsochromic shift of the emission band. Polystyrene films doped with 2 reveal a bathochromic shift upon increasing the mass fraction from 0.2 to 3.3%, which is caused by molecular aggregation effects.

The time‐dependent density functional theory was used to calculate the vibronic absorption spectrum of berberine (BER) in an aqueous solution. The best agreement with the experimental spectrum gives the O3LYP functional. Functionals with long‐range correction showed poor agreement with experiment. The molecular orbitals of BER involved in the electronic transition during light absorption in the visible spectral region have been obtained. The dipole moments and atomic charges of the ground and excited states of the BER molecule have been calculated. Maps of BER electron density and electrostatic potential have been drawn. A significant photoinduced electron transfer from the outer di‐oxygen five‐membered heterocycle to the center of the BER chromophore has been found. According to our calculations, vibronic coupling and Boltzmann distribution play a significant role in the absorption spectrum of BER. [ABSTRACT FROM AUTHOR]

The imino tautomers of isocytosine were objects of investigation at the TD-DFT level of theory - TD BLYP/6-311++G(d,p). We studied the mechanisms of the H1-N detachment in these tautomers through excited-state reaction paths. It was proposed that these transformations occur through the 1ps* excited-state reaction paths of the imino tautomers. The mechanisms involve dissociations of the N1-H bonds in the tautomers and lead to crossings between the reaction paths of 1ps* and S0 electronic states. One can suppose that such processes would facilitate the tautomerizations of the imino tautomers if further mechanisms have been found. [ABSTRACT FROM AUTHOR]

Functionalized octamers of polyaniline neutral forms (leucoemeraldine, emeraldine, pernigraniline) were studied in order to optimize the first hyperpolarizabilities (β). Remarkable static β values were found for the pernigraniline and emeraldine derivatives by using the coupled perturbed Kohn‐Sham (CPKS) approach at the PBE1PBE/6‐31G** level. The enhanced nonlinear response was achieved through the introduction of donor (D) and/or acceptor (A) groups into the oligoanilines structures. The nonlinear optical (NLO) properties of the octamers missing the substituent groups were also investigated. The largest β values were obtained for the pernigraniline and emeraldine derivatives having the tert‐butyl (D) and dicyanoethenyl (A) substituents at opposite ends, as well as the ones with only the acceptor group. These oligomers show charge transfer transitions with large oscillator strengths according to the time dependent density functional theory (TD‐DFT). Predicted β values for the majority of functionalized oligoanilines strongly indicate them as potential building blocks for molecular‐based nonlinear materials with second‐order response. [ABSTRACT FROM AUTHOR]

The quinazoline‐type ligand 2‐(4‐diethylamino‐2‐hydroxyphenyl)‐4‐methyl‐1,2‐dihydroquinazoline 3‐oxide (HL1; H is the deprotonatable hydrogen) was prepared. Two 2‐D supramolecular complexes [Cu2(L2)2(NO3)2] (1) and [Ni2(L2)2(CH3COO)2] (2) (L2 = 1‐(2‐{[(E)‐(4‐diethylamino‐2‐hydroxybenzylidene]amino} phenyl)ethanone oxime) were synthesized using HL1 and characterized by elemental analysis, spectroscopic methods, and single‐crystal X‐ray diffraction studies. It revealed that 1 had coordinated two nitrate ions whereas 2 had acetate ions. In the crystal structures, six‐coordinated Cu (II) complex 1 formed an infinite 2‐D and X‐shaped 3‐D supramolecular frameworks. Simultaneously, Ni (II) complex 2 assembled into wavy 2‐D networks. Furthermore, electrochemical properties and antimicrobial activities of all compounds were as well investigated. Afterwards, the electrophilic and nucleophilic attack sites identified by electrostatic potential (ESP) calculations confirmed that hydrogen bonds were observed in the optimized structure of the crystal, and the closest contact between the active atoms of both complexes was confirmed through Hirshfeld surface analysis and time‐dependent density functional theory (TD‐DFT) calculations. [ABSTRACT FROM AUTHOR]

We present the synthesis and analytical, spectroscopic and computational characterization of three amino-substituted benzo[b]thieno[2,3-b]pyrido[1,2-a]benzimidazoles as novel pH probes with a potential application in pH-sensing materials. The designed systems differ in the number and position of the introduced isobutylamine groups on the pentacyclic aromatic core, which affects their photophysical and acid-base properties. The latter were investigated by UV-Vis absorption and fluorescence spectroscopies and interpreted by DFT calculations. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are unionized at neutral pH, while their transition to monocationic forms occurs at pH values between 3 and 5, accompanied by substantial changes in spectroscopic responses that make them suitable for detecting acidic conditions in solutions. Computations identified imidazole imino nitrogen as the most favorable protonation site, further confirmed by analysis of perturbations in the chemical shifts of 1H and 13C NMR, and showed that the resulting basicity emerges as a compromise between the basicity-reducing effect of a nearby nitrile and a favorable contribution from the attached secondary amines. With this in mind, we designed a system with three amino substituents for which calculations predict pKa = 7.0 that we suggest as an excellent starting point for a potential pH sensor able to capture solution changes during the transition from neutral towards acidic media.

The photoisomerisation pathways of substituted aminoazobenzenes with cyano-containing acceptor moieties, AAB-DCV and AAB-TCV, are revealed by TD-DFT at B3LYP/6-31G** level. Stationary and transition points on ground and excited state potential energy surfaces are localised; both inversion and rotation trans- and cis-isomerisation mechanisms are considered and the former is shown to be the preferable for both chromophores in the ground state. UV/vis spectra of isomeric forms of AAB-DCV and AAB-TCV are calculated by TD-DFT in chloroform at CAM-B3LYP/PCM//def2-TZVP level, the effect of acceptors on the spectrum shape and absorption maximum is revealed. It is found that S0→S2 excitation determines the most intensive π-π* band in the case of AAB-DCV trans-isomer, while in the case of AAB-TCV this band is due to S0→S1 excitation. λmax is bathochromically shifted when passing from AAB-DCV to AAB-TCV for trans-isomers. As for cis-isomers, the spectrum shape is determined by several excitations up to S0→S4, corresponding transitions having close intensities. Switching ability of the composite nonlinear-optical polymer material is demonstrated at both molecular and macroscopic levels: first hyperpolarisability of trans- and cis-forms differs three times in favour of the former; estimations of macroscopic quadratic electric susceptibility, χ(2), performed for model PMMA-based doped materials reveal the corresponding almost twofold difference. [ABSTRACT FROM AUTHOR]

• Development of seven new pyranylidene-based organic dyes for DSSC applications. • Impact of the dye anchoring mode (mono- vs di-) on the photovoltaic performances. • Correlation between structural, electronic and photovoltaic properties of the dyes. • Mono-anchoring dye 17a exhibiting the highest power conversion efficiency of 5.23%. Mono- and di-anchoring γ-pyranylidene-based organic dyes featuring D–π–A and D–(π–A) 2 architectures have been engineered as sensitizers for applications in Dye-Sensitized Solar Cells (DSSCs). Their photophysical, electrochemical and photovoltaic properties were further investigated. TD-DFT calculations were performed to rationalize the trends observed in the optical and electrochemical properties of the dyes. The investigation of the photovoltaic performances of this series of new dyes provided structure–property relationships where their Power Conversion Efficiencies (PCE) could be correlated to structural features, such as the length of the π-conjugated spacer, the nature of the substituents on the pyranylidene electron donor moiety and the number of anchoring groups. Dye-Sensitized Solar Cells based on mono-anchoring dyes were more efficient than the corresponding cells based on di-anchoring analogues due to high dye loading. The highest Power Conversion Efficiency of 5.23% was achieved with the mono-anchoring 17a dye containing t -butyl substituent groups on the pyranylidene fragment and with one thienyl π-conjugated spacer. [ABSTRACT FROM AUTHOR]

In this paper, we report the synthesis and characterization of a series of phosphanyl‐substituted siloles. The chemical modification (oxidation, sulfurization, alkylation and complexation) results in a change in the energy levels of frontier orbitals, which has been studied by UV/Vis absorption spectroscopy and electrochemistry. Significantly, despite their high "s" character the phosphorus lone pairs of the 2,5‐bisphosphanylsilole can combine with the π‐system of the silole core resulting in a somewhat destabilized HOMO. The structural aspects of these new siloles have been investigated employing single‐crystal X‐ray diffraction and DFT calculations. [ABSTRACT FROM AUTHOR]