Time-dependent Density Functional Theory Study Research Articles

Metal Free Approach towards the Synthesis of Structurally Diverse 1, 2‐Dihydronaphthalene Scaffolds and Theoretical Investigation

AbstractBiologically potent and synthetically significant 1,2‐dihydronaphthalene derivatives have gained considerable attention due to their wide applications in industrial as well as in medicinal fields also. A mild and efficient metal‐free protocol via the rearrangement of cyclopropylcarbinols has been reported to construct these 1,2‐dihydronaphthalene skeletons utilizing cyclopropane ring as the scaffold. We obtained conjugated dienes and, in some cases, homoallylic chlorides as major products in good to excellent yields. They have no literature precedence till date. The fate of this rearrangement depends on the substituent patterns of the cyclopropane bearing aryl moiety. Besides the synthetic studies, to get deep insight into the electronic transitions, time dependent DFT studies have also been performed.

DFT and TDDFT studies of structural, electronic and optical properties of the inorganic solar perovskites XPbBr3 (X = Li or Na)

ABSTRACT In this paper, we study the structural, electronic and optical properties of the inorganic solar perovskites XPbBr3 (X = Li or Na). We applied the two methods: the density-functional theory (DFT) and time-dependent density-functional theory (TDDFT). In fact, we performed the DFT method using the Quantum Espresso package. Also, the total energies of the studied inorganic solar perovskites XPbBr3 (X = Li or Na) have been deduced as a function of the lattice parameter a (Å). The two calculation methods have been carried out under the GGA-PBE and GGA-PBESol approximations. Moreover, the total and partial density of states (DOS) and the band structure of the studied compounds have been presented and discussed for the two cases: with and without the spin-orbit coupling (SOC) approximation. In addition, the DFT and TDDFT have been explored in order to elaborate the structural, the electronic and the optical properties of the inorganic perovskite CsPbI3 material.

Enhanced energy transfer from diolefinic laser dyes to meso-tetrakis (4-sulfonatophenyl) porphyrin immobilized on silver nanoparticles: DFT, TD-DFT and spectroscopic studies

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.

A DFT and TD-DFT study on emodin and purpurin and their functionalized molecules to produce promising organic semiconductor materials

Density functional theory (DFT) computations were done to explore the optical and electronic properties of two conjugated molecules, emodin and purpurin, as potential organic semi-conductors. The molecules were functionalized to explore the impact of functionalization on the electronic and optical properties. The properties calculated include reorganization energy (λh and λe), adiabatic ionization potential (IP), adiabatic electron affinity (EA), chemical hardness (n), HOMO and LUMO energies, and HOMO-LUMO energy gap (Eg) via B3LYP/6–3++G (d, p) method. In addition, the maximum absorption (λmax) and oscillator strength (f) at the excited states in vacuum and solvent (Ethanol) were investigated using time-dependent density functional theory (TD-DFT). The introduction of functional groups to emodin was considered to convert the molecule from a p-type into an n-type material, while purpurin is considered as an n-type material, its functionalization with NO2 and 2F resulted in a slight increase in λe values, which is considered detrimental for the process of charge-transport. However, the functionalized molecules have shown an increase in EA and a decrease in LUMO energy level, indicating their potential use as n-type materials. Furthermore, to have an understanding of the intermolecular interactions in emodin and purpurin molecules, Hirshfeld surface analysis and energy framework were studied.

Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies.

Aggregation-induced emission (AIE) has gained a remarkable amount of interest in the past 20 years, but the majority of the studies are based on organic structures. Herein, three dinuclear gold(I) complexes, with the general formula [PPh2XPPh2-Au2-Coum2], where the Au(I) atom is linked to three different diphosphanes [PPh2XPPh2; DPPM for X = CH2 (1.1), DPPP for X = (CH2)3 (1.2), and DPPA for X = C≡C (1.3)] and the propynyloxycoumarin precursor (1, 4-methyl-substituted coumarin), have been synthesized. The compounds present AIE characteristics, AIEgens, with high luminescence quantum yields in the solid state when they are compared to dilute solutions. Photophysical studies (steady-state and time-resolved fluorescence) were obtained, with AIE being observed with the three gold(I) complexes in acetonitrile/water mixtures. This was further corroborated with dynamic light scattering measurements. Time-dependent density functional theory (TDDFT) electronic calculations show that the compounds have different syn and anti conformations (relative to the coumarin core) with 1.1 syn and 1.2 and 1.3 both anti. From time-resolved fluorescence experiments, the augment in the contribution of the longer decay component is found to be associated with the emission of the aggregate (AIE effect) and its nature (involving a dimer) rationalized from TDDFT electronic calculations.

Ab initio study of ultrafast demagnetization of elementary ferromagnets by terahertz versus optical pulses

We present an ab initio time-dependent density functional theory study of the ultrafast demagnetization of elemental ferromagnets subject to terahertz (THz) laser pumping compared to optical laser pumping. We find that THz radiation can cause as much demagnetization as optical radiation for significantly lower-energy transfer to the sample. We show that the demagnetization efficiency of the THz pulse is related to a coherent coupling of the radiation to the electron charge dynamics. In fact, our simulations reveal that the low-frequency THz electric field enforces in-phase electron charge oscillations around the atomic centers, leading to a highly efficient spin-orbit torque switching of the magnetization. Unlike for optical pumping, at the end of the pulse a major fraction of the excited electrons is driven back to equilibrium acquiring a thermalized Fermi-Dirac distribution.

Synthesis and Characterization of Pyridine Dipyrrolide Uranyl Complexes.

The first actinide complexes of the pyridine dipyrrolide (PDP) ligand class, (MesPDPPh)UO2(THF) and (Cl2PhPDPPh)UO2(THF), are reported as the UVI uranyl adducts of the bulky aryl substituted pincers (MesPDPPh)2– and (Cl2PhPDPPh)2– (derived from 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2MesPDPPh, Mes = 2,4,6-trimethylphenyl), and 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2Cl2PhPDPPh, Cl2Ph = 2,6-dichlorophenyl), respectively). Following the in situ deprotonation of the proligand with lithium hexamethyldisilazide to generate the corresponding dilithium salts (e.g., Li2ArPDPPh, Ar = Mes of Cl2Ph), salt metathesis with [UO2Cl2(THF)2]2 afforded both compounds in moderate yields. The characterization of each species has been undertaken by a combination of solid- and solution-state methods, including combustion analysis, infrared, electronic absorption, and NMR spectroscopies. In both complexes, single-crystal X-ray diffraction has revealed a distorted octahedral geometry in the solid state, enforced by the bite angle of the rigid meridional (ArPDPPh)2– pincer ligand. The electrochemical analysis of both compounds by cyclic voltammetry in tetrahydrofuran (THF) reveals rich redox profiles, including events assigned as UVI/UV redox couples. A time-dependent density functional theory study has been performed on (MesPDPPh)UO2(THF) and provides insight into the nature of the transitions that comprise its electronic absorption spectrum.

Synthesis, characterization and biological properties of Ruthenium(II) polypyridyl complexes containing 2(1H)-quinolinone-3(1H-imidazo[4,5f][1,10]phenanthrolin-2-yl

The ruthenium(II) complexes have been structurally characterised and their interaction with DNA, cytotoxicity and cellular uptake has been investigated. • Two water-soluble ruthenium(II) polypyridyl complexes were synthesized and characterized. • The complexes show solvent-dependent photophysical properties and are highly emissive in aqueous solutions. • The ruthenium(II) complexes exhibited moderate DNA binding ability. • Ruthenium(II) complexes are non-toxic towards HeLa cell line. • The ruthenium(II) complexes undergo rapid cellular internalization and localized throughout the cells. Two water-soluble ruthenium(II) polypyridyl complexes [Ru(bpy) 2 (qip)]Cl 2 ( 1 ) and [Ru(phen) 2 (qip)]Cl 2 ( 2 ) (where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, qip = 2(1H)-quinolinone-3(1H-imidazo[4,5f][1,10]phenanthrolin-2-yl) have been synthesized and structurally characterized. The experimental electronic spectral results obtained match well with the theoretical results obtained by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) studies. For both the complexes HOMO is mainly localized on the ancillary qip ligand, while HOMO-1 is mainly centered on the ruthenium atom with some contribution from all polypyridyl ligand. The LUMO is located on all polypyridyl ligands. Interaction of complexes with CT-DNA is explored by absorption and emission spectroscopic techniques. The complexes show solvent-dependent photophysical properties and are highly emissive in aqueous solutions compared to organic solvents. Both the complexes are non-toxic towards HeLa (human cervical cancer) and HEK293 (human embryonic kidney cell line) cell lines. Further, the cellular imaging properties of complexes 1 and 2 were investigated by fluorescence microscopy.

Estimation of Electron Distribution over Dinuclear Organometallic Molecular Wires by "IR Tag" Analysis of Ancillary Acyl-Cp Ligands.

Understanding the details of electronic properties of mixed-valence (MV) states of organometallic molecular wires is essential to gain insights into electron transfer phenomena. Although the field of MV chemistry is matured, there remain issues to be solved, which cannot be accessed by the conventional analytical methods. Here, we describe the synthesis and properties of diruthenium bridging (diethynylbenzene)diyl wires, (μ-p and m-C≡C-C6H4-C≡C){RuCpR(dppe)}2 1, with the acyl-substituted cyclopentadienyl rings [CpR: Cpe; η5-C5H4COOMe (a-series: ester derivatives), Cpa; η5-C5H4COMe (b-series: acetyl derivatives)], which are installed as IR-tags to estimate electron densities at the metal centers in the MV species. The electrochemical and IR/near IR-spectroelectrochemical studies reveal that the two metal centers in the para-isomers p-1a,b + interact with each other more strongly than those in the meta-isomers m-1a,b + . Electron-spin resonance study also supports the radicals being delocalized over the Ru-(p-C≡C-C6H4-C≡C)-Ru moieties in p-1a,b + . The spectroelectrochemical IR study shows significant higher-energy shifts of the ν(C=O) vibrations brought about upon 1e-oxidation. Spectral simulation on the basis of the Bloch equations allows us to determine the electron transfer rate constants (k et) between the two metal centers being in the orders of 1012 s-1 ( p-1 + ) and 109 s-1 ( m-1 + ). The shifts of the ν(C=O) bands reveal that the charge densities on the para-isomers p-1a,b + are widely delocalized over the Ru-(p-C≡C-C6H4-C≡C)-Ru linkages in contrast to the meta-isomers m-1a,b + , where the electron densities are mainly localized on the metal fragments, as supported by the density functional theory and time-dependent density functional theory studies as well as comparison with the reference mononuclear acetylide complexes, C6H5-C≡C-RuCpR(dppe) 2. We have successfully demonstrated that the carbonyl groups (>C=O) in the ancillary Cp ligands also work as IR-tags to report detailed information on the electron densities at the metal centers and the electron distribution over MV complexes as well.

Solvation-controlled emission of divalent europium salts

Coordination-environment-dependent tuning of luminescence of divalent europium is an emerging topic of research. While it has been extensively demonstrated in the solid state, recent reports indicate similar findings in solution, where emission properties were tuned by altering different ligands and counter anions. In the present study, we demonstrate that differences in solvation shells alter the luminescence properties of divalent europium. Steady-state emission measurements indicate that the emission maxima of EuII salts in dimethoxyethane is red-shifted compared to the maxima in tetrahydrofuran. This shifting was confirmed with three different EuII salts: EuI2, EuBr2, and Eu(OTf)2. UV–visible spectroscopic measurements indicate a marginal difference in absorption spectra of EuII salts in tetrahydrofuran and dimethoxyethane, ruling out the possibility that a difference in ground-state geometry is responsible for the solvation-induced emission shift. Time-dependent density functional theory studies further support this conclusion. Relaxation of the excited state in dimethoxyethane is a postulated mechanism behind the red-shifted emission. The current study demonstrates a straight-forward path toward tuning the emission properties of EuII without altering light absorption.

Experimental and theoretical study of organic sensitizers for solid-state dye-sensitized solar cells (s-DSSCs)

The effect of a series of triarylamine based D-π-A organic dyes, namely RK1, BA504, BA741 and the simple L1 reference dye on solid-state dye sensitized solar cells (s-DSSCs) performances was studied. The solid hole transporting material (HTM) was obtained by in-situ photoelectrochemical polymerization (in-situ PEP) process applied in two different media (water and acetonitrile) to produce the poly-3,4 ethylenedioxythiophene (PEDOT) conducting polymer (CP). A joint experimental and theoretical (density functional theory and time-dependent density functional theory) study is conducted to correlate the dye molecular structure containing different donor, π-bridge or acceptor with several physicochemical characteristics such as optical (absorption and emission), electronic and redox properties of dyes in organic and aqueous medium; in-situ PEP process and charge transfer kinetics at the DSSC interfaces (Dye/TiO2 and Dye/HTM) through the alignment of the different energy levels of the dyes and electrodes. These properties are considered since they govern the performance of s-DSSCs denoted by the short-circuit current (Jsc), open circuit cell potential (Voc) and fill factor (FF). Among the four studied dyes, the s-DSSCs based on RK1, shows the best power conversion efficiency of 1.75% resulting from highest FF (0.57), Voc (550 mV) and Jsc (5.6 mA/cm2). The large differences in experimental photovoltaic performances of the obtained s-DSSCs have been well outlined and provide the guidelines for future development of more efficient solar-cell sensitizers.

Proton-transfer reactions of Re(II)-nitrosyl complexes: Potentiometric studies, DFT and TD-DFT calculations

In the present work, we investigated the proton-transfer reactions of Re(II)-nitrosyl complexes bearing halides and nicotinic acid (Hnic) or 6,6́-dinicotinic acid (H2dinic) trans-coordinated to the core {ReNO}3+ by potentiometry and UV − Vis absorption spectroscopy in a mixture DMSO:H2O (1:1; v:v). The presence of Hnic and H2dinic in title complexes promotes a marked decrease in the acidity (higher pK values) compared to the non-coordinated pyridine-derived ligands. The UV − Vis measurements indicate that the absorption spectra of complexes do not show any dependence on the acidity of the medium and the number of non-coordinated carboxylic units. Time-dependent Density Functional Theory (TD-DFT) calculations are performed to understand the optical properties of complexes and their response upon deprotonation. TD-DFT studies are conducted with PBE1PBE in combination with LANL2TZ on rhenium and 6–311++G(d,p) on non-metal atoms within the C-PCM approach. This methodology shows a reasonable match between the measured and simulated spectra keeping the computational cost low. The nature of all absorption bands is ascribed to a ligand-metal-to-ligand-metal charge transfer (LMLMCT), in which negligible contribution from carboxylic units is detected.

Ab-Inito Simulation of the Structural, Electronic and Optical Properties for the Vacancy-Ordered Double Perovskites A2tii6 (a = Cs and Nh4); a Time-Dependent Density Functional Theory Study

Ab-Inito Simulation of the Structural, Electronic and Optical Properties for the Vacancy-Ordered Double Perovskites A2tii6 (a = Cs and Nh4); a Time-Dependent Density Functional Theory Study

Similarity and Dissimilarity between Water and Methanol in Solvent Effects on the Spectroscopic Properties of Aniline: Molecular Dynamics and Time-Dependent Dft Studies

Similarity and Dissimilarity between Water and Methanol in Solvent Effects on the Spectroscopic Properties of Aniline: Molecular Dynamics and Time-Dependent Dft Studies

Revealing the synergetic interaction between amino and carbonyl functional groups and their effect on the electronic and optical properties of carbon dots.

Nitrogen and oxygen-based functionalized carbon dot (CDs) surfaces have attracted significant attention due to their ability to tailor the optical and electronic properties of CDs. However, the complex synthesis process and structure of the functionalized CDs hinder an in-depth understanding of their mechanism, limiting their potential applications. Herein, we report CDs functionalized with amino and carbonyl functional groups and reveal the mechanism of interaction between the amino and carbonyl groups and the CDs' optical and electronic properties. Both Time-dependent Density Functional Theory (TD-DFT) and experimental studies revealed that the synergetic effects between amino and carbonyl groups significantly shift the absorption peaks to the NIR region and strengthen their absorption intensity. Furthermore, their absorption and bandgap energy could be tuned by optimizing the amino to carbonyl ratio on CDs surfaces. This study suggests that amino and carbonyl groups synergistically tailor the CDs' optical and electronic properties through frontier orbital hybridization and high charge transfer. This knowledge opens a new avenue for tailoring the desired optical and electronic properties of CDs for any application.

Efficient tuning of benzocarbazole based small donor molecules with D-π-A-π-D configuration for high-efficiency solar cells via π-bridge manipulation: A DFT/ TD-DFT study

Nine new donor molecules BCi (i = 1–9) of type D-π-A-π-D are explored to study their application to improve the efficiency of OSCs. These designed molecules contain a central diketopyrrolopyrrole acceptor linked to two terminal benzocarbazole donors by different π-bridges. Using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, various parameters like FMO, NBO, DOS analysis, absorption maxima, and ICT parameters have been estimated to evaluate the performance of newly designed molecules. Our investigations reveal that the modification of the π-bridges has a great effect on the optoelectronic and photovoltaic properties of the compounds. In this regard, it should be noted that the donor molecule BC6 with the π-spacer moiety thiazolothiazole exhibits a narrow band gap, a broad absorption spectrum, a better LHE, a lower values for λtot, ΔEL-L and chemical parameters, an acceptable Voc and a higher value of EA. Thus, they can be utilized as an electron-donating in photovoltaic applications.

A study of the complexes of Hg(II) with polypyridyl ligands by Fluorescence, absorbance Spectroscopy, and DFT calculations. The effect of ligand preorganization and relativistic effects on complex stability

The formation of complexes of Hg(II) with the tetradentate polypyridyl ligands (L) qpy (2,2′:6′, 2′':6′',2′''-quaterpyridine), DPP (2,9-di-2-pyridinyl-1,10-phenanthroline), biphen (2,2′-bi-1,10-phenanthroline), and ebip (diquino[8,7-b:7′,8′-j][1,10]phenanthroline, 8,9-dihydro­), and the tridentate tpy (2,2′:6′,2′'-​terpyridine) is monitored by absorbance and fluorescence spectroscopy. The pH-dependence studies of fluorescence showed complete quenching of all fluorescence until the spectra of the free non-protonated ligands appeared at pH ≥ 9, attributed to the equilibrium Hg(L)22+ + 2 OH– ⇆Hg(OH)2 + 2 L. The absorbance titrations were carried out between pH 2 and 12 with 10-5 M L and 10-5 M or 5 × 10-6 M Hg(ClO4)2 to give 1:1 or 2:1 L:Hg ratios. These also showed the above hydrolysis of the HgL22+ complexes by hydroxide to give Hg(OH)2 at the higher pH values, but showed other equilibria at lower pH not apparent in the fluorescence titrations. At pH values around 7 a pH dependent equilibrium attributed to formation of the HgL22+ from the HgL2+ complexes was observed: HgL2+ + 2 OH– ⇆Hg(OH)2 + HgL22+. At around pH 2–3 a further equilibrium was observed, assigned to HgL2+ + H+ ⇆HgLH3+. Analysis of all these titrations gave log K1 values with Hg(II) as follows (ionic strength zero, 25 °C): qpy, 18.0; DPP, 18.7; biphen, 20.4; ebip, 21.8, where log β2 values are qpy, 24.0; DPP, 28.0; biphen, 28.6; ebip, 30.8. For the tridentate tpy complexes of Hg(II) log β 2 of 23.3 was obtained, but very little of the HgL2+ complex appeared to be present, with the [Hg(tpy)2]2+ complex plus Hg(OH)2 (aq) dominating. Only an estimate of log K1 ∼ 10.6 for Hg(II)/tpy could be obtained. The effect of increasing preorganization of the ligands along the series qpy < DPP < biphen < ebip in increasing complex stability of the Hg(II) is discussed. For the Hg(DPP)2+ and Hg(DPP)22+ complexs, DFT and Time-dependent DFT studies were also carried out to further confirm the formation of 2:1 complexes and identify the corresponding coordination geometry of Hg(II) in Hg/DPP complexes.

Unprecedented platinum(II) coordination compound of sterically hindered 3,3′-bis(NH-benzimidazol-2-yl)-2,2′-bipyridine ligand

The synthesis, spectroscopic characterization, single-crystal X-ray diffraction (SCXD) analysis, and Density Functional Theory (DFT) and time-dependent DFT (TD-DFT) studies of the coordination compound of cis-dichloroplatinum(II) with a sterically hindered N4-donor ligand, 3,3′-bis(NH-benzimidazol-2-yl)-2,2′-bipyridine (L), [Pt(L)Cl2]⋅DMSO (1) (DMSO = dimethyl sulfoxide) are reported. The Pt(II) ion adopts a slightly distorted square-planar geometry in which L coordinates in a bidentate fashion to the metal center through N atom of benzimidazole (bim) and N atom of pyridine (py) to form a seven-membered ring. The molecular units in the lattice are held together in a head to tail fashion as a dimer through intermolecular hydrogen bonding between the uncoordinated bim and py rings in the molecule through N H⋅⋅⋅N hydrogen bonds with the R22 (14) graph-set motif. The lattice DMSO solvent molecule significantly stabilizes the structure through N H⋅⋅⋅O hydrogen bond with the coordinated bim in the structure. Hirshfeld surface analysis also confirmed the hydrogen bond interactions in the crystal. DFT and TD-DFT results show that optimized geometry and UV-vis absorption spectra are consistent with the experimental results. Natural bond orbital (NBO) properties show that the hydrogen bond stability between the two monomers attributes with large stabilization energy values.

Fabrication of nanohybrids toward improving therapeutic potential of a NIR photo-sensitizer: An optical spectroscopic and computational study

Implementation of near infrared radiation (NIR) active drugs in photodynamic therapy (PDT) is considered as a highly promising tool in therapeutic application. Because of its strong NIR absorbance, indocyanine green (ICG) has become an attractive choice in emerging photo-theranostics. ICG generates singlet oxygen as well as shows photothermal effect under NIR irradiation. However, ICG is unable to produce sufficient amount of others types of reactive oxygen species (ROS) such as superoxide, hydroxyl radical. But, its ability of singlet oxygen generation under NIR irradiation is arrested by its tendency to aggregate in aqueous medium. Because of this limitation, it shows better effectiveness in photothermal therapy compare to it’s action as a photodynamic agent. Herein, we have addressed to overcome this limitation via the fabrication of zinc oxide (ZnO) based ICG-ZnO nanohybrid which provides lesser H-aggregation between ICG molecules on its surface and yield significantly greater amount of ROS relative to ICG upon photoexcitation, due to excited state electron transfer from ICG to ZnO. Also, this surface functionalization prevents aggregation of ICG in water significantly. Classical MD simulation shows the dimeric structure of ICG breakes down on ZnO surface which corroborates results from the aggregation study in water. Density functional theory (DFT) along with time-dependent DFT studies elucidate that upon photoexcitation electron transfer takes place from the higher energy orbital of ICG to the conduction band of ZnO. The greater efficiency in ROS generation by the ICG-ZnO nanohybrid than ICG or ZnO demonstrates remarkable antimicrobial activity against gram-negative bacteria E. coli. Overall, the present study highlights the scope of developing ICG-ZnO nanohybrid as a highly efficient NIR agent for use in antibacterial photodynamic therapy.

Harnessing Bismuth Coordination Chemistry to Achieve Bright, Long-Lived Organic Phosphorescence.

A new bismuth(III)-organic compound, Hphen[Bi2(HPDC)2(PDC)2(NO3)]·4H2O (Bi-1; PDC = 2,6-pyridinedicarboxylate and phen = 1,10-phenanthroline), was synthesized, and the structure was determined by single-crystal X-ray diffraction. The compound was found to display bright-blue-green phosphorescence in the solid state under UV irradiation, with a luminescent lifetime of 1.776 ms at room temperature. The room temperature and low-temperature (77 K) emission spectra exhibited the vibronic structure characteristic of Hphen phosphorescence. Time-dependent density functional theory studies showed that the excitation pathway arises from an energy transfer from the dimeric structural unit to Hphen, with participation from a nine-coordinate Bi center. The triplet state of Hphen is believed to be stabilized via supramolecular interactions, which, when coupled with the heavy-atom effect induced by Bi, leads to the observed long-lived luminescence. The compound displayed a solid-state quantum yield of over 27%. To the best of our knowledge, this is the first such compound to exhibit phenanthrolinium phosphorescence with such long-lived, room temperature lifetimes in the solid state. To further elucidate the energy-transfer mechanism, Ln3+ (Ln = Eu, Tb, Sm) ions were successfully doped into the parent compound, and the resulting materials exhibited dual emission from Hphen and Ln, promoting tunability of the emission color.