Quantum chemical investigation of electronic transitions of mitorubrin azaphilones.

Fungal azaphilones are a broad class of naturally-occurring pigments with diverse applications. Among the azaphilone pigments, mitorubrins are well recognized for their antiviral, antibacterial, antifungal, antiprotozoal, antidiabetic, and antiaging activities in addition to their well-known yellow-orange color. This makes these pigments interesting candidates for use in foods, as cosmetics, and as medicines. In particular, if it is desired to modify the properties of mitorubrin-based pigments, for example by derivatization, it is essential to have an understanding of the electronic spectra of the parent molecules. We have therefore undertaken a computational study of a series of mitorubrins, comparing our computed results with experimental UV/visible spectra. Both density-functional theory (DFT) and coupled-cluster (CC2) methods have been used, and in general, the results are in very good agreement with observation. In order to provide a simple and useful picture of the spectra we analyze the stronger transitions in terms of natural transition orbitals (NTOs).

Modeling the polychromism of oxide minerals: The case of alexandrite and cordierite.

In this work, we investigate the spectroscopic properties of photochromic alexandrite and cordierite by TD-DFT. The objective is to assess the TD-DFT for the simulation of pleochroism (change of color depending on the crystallographic direction of the observation) and the change of color as a function of the light source. For these simulations, we compared an embedding where dangling bonds are saturated by hydrogen atoms and an electrostatic embedding. The electrostatic embedding provided numerically more stable results and allowed a good reproduction of the pleochroism of cordierite, based on a Fe2+-Fe3+ intervalence charge transfer transition. However, the pleochroism of alexandrite is not as well reproduced, suggesting that TD-DFT has some difficulties to reproduce the anisotropy of the transition dipole moment, an aspect that is not deeply documented in the literature.

Tuning ultrafast time-evolution of photo-induced charge-transfer states: A real-time electronic dynamics study in substituted indenotetracene derivatives.

Photo-induced charge transfer (CT) states are pivotal in many technological and biological processes. A deeper knowledge of such states is mandatory for modeling the charge migration dynamics. Real-time time-dependent density functional theory (RT-TD-DFT) electronic dynamics simulations are employed to explicitly observe the electronic density time-evolution upon photo-excitation. Asymmetrically substituted indenotetracene molecules, given their potential application as n-type semiconductors in organic photovoltaic materials, are here investigated. Effects of substituents with different electron-donating characters are analyzed in terms of the overall electronic energy spacing and resulting ultrafast CT dynamics through linear response (LR-)TD-DFT and RT-TD-DFT based approaches. The combination of the computational techniques here employed provided direct access to the electronic density reorganization in time and to its spatial and rational representation in terms of molecular orbital occupation time evolution. Such results can be exploited to design peculiar directional charge dynamics, crucial when photoactive materials are used for light-harvesting applications.

Orthogonal effect of exchange and correlation parameters in density functional theory to compute geometric and spectroscopic quantities.

The influence of the composition of the functional used for density functional theory computations on one structural parameter (a dihedral angle) and a spectroscopic parameter (absorption wavelength) is assessed in this study on the basis of two molecules (flavonols). In this kind of molecules, these two parameters should be correlated according to the nature of the electronic transition involved. However, it is shown herein that by varying the proportion of true exchange and correlation while building a functional, it is possible to obtain independently a large range of values for these parameters without any relation with the underlying real values. Therefore, it is concluded that the choice of a functional after a benchmark, especially using user-defined functionals, should be carried out with great care to avoid such effects.

Ruthenium complexes bearing nile red chromophore and one of its derivative: Theoretical evaluation of PDT-related properties.

The outcomes of DFT-based calculations are here reported to assess the applicability of two synthesized polypyridyl Ru(II) complexes, bearing ethynyl nile red (NR) on a bpy ligand, and two analogues, bearing modified-NR, in photodynamic therapy. The absorption spectra, together with the non-radiative rate constants for the S1 - Tn intersystem crossing transitions, have been computed for this purpose. Calculations evidence that the structural modification on the chromophore destabilizes the HOMO of the complexes thus reducing the H-L gap and, consequently, red shifting the maximum absorption wavelength within the therapeutic window, up to 620 nm. Moreover, the favored ISC process from the bright state involves the triplet state closest in energy, which is also characterized by the highest SOC value and by the involvement of the whole bpy ligand bearing the chromophore in delocalising the unpaired electrons. These outcomes show that the photophysical behavior of the complexes is dominated by the chromophore.

Unraveling the structure-property relationship of novel thiophene and furan-fused cyclopentadienyl chromophores for nonlinear optical applications.

Development of organic nonlinear optical materials has become progressively more important due to their emerging applications in new-generation photonic devices. A novel series of chromophores based on innovative thiophene and furan-fused cyclopentadienyl bridge with various powerful donor and acceptor moieties were designed and theoretically investigated for applications in nonlinear optics. To unravel the structure-property relationship between this new push-pull conjugated systems and their nonlinear optical property, multiple methods, including density of states analysis, coupled perturbed Kohn-Sham (CPKS) method, sum-over-states (SOS) model, the two-level model (TSM), hyperpolarizability density analysis, and the (hyper)polarizability contribution decomposition, were performed to comprehensively investigated the nonlinear optical and electronic properties of this new π-system. Due to excellent charge transfer ability of new bridge and distinctive structure of donor and acceptor, the designed chromophores exhibit deep HOMO levels, low excitation energy, high dipole moment difference and large hyperpolarizability, indicating the appealing air-stable property and remarkable electrooptic performance of them. Importantly, THQ-CS-A3 and PA-CS-A3 shows outstanding NLO response properties with ßtot value of 6953.9 × 10-30 and 5066.0 × 10-30 esu in AN, respectively. The influence of the push-pull strength, the heterocycle and the π-conjugation of new bridge on the nonlinear optical properties of this novel powerful systems are clarified. This new series of chromophores exhibit remarkable electro-optical Pockels and optical rectification effect. More interestingly, PA-CS-A3 and THQ-CS-A2 also show appealing SHG effect. This study will help people understand the nature of nonlinear optical properties of innovative heteroarene-fused based cyclopentadienyl chromophores and offer guidance for the rational design of chromophores with outstanding electrooptic (EO) performance in the future.

Chiral Spiro-Tetrathiafulvalenes: Synthesis, Chiroptical Properties, Conformational Issues and Charge Transfer Complexes.

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.

Exploring the Theoretical Foundations of Thermally Activated Delayed Fluorescence (TADF) Emission: A Comprehensive TD-DFT Study on Phenothiazine Systems.

This study conducts a thorough theoretical investigation of Thermally Activated Delayed Fluorescence (TADF) in phenothiazine-based systems, examining ten molecular configurations recognized experimentally as TADF-active. Employing Time-Dependent Density Functional Theory (TD-DFT), our analysis spans the investigation of singlet-triplet energy gaps (ΔEST), spin-orbit coupling, and excitation characteristics using Multiwfn. This approach not only validates the adherence to El Sayed's rule across these systems but also provides a detailed understanding of charge transfer dynamics, as visualized through heat maps. A significant aspect of our study is the exploration of different oxidation states of sulfur and site substitutions on phenothiazine. This systematic variation aims to identify additional TADF-active compounds, drawing parallels with properties characterizing other known TADF emitters. Our investigation into Reverse Intersystem Crossing (rISC) rates and the analysis of dihedral angles in relation to ΔEST values offer nuanced insights into the TADF behaviours of these molecules. By integrating rigorous computational analysis with practical implications, we provide a foundational understanding that enhances the design and optimization of phenothiazine-based materials for optoelectronic applications. This work not only advances our theoretical understanding of TADF in phenothiazine derivatives but also serves as a guide for experimentalists and industry professionals in the strategic design of new TADF materials.

Enhancing the Potential of Fused Heterocycle-Based Triarylhydrazone Photoswitches.

Triarylhydrazones represent an attractive class of photochromic compounds offering many interesting features including high molar absorptivity, good addressability, and extraordinary thermal stability. In addition, unlike most other hydrazone-based photoswitches, they effectively absorb light above 365 nm. However, previously prepared triaryhydrazones suffer from low quantum yields of the Z→E photoisomerization. Here, we have designed a new subclass of naphthoyl-benzothiazole hydrazones that balance the most beneficial features of previously reported naphthoyl-quinoline and benzoyl-pyridine triarylhydrazones. These preserve the attractive absorption characteristics, exhibit higher thermal stability of the metastable form than the former and enhance the rate of the Z→E photoisomerization compared to the later, as a result of the weakening of the intramolecular hydrogen bonding between the hydrazone hydrogen and the benzothiazole moiety. Introducing the benzothiazole motif extends the tunability of the photochromic behaviour of hydrazone-based switches.

Tripodal BODIPY-Tagged and Functional Molecular Probes: Synthesis, Computational Investigations and Explorations by Multiphoton Fluorescence Lifetime Imaging Microscopy.

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).

Orthogonal Geometry Enhancing the Intersystem Crossing and Photosensitive Efficiency of Spiro Organoboron Compounds.

Based on the reported spiro organoboron compounds (PS1 and PS2 as potent 1O2 sensitizers), several new organoboron molecules (PS4-PS9) were constructed through structural modification, and their low-lying excited states and photophysical properties have been explored by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The predicted effective intersystem crossing (ISC) processes arise from the S1→T2 transition for PS4-PS6 and the S1→T4 transition for PS1, and corresponding KISC rate constants reach the order of magnitude of 109 (s-1). The organoboron compounds with a (N, N) chelate acceptor are predicted to exhibit relatively higher ISC efficiency than those bearing a (N, O) acceptor, and the planar C3NBN ring and the orthogonal configuration between the donor and acceptor moieties are responsible for the ISC rate enhancement. Importantly, the geometric features of the lowest singlet excited state (S1) for these compounds play a decisive role in their photosensitive efficiency. The present results provide a basis for better understanding of the photosensitivity of these spiro organoboron compounds and the structural modification effect.

Boosting the Efficiency of Red Thermally Activated Delayed Fluorescence via Conjugation Enhancement in Push-Pull Naphthalimide Derivatives.

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.

Plasmon induced hot carrier distribution in Ag20 -CO composite.

The interaction between plasmons and the molecules leads to the transfer of plasmon-induced hot carriers, presenting innovative opportunities for controlling chemical reactions on sub-femtosecond timescales. Through real-time time-dependent density functional theory simulations, we have investigated the enhancement of the electric field due to plasmon excitation and the subsequent generation and transfer of plasmon-induced hot carriers in a linear atomic chain of Ag20 and an Ag20 -CO composite system. By applying a Gaussian laser pulse tuned to align with the plasmon frequency, we observe a plasmon-induced transfer of hot electrons from the occupied states of Ag to the unoccupied molecular orbitals of CO. Remarkably, there is a pronounced accumulation of hot electrons and hot holes on the C and O atoms. This phenomenon arises from the electron migration from the inter-nuclear regions of the C-O bond towards the individual C and O atoms. The insights garnered from our study hold the potential to drive advancements in the development of more efficient systems for catalytic processes empowered by plasmonic interactions.

Controlling Chirogenic Effects in Porphyrin Based Supramolecular Systems: Theoretical Analysis Versus Experimental Observations.

Electronic circular dichroism (ECD) spectroscopy is a widely employed method for studying chiral analysis, requiring the presence of a chromophore close to a chiral centre. Porphyrinoids are found to be one of the best chromophoric systems serving for this purpose and enabling the application of ECD spectroscopy for chirality determination across diverse classes of organic compounds. Consequently, it is crucial to understand the induction mechanisms of ECD in the porphyrin-based complexes. The present study explores systematically the influence of secondary chromophores, bonded to an achiral zinc porphyrin or to chiral guest molecules, on the B-region of ECD spectra using the time-dependent density functional theory (TD-DFT) calculations. The study analyses the impact of change in both the conformation of achiral porphyrin (host) and change in position and conformation of chiral organic molecule (guest) on the B-band of ECD spectra (energy, intensity, sign of Cotton effect). Finally, conclusions made on model complexes are applied to published experimental data, contributing to a deeper understanding of various factors influencing ECD spectra in chiral systems. In addition, a computer program aimed to help rationalise ECD spectra by visualizing corresponding orbital energies, rotatory strengths, electric and magnetic transition moments, and angles between them, is presented.

Merocyanines form bacteriorhodopsins with strongly bathochromic absorption maxima.

There is a need to shift the absorbance of biomolecules to the optical transparency window of tissue for applications in optogenetics and photo-pharmacology. There are a few strategies to achieve the so-called red shift of the absorption maxima. Herein, a series of 11 merocyanine dyes were synthesized and employed as chromophores in place of retinal in bacteriorhodopsin (bR) to achieve a bathochromic shift of the absorption maxima relative to bR's [Formula: see text] of 568 nm. Assembly with the apoprotein bacterioopsin (bO) led to stable, covalently bound chromoproteins with strongly bathochromic absorbance bands, except for three compounds. Maximal red shifts were observed for molecules 9, 2, and 8 in bR where the [Formula: see text] was 766, 755, and 736 nm, respectively. While these three merocyanines have different end groups, they share a similar structural feature, namely, a methyl group which is located at the retinal equivalent position 13 of the polyene chain. The absorption and fluorescence data are also presented for the retinal derivatives in their aldehyde, Schiff base (SB), and protonated SB (PSB) forms in solution. According to their hemicyanine character, the PSBs and their analogue bRs exhibited fluorescence quantum yields (Φf) several orders of magnitude greater than native bR (Φf 0.02 to 0.18 versus 1.5 × 10-5 in bR) while also exhibiting much smaller Stokes shifts than bR (400 to 1000 cm-1 versus 4030 cm-1 in bR). The experimental results are complemented by quantum chemical calculations where excellent agreement between the experimental [Formula: see text] and the calculated [Formula: see text] was achieved with the second-order algebraic-diagrammatic construction [ADC(2)] method. In addition, quantum mechanics/molecular mechanics (QM/MM) calculations were employed to shed light on the origin of the bathochromic shift of merocyanine 2 in bR compared with native bR.

Solvent and alkyl substitution effects on charge-transfer mediated triplet state generation in BODIPY dyads: a combined computational and experimental study.

Donor-acceptor dyads based on BODIPYs have been recently employed to enhance the formation of triplet excited states with the process of spin-orbit charge transfer intersystem crossing (SOCT-ISC) which does not require introduction of transition metals or other heavy atoms into the molecule. In this work we compare two donor-acceptor dyads based on meso-naphthalenyl BODIPY by combining experimental and computational investigations. The photophysical and electrochemical characterization reveals a significant effect of alkylation of the BODIPY core, disfavoring the SOCT-ISC mechanism for the ethylated BODIPY dyad. This is complemented with a computational investigation carried out to rationalize the influence of ethyl substituents and solvent effects on the electronic structure and efficiency of triplet state population via charge recombination (CR) from the photoinduced electron transfer (PeT) generated charge-transfer (CT) state. Time dependent-density functional theory (TD-DFT) calculations including solvent effects and spin-orbit coupling (SOC) calculations uncover the combined role played by solvent and alkyl substitution on the lateral positions of BODIPY.

Inhibition Conversion of Aspirin into Salicylic Acid in Presence of Glycine.

Aspirin (AS) is a common drug having anti-pyretic and anti-inflammatory properties which is widely used in diverse medical conditions. The intake of AS may cause adverse effects such as gastrointestinal ulcer, tinnitus and Reye's syndrome. The adverse effects of AS arise due to conversion of AS into salicylic acid (SAL). Glycine (Gly) is a simplest non essential amino acid having anti-oxidative and anti-inflammatory effects. It also reduces the risk of obesity, hypertension, and diabetes mellitus. AS with Gly is well accepted form of the drug for the treatment of rheumatic conditions in comparisons to the bare AS. In the present work using UV-Visible absorption, fluorescence and DFT/ TD-DFT techniques confirmed that in presence of Gly inhibited the conversion of AS into SAL effectively.

Thiourea Functionalised Receptor for Selective Detection of Mercury Ions and its Application in Serum Sample.

A thiourea functionalised fluorescent probe 1-phenyl-3-(pyridin-4-yl)thiourea was synthesized and utilised as a fluorescent turn-on chemosensor for the selective recognition of Hg2+ ion over competitive metal ions including Na+, Mn2+, Li+, Cr2+, Ni2+, Ca2+, Cd2+, Mg2+, K+, Co2+, Cu2+, Zn2+, Al3+ and Fe2+ ions based on the inter-molecular charge transfer (ICT). Intriguingly, the receptor demonstrated unique sensing capabilities for Hg2+ in DMSO: H2O (10:90, v/v). The addition of Hg2+ ions to the sensor resulted in a blue shift in the absorption intensity and also enhancement in fluorescence intensity at 435 nm. Fluorescence emission intensity increased linearly with Hg2+ concentration ranging from 0 to 80 µL. The detection limit and binding constant were determined as 0.134 × 10-6 M and 1.733 × 107 M-1, respectively. The sensing behavior of Hg2+ was further examined using DLS, SEM and FTIR. The probe could detect Hg2+ ions across a wide pH range. Furthermore, the receptor L demonstrated good sensing performance for Hg2+ in bovine serum albumin and actual water samples.

Rational Design of New Small Derivatives of 2,2'-Bithiophene as Hole Transport Material for Perovskite Solar Cells.

Using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) methods, this inquiry theoretically examines seven novel hole-transport materials (HTMs) namely DFBT1, DFBT2, DFBT3, DFBT4, DFBT5, DFBT6, and DFBT7 based on the 2,2'bithiophene core for future use as HTMs for perovskite solar cells (PSCs). The model molecule has been modified through substituting the end groups situated on the diphenylamine moieties with a tow acceptor bridged by thiophene, this modification was performed to test the impact of the π-bridge and acceptor on the electronic, photophysical, and photovoltaic properties of the newly created molecules. DFBT1 - DFBT7 displayed a lower band gap (1.49 eV to 2.69 eV) than the model molecule (3.63 eV). Additionally, the newly engineered molecules presented a greater λmax ranging from 393.07 nm to 541.02 nm in dimethylformamide solvent, as compared to the model molecule (380.61 nm). The PCEs of all newly designed molecules (22.42% to 29.21%) were high compared with the reference molecule (19.62%). Thus, this study showed that all seven newly small molecules were excellent candidates for a novel PSC.

Photo-Physical Characteristics of Janus Green B in Different Solvents and its Interaction Mechanism with Silver Nanoparticles.

This work explores the effects of solvent polarity on Janus Green B (JGB) photophysical properties. The Lippert-Mataga, Billot, and Ravi equations were utilized to calculate the singlet-state excited dipole moments (µe) and ground state dipole moments (µg) using absorption and fluorescence spectra analyses. The results showed an increase in the former, which is suggestive of electronic structural alterations upon excitation. Analysis of fluorescence quantum yield values revealed that JGB's environment had an impact on its emission characteristics; it was particularly sensitive to silver nanoparticles, suggesting possible interactions. While simulations of electron density, electrostatic potential, and energy gap (Eg) helped to understand the electronic structure of JGB, theoretical absorption spectra produced by Time Dependent Density Function Theory (TD-DFT) calculations offered insights into electronic transitions during absorption. To sum up, the present study contributes to our comprehension of the molecular behavior of JGB in various solvents by elucidating the intricate relationship among solvent polarity, molecular environment, and interactions with silver nanoparticles. Additionally, theoretical computations support the interpretation of experimental results.