Analytical excited state gradients for time-dependent density functional theory plus tight binding (TDDFT + TB)

Understanding photoluminescent mechanisms has become essential for photocatalytic, biological, and electronic applications. Unfortunately, analyzing excited state potential energy surfaces (PESs) in large systems is computationally expensive, and hence limited with electronic structure methods such as time-dependent density functional theory (TDDFT). Inspired by the sTDDFT and sTDA methods, time-dependent density functional theory plus tight binding (TDDFT + TB) has been shown to reproduce linear response TDDFT results much faster than TDDFT, particularly in large nanoparticles. For photochemical processes, however, methods must go beyond the calculation of excitation energies. Herein, this work outlines an analytical approach to obtain the derivative of the vertical excitation energy in TDDFT + TB for more efficient excited state PES exploration. The gradient derivation is based on the Z vector method, which utilizes an auxiliary Lagrangian to characterize the excitation energy. The gradient is obtained when the derivatives of the Fock matrix, the coupling matrix, and the overlap matrix are all plugged into the auxiliary Lagrangian, and the Lagrange multipliers are solved. This article outlines the derivation of the analytical gradient, discusses the implementation in Amsterdam Modeling Suite, and provides proof of concept by analyzing the emission energy and optimized excited state geometry calculated by TDDFT and TDDFT + TB for small organic molecules and noble metal nanoclusters.

Synthesis, antimicrobial activity and molecular docking studies of spiroquinoline-indoline-dione and spiropyrazolo-indoline-dione derivatives

Spiro[benzo[h]quinoline-7,3'-indoline]diones and spiro[indoline-3,4'-pyrazolo[3,4-b]quinoline]diones were efficiently synthesized via one-pot multi-component reactions under ultrasound-promoted conditions. Spiro[benzo[h]quinoline-7,3'-indoline]dione derivatives were successfully developed by the reaction of isatins, naphthalene-1-amine and 1,3-dicarbonyl compounds. The spiro[indoline-3,4'-pyrazolo[3,4-b]quinoline]dione derivatives were prepared by the reaction of isatins, 5-amino-1-methyl-3-pheylpyrazole, and 1,3-dicarbonyl compounds by using ( ±)-camphor-10-sulfonic acid as a catalyst in H₂O/EtOH (3:1 v/v) solvent mixture. The antibacterial activity of the synthesized compounds was evaluated against, Enterococcus faecalis, Staphylococcus aureus and Candida albicans. Compounds 4b, 4h, and 6h showed the strongest antimicrobial activity toward both bacteria. The MIC values of these compounds ranged from 375-3000 µg/mL. The effect of these compounds (4b, 4h, 6h) as a function of applied dose and time was investigated by a kinetic study, and the interaction with these antimicrobial results was simulated by a molecular docking study. We also used the docking approach with Covid-19 since secondary bacterial infections. Docking showed that indoline-quinoline hybrid compounds 4b and 4h exerted the strongest docking binding value against the active sites of 6LU7. In addition, the synthesized compounds had a moderate to good free radical scavenging activity.

Photoinduced Synthesis of Functionalized Oxacyclic Spirooxindoles Via Ring Expansion

A versatile photochemical ring-expansion protocol for the synthesis of oxacyclic spirooxindoles under catalyst-free conditions is described. The reaction is enabled by the use of unstrained O-containing heterocycles with 3-diazoindolin-2-ones under visible-light irradiation. Several synthetic advantages for this method are exhibited, including mild conditions, good functional group tolerance, operational simplicity, and scalability. Mechanistic studies indicate that the transformation may proceed through the formation of oxonium ylide intermediate followed by an ionic cyclization.

Visible-light-mediated tandem phosphorylation/cyclization for the synthesis of phosphorylated oxindoles

The visible-light-mediated tandem phosphorylation/cyclization of N-arylacrylamides with H-phosphine oxides has been developed for the synthesis of phosphorylated oxindoles. This efficient and facile process was useful for the construction of a C-P bond and triggered the formation of a C-C bond with good compatibility with functional groups undermild reaction conditions.

Deciphering the dual emission in the photoluminescence of Au14Cd(SR)12: A theoretical study using TDDFT and TDDFT + TB

Determining excited state processes for small nanoclusters, specifically gold, aids in our ability to fine-tune luminescent materials and optical devices. Using TDDFT and TDDFT + TB, we present a detailed theoretical explanation for the dual emission peaks displayed in Au₁₄Cd(S-Adm)₁₂ (Adm = adamantane). As dual emission is relatively rare, we decipher whether the mechanism originates from two different excited states or from two different minima on the same excited state surface. This unique mechanism, which proposes that the dual emission results from two minima on the first excited state, stems from geometrical changes in the bi-tetrahedron core during the emission process.

Stereoselective formal [3 + 3] annulation of 3-alkylidene-2-oxindoles with β,γ-unsaturated α-keto esters

1,4-Diazabicyclo[2.2.2]octane (DABCO)-catalyzed [3 + 3] cycloaddition reaction of 3-alkylidene-2-oxindole and β,γ-unsaturated α-keto esters under mild reaction conditions afforded the spirocyclohexene-oxindole with excellent diastereoselectivity. The [3 + 3] annulation is found to proceed through a vinylogous Michael-aldol cascade reaction and it allows rapid access to a diverse set of highly functionalized spirocyclohexene-oxindoles. Also, a bioactivity study of the compounds on mammalian sarcoma cells has reflected cell growth inhibitory/anti-cancer properties.

Combined Scaffold Evaluation and Systems-Level Transcriptome-Based Analysis for Accelerated Lead Optimization Reveals Ribosomal Targeting Spirooxindole Cyclopropanes

With evolutionary drug resistance impacting efforts to treat disease, the need for small molecules that exhibit novel molecular mechanisms of action is paramount. In this study, we combined scaffold-directed synthesis with a hybrid experimental and transcriptome analysis to identify bis-spirooxindole cyclopropanes that inhibit cancer cell proliferation through disruption of ribosomal function. These findings demonstrate the value of an integrated, biologically inspired synthesis and assay strategy for the accelerated identification of first-in-class cancer therapeutic candidates.

Multi-component synthesis of fluorophores via catalytic generation of alkynoyl intermediates

This account summarizes recent developments of aggregation-induced emissive and emission solvatochromic fluorophores by multicomponent reactions. Key intermediates are catalytically generated alkynoyl derivatives that are directly transformed into luminophores in a one-pot fashion. The conciseness in combination with ready access to tailored chromophore libraries makes this synthetic methodological concept superior over classical multistep syntheses.

A Rhodium(II)-Catalyzed Formal [4+1]-Cycloaddition toward Spirooxindole Pyrrolone Construction Employing Vinyl Isocyanates as 1,4-Dipoles

A Rh^II -catalyzed, formal [4+1]-cycloaddition between diazooxindoles as electrophilic C₁ synthons and 1,3-heterodienes for the construction of spirooxindole pyrrolones is described. Employing vinyl isocyanates as 1,4-dipoles, the cycloannulation occurs under relatively mild conditions and provides the corresponding pyrrolones in good to excellent yields.

Molecular diversity of spirooxindoles. Synthesis and biological activity

Spirooxindoles are important synthetic targets possessing extended biological activity and drug discovery applications. This review focuses on the various strategies for the enantioselective synthesis of spirocyclic oxindoles relying on reports over the past decade and from earlier work. The spirooxindoles in this review are separated into three structural classes, and then further categorized into the method type from which the spirocycle is generated.

Diversity-oriented synthesis of intensively blue emissive 3-hydroxyisoquinolines by sequential Ugi four-component reaction/reductive Heck cyclization

A convergent approach to highly functionalized 3-hydroxyisoquinolines is reported. The key steps are an Ugi multicomponent reaction and a subsequent intramolecular reductive Heck reaction; these can also be performed as a one-pot procedure. The structures display very interesting properties as blue-fluorescence emitters. Photophysical studies on the absorption and static fluorescence indicate that the substitution pattern on the pyridyl part influences the optical properties only to a minor extent, unless the amide substituent becomes sterically demanding and leads to significant nonradiative deactivation. The donor substitution on the benzo core considerably enhances the fluorescence quantum yields and trimethoxy substitution causes a pronounced redshift of the emission bands. Protonation of the isoquinolyl nitrogen atom causes efficient static quenching of the fluorescence.

One-pot three-component synthesis and photophysical characteristics of novel triene merocyanines

Novel triene merocyanines, i.e. 1-styryleth-2-enylidene and 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are obtained in good to excellent yields in a consecutive three-component insertion Sonogashira coupling-addition sequence. The selectivity of either series is remarkable and has its origin in the stepwise character of the terminal addition step as shown by extensive computations on the DFT level. All merocyanines display intense absorption bands in solution and the film spectra indicate J-aggregation. While 1-styryleth-2-enylideneindolones show an intense deep red emission in films, 4-(1,3,3-trimethylindolin-2-ylidene)but-2-en-1-ylideneindolones are essentially nonemissive in films or in the solid state. TD-DFT computations rationalize the charge-transfer nature of the characteristic broad long-wavelength absorptions bands.

Highly stereoselective generation of complex oxy-bicyclic scaffolds via an atom-economic Pd(II)-catalyzed hydroalkynylation, isomerization and Diels-Alder cycloaddition sequence

An atom-economic tandem Pd(II)-catalyzed hydroalkynylation, alkyne-allene isomerization, and Diels-Alder cycloaddition is reported. The reaction employs readily available starting substrates, proceeds in a highly ordered fashion, features high regio- and stereoselectivity, and tolerates a wide range of functionality and structural motifs, thus offering an attractive strategy for producing new molecular complexity and diversity from easily available starting materials. A mechanistic study with density functional theoretical calculations was conducted to rationalize the observed stereoselectivity.