Novel blue-green emitting NLOphoric triphenylamine-imidazole based donor-π-acceptor compound: Solvatochromism, DFT, TD-DFT and non-linear optical studies

Augmenting the effect of solvents on optical nonlinearity by spectroscopic, DFT, solvatochromism and z-scan studies of push-pull chalcone: (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one

In this article, the structural and nonlinear optical behaviour of a chalcone derivative, (2E)-1-(4-ethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one have been studied. FT-IR, FT-Raman, and NMR spectroscopy were analyzed to validate the molecular structure. To predict the nonlinear optical characteristics of the chalcone, the DFT approach was used and the experimental results were corroborated by the computations. The bathochromic shift is obtained in linear absorbance spectra and is validated using TD-DFT. Also, the broad emission in the blue region demonstrates the blue light emission property of the sample. Using the finite-field method, the dipole moments, polarizability, first-order and second-order hyperpolarizability parameters have been computed. Ground and excited state dipole moments were quantified by solvatochromism. The third-order nonlinear optical characteristics of chalcone in polar and non-polar solvent media were examined using the open/closed-aperture z-scan technique. The chalcone displayed considerable two-photon absorption with a positive nonlinear absorption coefficient and a positive index of refraction due to the self-focussing effect. Furthermore, the optical limiting study manifests that the investigated chalcone might well be favourable for NLO applications.

A dual-state emission luminogen for lipid droplet imaging and photodynamic therapy

Organic luminogens with dual-state emission (DSE) have garnered widespread attention due to their versatility in the forms of both dilute solutions and solids. Despite the growing interest, most research on DSE focuses primarily on molecule design and photophysical investigation, with limited exploration of their practical applications. In this study, we introduce a novel fluorescent molecule, PCT, featuring a distinct D-π(A)-D' electronic structure. PCT exhibited efficient DSE properties, with high quantum yields in both dilute solutions (ΦTHF = 52.3 %) and solid-state (Φsolid = 74.6 %). Taking advantage of PCT's lipophilicity, we demonstrated its potential for targeted lipid droplet (LD) imaging in living cells and its utility in monitoring LD depletion during cellular starvation. To further enhance its applicability in photodynamic therapy (PDT), PCT was encapsulated within the amphiphilic triblock copolymer Pluronic F127, forming PCT@F127 nanoparticles with improved colloidal stability. These nanoparticles efficiently generated singlet oxygen (1O2) under white light irradiation, achieving a 1O2 quantum yield of 57.2 %. In vitro studies on MCF-7 cells revealed significant 1O2 generation and potent phototoxicity, leading to marked cell apoptosis and necrosis. These results underscore PCT's multifunctionality as a DSEgen, with promising applications in both bioimaging and PDT.

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.

Aryl-Phenanthro[9,10-d]imidazole: A Versatile Scaffold for the Design of Optical-Based Sensors

Fluorescent and colorimetric sensors are important tools for investigating the chemical compositions of different matrices, including foods, environmental samples, and water. The high sensitivity, low interference, and low detection limits of these sensors have inspired scientists to investigate this class of sensing molecules for ion and molecule detection. Several examples of fluorescent and colorimetric sensors have been described in the literature; this Review focuses particularly on phenanthro[9,10-d]imidazoles. Different strategies have been developed for obtaining phenanthro[9,10-d]imidazoles, which enable modification of their optical properties upon interaction with specific analytes. These sensing responses usually involve changes in the fluorescence intensity and/or color arising from processes like photoinduced electron transfer, intramolecular charge transfer, intramolecular proton transfer in the excited state, and Förster resonance energy transfer. In this Review, we categorized these sensors into two different groups: those bearing formyl groups and their derivatives and those based on other molecular groups. The different optical responses of phenanthro[9,10-d]imidazole-based sensors upon interaction with specific analytes are discussed.

Dynamic Coordination between a Triphenylamine-Functionalized Salicylaldehyde Schiff Base and a Copper(II) Ion

The coordination between a ligand and a metal is a spontaneous and uncontrollable process. In this Article, we successfully observe the formation of metal coordination in a triphenylamine-functionalized salicylaldehyde Schiff base with a copper(II) ion. The ligand TPA-Py first reacts with Cu²⁺ in a stepwise process to afford the dynamic complex TPA-Py@Cu²⁺ ([ligand]:[Cu²⁺] = 1:1), which further reacts with an extra copper(II) ion to afford 2TPA-Py@4Cu²⁺ with the following stepwise (or cumulative) stability constants: K₁ = 4.0694 × 10³ and K₂ = 1.0761 × 10⁶, respectively. The entire metal coordination process can be visualized, and the coordination mode of the probe toward copper was further evaluated by ultraviolet-visible/fluorescence spectra, single-crystal X-ray diffraction, density functional theory calculations, high-resolution mass spectra, and nuclear magnetic resonance spectroscopic titrations. Compound TPA-Py exhibited excellent sensitivity and specificity toward copper(II) ions in THF/water media with a low limit of detection of 2.687 × 10^-7 mol L^-1. In addition, TPI-An-Py can be applied to the detection of Cu²⁺ in real samples with satisfactory recoveries in the range of 100-112% in lake water and 98-101% in tap water. This Article not only reports an excellent fluorescence probe for copper(II) ion detection but also presents an instance for more fully understanding the metal coordination process.

Mitochondrial targeted rhodium(III) complexes: Synthesis, characterized and antitumor mechanism investigation

Recently, rhodium complexes have received intensive attentions due to their tunable chemical and biological properties as well as attractive antitumor activity. In this work, two imidazole triphenylamino rhodium complexes [Rh(ppy)₂L1]PF6 (Rh1) and [Rh(ppy)₂L2]PF6 (Rh2) (ppy = 2-phenylpyridine, L1 = 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline, L2 = N-(4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)phenyl)-4-methyl-N-(p-tolyl)aniline) have been synthesized and characterized. Both complexes display stronger anticancer activity against a various of cancer cells than cisplatin and they can effectively localize to mitochondria. Further mechanism studies show that Rh1 induce caspase-dependent apoptosis through mitochondrial damage, down-regulate the expression of B-cell lymphoma-2 (Bcl-2)/Bcl2-associated x (Bax) and reactive oxygen species (ROS) elevation. Our work provides a strategy for the construction of highly effective anticancer agents targeting mitochondrial metabolism through rational modification of rhodium complexes.

Transitioning from Intraligand π,π* to Charge-Transfer Excited States Using Thiophene-Based Donor-Acceptor Systems

A series of electron donor-acceptor compounds are reported in which both the donor and acceptor strengths are systematically altered using mono-, bi-, and terthiophene as donors and benzo[c][1,2,5]thiadiazole (btd), dipyrido[3,2-a:2',3'-c]phenazine (dppz), and the corresponding rhenium(I) complex, [ReCl(CO)₃(dppz)], as acceptors. The electronic properties of the compounds are characterized using electrochemistry, electronic absorbance and emission spectroscopies, and transient absorption spectroscopy. The effect of donor and acceptor strengths on frontier molecular orbital localization and on the charge-transfer (CT) character of optical transitions is modeled using density functional theory (DFT) calculations. The electronic absorption spectra of the compounds investigated are dominated by intraligand charge-transfer (ILCT) transitions, where the CT character is shown to increase across the series from mono- to bi- to terthiophene but not significantly across the acceptor series. Emission is shown to originate from the absorbing state. Long-lived nonemissive states have been observed using transient absorption spectroscopy and assigned using triplet-state DFT calculations, which indicate that the lowest energy excited state has more thiophene-localized π,π* character with an increasing number of appended thiophenes.

Static- and frequency-dependent NLO properties of dithienothiophene and thienothiophene bridges — A computational investigation

We have explored detailed linear and nonlinear optical properties of push-pull systems bearing thienothiophene and dithienothiophene spacers. By using density functional theory (DFT), frequency-dependent strategies were applied to examine the polarizability ([Formula: see text] and hyperpolarizability ([Formula: see text] and [Formula: see text]. The set of global and range-separated hybrid functionals with different Hartree–Fock (HF) exchange percentage at two basis sets cc-pVDZ and cc-pVTZ were used to evaluate the nonlinear optical (NLO) properties. The observed trends in the absorption maxima supported by perturbation potential analysis; as the absorption maxima increases, the respective amplitude potential decreases. For the investigated compounds, [Formula: see text]-conjugation along with the type of substituted acceptor plays a crucial role in the enhancement of NLO properties. The presence of acceptor group and length of conjugation increase between the D and A group; the first- and second-order intrinsic hyperpolarizability increases, leads to enhanced first- as well as second-order hyperpolarizability. Bond length alternation (BLA)/bond order alteration (BOA) exploration suggested that compounds attain cyanine limit. The trends in NLO properties for investigated compounds are supported by chemical reactivity descriptors, hardness and hyperhardness analysis. The polarizability is linearly correlated with the hyperpolarizability parameters ([Formula: see text] and [Formula: see text] and shows a good regression coefficient by figures of merit analysis.