Aromatic Ring Research Articles

Comprehensive Experimental and Computational Analysis of the Structural and HSA Binding Properties of Newly Synthesized Coumarin-Trimethoxybenzohydrazide Derivative

Polycyclic aromatic compounds encompass a diverse array of molecules that exhibit remarkable chemical activity and play pivotal roles across various scientific domains. Coumarins represent a diverse class of heterocyclic compounds, which exhibit a wide range of significant biological and pharmacological activities, while containing at least two aromatic rings in their structure. Because chemical, biological, as well as pharmacological properties and activities are highly dependent on the structural characteristics of the molecule, in this paper a detailed structural investigation of the monocrystal structure of newly synthesized (E)-N′-(1-(2,4-dioxochroman-3-ylidene)ethyl)-3,4,5-trimethoxybenzohydrazide was performed. The DFT model that is best suited for describing the structural parameters of coumarin-benzohydrazides was determined. Out of three tested models which were previously proven to be excellent in describing structures of organic compounds, B3LYP-D3BJ was found to be the best in describing the structure of investigated coumarin derivative in regard to the obtained X-ray and spectroscopic data. Determination of the best theoretical model allows for better structural characterization of the coumarin-benzohydrazides for which monocrystals and consequently X-ray structure cannot be obtained. Finally, both experimental and computational analysis indicated (with high mutual correlation) that investigated compound showed excellent binding potential toward the albumin, indicating good distribution through the organism.

Late-Stage Saturation of Drug Molecules.

The available methods of chemical synthesis have arguably contributed to the prevalence of aromatic rings, such as benzene, toluene, xylene, or pyridine, in modern pharmaceuticals. Many such sp2-carbon-rich fragments are now easy to synthesize using high-quality cross-coupling reactions that click together an ever-expanding menu of commercially available building blocks, but the products are flat and lipophilic, decreasing their odds of becoming marketed drugs. Converting flat aromatic molecules into saturated analogues with a higher fraction of sp3 carbons could improve their medicinal properties and facilitate the invention of safe, efficacious, metabolically stable, and soluble medicines. In this study, we show that aromatic and heteroaromatic drugs can be readily saturated under exceptionally mild rhodium-catalyzed hydrogenation, acid-mediated reduction, or photocatalyzed-hydrogenation conditions, converting sp2 carbon atoms into sp3 carbon atoms and leading to saturated molecules with improved medicinal properties. These methods are productive in diverse pockets of chemical space, producing complex saturated pharmaceuticals bearing a variety of functional groups and three-dimensional architectures. The rhodium-catalyzed method tolerates traces of dimethyl sulfoxide (DMSO) or water, meaning that pharmaceutical compound collections, which are typically stored in wet DMSO, can finally be reformatted for use as substrates for chemical synthesis. This latter application is demonstrated through the late-stage saturation (LSS) of 768 complex and densely functionalized small-molecule drugs.

Tribological properties of polyaromatic organics as lubricating grease

The tribological properties of polyaromatic organics (xPyE) as lubricating grease additives are studied by simulations and experiments. Molecular Dynamics (MD) simulations are used to simulate the mechanical properties of four kinds of polyaromatic organics (2P1E, 3P2E, 4P3E, and 5P4E) with different aromatic ring numbers and a mass fraction under 300 MPa and 5 m/s relative shear velocity of the two solid walls. The friction force, positive pressure, stress, and adsorption energy are calculated quantitatively. Meantime, the friction coefficient of lubricating grease and the wear morphology of the sample are measured by Multifunctional Friction and Wear Testing Machine. The results show that the organic additives adsorbed on the wall form a protective film during the shearing process, improving the bearing capacity and reducing friction and wear. Among them, the 3P2E organic additive has an appropriate number of aromatic rings. Its single molecular adsorption energy and unit adsorption energy are higher than other organic additives and can uniformly lay on the wall to form a stable, protective film. This demonstrates the best friction performance and improves the load-bearing capacity of the lubricating film, reducing maximum wall stress by 53.4 %.

Predisposition in Dynamic Covalent Chemistry: The Role of Non-Covalent Interactions in the Assembly of Tetrahedral Boronate Cages.

Directional bonding strategies guide the design of complex molecular architectures, yet challenges arise due to emergent behavior. Rigid structures face geometric constraints and sensitivity to mismatches, hindering the efficient assembly of molecular organic cages (MOCs). Harnessing intramolecular non-covalent interactions offers a promising solution, broadening geometrical possibilities and enhancing adaptability to boost assembly yields. However, identifying these interactions remains challenging, with their full potential sometimes latent until final assembly. This study explores these challenges by synthesizing boronic acid tripods with varied oxygen positions at the tripodal feet and investigating their role in assembling tetrahedral boronate MOCs. Our results reveal substantial differences in the assembly efficiency among tripods. While the building blocks with oxygen in the benzylic position relative to the central aromatic ring form the MOCs in high yields, those with the oxygen atom directly bound to the central aromatic ring, only yield traces. Through X-ray crystallography and DFT analyses, we elucidate how intramolecular interactions profoundly influence the geometry of the building blocks and cages in a relay-like fashion, highlighting the importance of considering intramolecular interactions in the rational design of (supra)molecular architectures.

How Do Molecular Tweezers Bind to Proteins? Lessons from X-ray Crystallography.

To understand the biological relevance and mode of action of artificial protein ligands, crystal structures with their protein targets are essential. Here, we describe and investigate all known crystal structures that contain a so-called "molecular tweezer" or one of its derivatives with an attached natural ligand on the respective target protein. The aromatic ring system of these compounds is able to include lysine and arginine side chains, supported by one or two phosphate groups that are attached to the half-moon-shaped molecule. Due to their marked preference for basic amino acids and the fully reversible binding mode, molecular tweezers are able to counteract pathologic protein aggregation and are currently being developed as disease-modifying therapies against neurodegenerative diseases such as Alzheimer's and Parkinson's disease. We analyzed the corresponding crystal structures with 14-3-3 proteins in complex with mono- and diphosphate tweezers. Furthermore, we solved crystal structures of two different tweezer variants in complex with the enzyme Δ1-Pyrroline-5-carboxyl-dehydrogenase (P5CDH) and found that the tweezers are bound to a lysine and methionine side chain, respectively. The different binding modes and their implications for affinity and specificity are discussed, as well as the general problems in crystallizing protein complexes with artificial ligands.

Tuning Green Explosives through SNAr Chemistry.

Reactivity and regioselectivity of SNAr-type fluorine substitution with azide in polyfluorosubstituted nitrobenzenes was studied both theoretically and experimentally. The obtained polyazido-substituted nitrobenzene derivatives were extensively characterized by NMR, IR, HPLC, X-ray, and DFT methods. It was found that the substitution with the azide nucleophile occurs first at the para- and the ortho-positions to the NO2-group and that transazidation reactions also occur here. Thermal decomposition of prepared azidonitrobenzenes was studied both in controlled (kinetic decay) and uncontrolled (explosion) modes. In case of the controlled thermal decomposition of ortho-azidonitrobenzenes, benzofuroxans were found as major products of the reaction unless another azido group was adjacent to the furoxan moiety. The bursting power of azidonitrobenzenes was found to rise gradually with the number of the azide substituents in the aromatic ring.

Dual Antitubercular and Antileishmanial Profiles of Quinoxaline Di-N-Oxides Containing an Amino Acidic Side Chain.

We present a new category of quinoxaline di-N-oxides (QdNOs) containing amino acid side chains with dual antituberculosis and antileishmanial activity. These compounds were synthesized by combining a regioselective 2,5-piperazinedione opening and a Beirut reaction and were screened for their activity against Mycobacterium tuberculosis and the promastigote and amastigote forms of representative species of the Leishmania genus. Most QdNOs exhibited promising antitubercular activity with IC50 values ranging from 4.28 to 49.95 μM, comparable to clinically established drugs. Structure-activity relationship analysis emphasized the importance of substituents on the aromatic ring and the side chain. Antileishmanial tests showed that some selected compounds exhibited activity comparable to the positive control miltefosine against promastigotes of Leishmania amazonensis and Leishmania donovani. Notably, some compounds were found to be also more potent and less toxic than miltefosine in intracellular amastigote assays against Leishmania amazonensis. The compound showing the best dual antitubercular and leishmanicidal profile and a good selectivity index, 4h, can be regarded as a hit compound that opens up new opportunities for the development of integrated therapies against co-infections.

Ligand‐Free Copper(0)‐Catalyzed C−S Ullmann‐Type Cross‐Coupling Reaction: S‐Arylation of 5,4‐Disubstituted 2,4‐Dihydro‐3H‐1,2,4‐triazole‐3‐thiones

AbstractWe investigated the S‐arylation of 5,4‐disubstituted 2,4‐dihydro‐3H‐1,2,4‐triazole‐3‐thiones under ligand‐free Cu(0) catalysis employing Ullmann‐type reaction conditions. We determined optimal reaction conditions and assessed the impact of substituents in the arylating agent on the reaction progress. Notably, the presence of an electron‐withdrawing group (EWG) in the aryl halide facilitated the reaction even without a catalyst. In particular, an EWG in the para position of the aromatic ring exerted a directing effect on the leaving group, regardless of the halogen present.

Tuning the structure of pendant groups in poly(α‐arylTMC)s: A pathway to high glass transition temperature

AbstractAliphatic polycarbonates have been explored as environmentally benign alternatives to aromatic polycarbonates. Improvements to the glass transition temperature (Tg) of aliphatic polycarbonates have been pursued by several groups. We recently showed that attaching a pendant aromatic group to poly(TMC) can enhance the Tg. Also, we have shown that para substituents on the pendant group have an impact on the Tg. Here, we have explored the role of bulky pendant groups and the effect of substituent position on the pendant aromatic ring. We prepared novel naphthalene‐derived poly(TMC)s as well as 2‐Br‐substituted poly(PhTMC). The 2‐bromophenyl derivative showed a Tg of 69.5 °C which represents a nominal increase in comparison to the 4‐bromo derivative that we reported earlier. This suggests that the position of the substituent does not have a critical impact on Tg. With naphthalene derivatives, the increase in steric bulk led to an increase in Tg. Increase of chain length beyond fifty monomer units had a minimal impact on Tg. Finally, when 4‐bromonaphthyl moiety was the pendant group, we observed a Tg of 97 °C. This demonstrates that Tg can be varied significantly by modifying the pendant groups. We have also shown that the 1,3‐diols used in our polymer are non‐cytotoxic.

Theoretical analysis of hydrogen solubility in direct coal liquefaction solvents

The cyclic hydrogenation technology in a direct coal liquefaction process relies on the dissolved hydrogen of the solvent or oil participating in the hydrogenation reaction. Thus, a theoretical basis for process optimization and reactor design can be established by analyzing the solubility of hydrogen in liquefaction solvents. Experimental studies of hydrogen solubility in liquefaction solvents are challenging due to harsh reaction conditions and complex solvent compositions. In this study, the composition and content of liquefied solvents were analyzed. As model compounds, hexadecane, toluene, naphthalene, tetrahydronaphthalene, and phenanthrene were chosen to represent the liquefied solvents in chain alkanes and monocyclic, bicyclic, and tricyclic aromatic hydrocarbons. The solubility of hydrogen X (mol/mol) in pure solvent components and mixed solvents (alkanes and aromatics mixed in proportion to the chain alkanes + bicyclic aromatic hydrocarbons, bicyclic saturated aromatic hydrocarbons + bicyclic aromatic hydrocarbons, and bicyclic aromatic hydrocarbons + compounds containing heteroatoms composed of mixed components) are determined using Aspen simulation at temperature and pressure conditions of 373–523 K and 2–10 MPa. The results demonstrated that at high temperatures and pressures, the solubility of hydrogen in the solvent increases with the increase in temperature and pressure, with the pressure having a greater impact. Furthermore, the results revealed that hydrogen is more soluble in straight-chain alkanes than in other solvents, and the solubility of eicosanoids reaches a maximum of 0.296. The hydrogen solubility in aromatic ring compounds decreased gradually with an increase in the aromatic ring number. The influence of chain alkanes on the solubility of hydrogen predominates in a mixture of solvents with different mixing ratios of chain alkanes and aromatic hydrocarbons. The solubility of hydrogen in mixed aromatic solvents is less than that in the corresponding single solvents. Hydrogen is less soluble in solvent compounds containing heteroatoms than in compounds without heteroatoms.

Photochemistry of micro-solvated benzonitrile complexes with water/ammonia bordering on the formation of icy grains

Polycyclic aromatic hydrocarbons (PAHs) act as condensation nuclei for water/ammonia molecules forming icy water clusters. In the context of small aromatic rings, we have theoretically examined complexes of benzonitrile with water/ammonia molecules in order to investigate the photochemical kinetics of the icy grain formation. First, we obtain the structure of energetically stable complexes containing different H-bonding patterns and analyze their effects in the infrared (IR) and vacuum ultraviolet (VUV) spectra, before and after ionization. Second, we evaluate the H-bonding reorientation kinetics of the complexes at low temperatures, which indicates that the process involving water occurs faster than the corresponding process involving ammonia. Finally, the thermal rate constants indicate which configurations are the most likely to be ionized under vacuum ultraviolet (VUV) irradiation. Our results are consistent with what has experimentally been observed for related complexes, and are useful as a starting point to investigate the process of the icy grains formation. This study provides insight into possible subsequent photochemical reactions occurring in the interstellar medium (ISM) or in jet-cooled molecular complexes.

Effect of ionic liquid-surfactant compound solutions on the wettability and functional groups of coal

In order to investigate the feasibility of ionic liquid-surfactant compound solutions for coal dust suppression, three ionic liquids and sodium alpha-olefin sulfonate (AOS) were selected to be compounded respectively. The compound solutions were optimized by surface tension tests and coal dust settling experiments, and FTIR and SEM tests were carried out on coal samples treated with the optimum wetting agent. The results show that when the concentration is 0.3 wt%, and the ratio of [Bmim][Cl]/AOS is 4:6, the wetting rate of compound solution is the maximum. The content of hydrophilic functional groups OH…O and C-O in the coal samples increases significantly, and the degree of benzene ring substitutions is elevated; while hydrophobic functional groups –CH, aromatic ring C = C, and benzene ring 3 substitutions (3H) are destroyed by dissolution. The micromorphology of the coal surface changes with the appearance of many cracks and pores and an increase in surface roughness. [Bmim]+ can adsorb on the drain absorption points on the coal surface by electrostatic effect, turning them into water absorption sites and attracting the surrounding AOS molecules to arrange the composite adsorption layer more closely. These results can contribute to the development of novel wetting agents with specific structures and provide theoretical guidance for the reduction of coal dust concentrations.

Unveiling intermolecular mechanism and electronic properties between asphaltene and deep eutectic solvent for enhanced oil recovery using first principles calculation

Electronic structure and interaction energy calculations offer critical insights into non-bonded interactions in solute–solvent systems that can be used to extract heavy oil, particularly asphaltene, in enhanced oil recovery. The present study examines deep eutectic solvent (DES) interaction with asphaltene through first-principles calculations, revealing the role of hydrogen bonds, overall system stability, and its mechanism. The analysis reveals that the inclusion of asphaltene makes the DES-asphaltene structure less stable, i.e., increasing wettability with DES. DES formed non-bonded interactions with asphaltene's aliphatic segments but excluded aromatic rings due to strong π-π interactions. Among the studied DESs, DES1 (choline chloride and urea, 1:2 ratio) exhibited a strong interaction with asphaltene (-103.946 kJ/mol) and formed a hydrogen bond. All systems show negative binding energies, which indicate stability. Notably among them, DES2 (choline chloride and thiourea, 1:2) and DES3 (choline chloride and ethylene glycol, 1:2) displayed remarkable stability with asphaltene, evident in a widened band gap of 2.182 and 2.157 eV, respectively.

Shaping sustainable pathways: Enhancing mechanical properties of biocomposite through tannic acid treatment of flax fabrics

Biocomposites developed using natural fibers serve as a sustainable alternative to synthetic composite materials. However, narrowing the performance gap between synthetic composites and biocomposites requires serious efforts. A promising approach is the modification of natural fibers using various chemical treatments. This paper investigates the potential of tannic acid (TA) treatment as a sustainable approach to enhance mechanical performance and reduce moisture absorption of flax fabric-reinforced biocomposites. The methodology involves the treatment of flax woven fabric with tannic acid, a naturally occurring polyphenolic compound, followed by the fabrication of biocomposite using a green epoxy matrix. The variables studied during treatment are TA concentration and processing time. Characterization of untreated and treated flax fabric and its composites was done using various analytical techniques such as FTIR spectroscopy, moisture absorption and mechanical testing (tensile strength, flexural strength, and impact resistance). FTIR spectroscopy of TA-treated flax confirmed attachment of aromatic rings and carbon double bond formation, thus serving for properties enhancement. The mechanical characterization of composites showed that properties are enhanced up to an optimum limit of concentration and processing time i.e., 1 % concentration and 30 min of processing. Moisture absorption of the TA-treated composite also reduced significantly as compared to untreated composites. These findings contribute towards the advancement in sustainable biocomposites and pave the way for their utilization in various applications.

Difluoroboron Complexes Based on Benzimidazole-Phenolates as Blue Emitters.

Novel four-coordinated boron complexes (1-5) were synthesized via a reaction between BF3·CH3OH and benzimidazole-phenolate ligands (L1-L5), which are N,O-donors. These complexes exhibit intense blue emission in the solution and solid states accompanied by notable fluorescence quantum yields (ΦF). The study of the structure-property relation, through theoretical and experimental approaches, revealed a distinctive trend where compounds incorporating electron-donating substituents (methyl and ethoxy groups) in the phenolate moiety manifest shifts in emission wavelengths across the blue spectrum, concomitant with an increase in ΦF. Furthermore, the incorporation of an aromatic ring into the benzimidazole moiety considerably intensifies the rate of radiative relaxation from excited states. Notably, in the solid phase, either as a crystalline powder or loaded into polymer films, these modified complexes maintain or even surpass ΦF values observed in molecular solutions, ranging from 0.18 to 0.57, depending on the substitution. This characteristic makes these compounds attractive for applications in optoelectronics. All of the compounds were characterized using 1H, 13C, 11B, and 19F NMR, elemental analysis, and the molecular structures were corroborated through single-crystal X-ray diffraction analysis. Computational calculations via time-dependent density functional theory further elucidate the tunability of optical bandgaps through group substitution on ligands, aligning well with experimental observations.

Non-target analysis of crude oil photooxidation products at high latitudes and their biological effects

With new oil and gas lease sales in high-latitude regions, there exists a need to better understand the chemical fate of spilled oil and its effects on biological life. To address this need, laboratory simulations of crude oil spills under sub-Arctic conditions were conducted using artificial seawater and exposure to solar irradiation to create Hydrocarbon Oxidation Products (HOPs). HOPs characterization and their biological effects were assessed using ultra high-performance liquid chromatography (UHPLC) with high resolution mass Orbitrap spectrometry and the aryl hydrocarbon receptor (AhR) chemically activated luciferase gene expression (CALUX) assay. Non-target UHPLC-Orbitrap mass spectrometry analysis identified 251 HOPs that were in greater abundance in light-exposed samples than dark controls. Oxidized polycyclic aromatic hydrocarbons were also detected, including phenanthrene quinone, anthraquinone, hydroxyanthraquinone, and 9-fluoreneone. The composition of HOPs were consistent with photo-products of alkylated two to four ring PAHs, primarily compounds between 1 and 3 aromatic rings and 1–3 oxygens. The HOP mixture formed during photochemical weathering of Cook Inlet crude oil induced greater AhR activity than parent petroleum products solubilized in dark controls, indicating that HOPs, as a complex mixture, may contribute to petroleum toxicity more than the parent petroleum compounds. These non-targeted approaches provide the most comprehensive analysis of hydrocarbon oxidation products to date, highlighting the diversity of the complex mixture resulting from the photooxidation of crude oil and the limitations of targeted analyses for adequately monitoring HOPs in the environment. Taken together, these data identify a critical “blind spot” in environmental monitoring and spill clean-up strategies as there is a diverse pool of HOPs that may negatively impact human and ecosystem health.

Theoretical investigation on graphene induced self-alignment of donor-acceptor structures

Non-covalent functionalization of graphene (Gr) with conducting polymers (CPs) improves the electrical and mechanical properties of both materials owing to the noncovalent π-π stacking interaction between the surface and the aromatic rings in CPs. However, a comprehensive understanding of the self-organization and chain orientation of CPs on the Gr surface remains lacking, which may limit the engineering of CP-Gr complexes with optimized morphology for optoelectronic applications. This study focuses on the Density Functional Theory (DFT) calculations and homemade Python programming code to investigate the self-organization of donor (D)-acceptor (A) type molecules on the Gr surface, aiming to elucidate factors governing the direction of self-alignment. Specifically, basic structural parameters characterizing the aromatic D-A molecules, such as the intramolecular aromatic ring distances, are explored to determine the rules for the preferred alignment direction of the CP monomers on the Gr surface, either in armchair or zigzag paths. Additionally, the influence of Gr on the morphological properties of aromatic molecules, variations in interaction energies between Gr and D-A-D systems with changing A units, and the impact of Gr size on molecular fitting characteristics are examined. The accurate determination of chain alignment direction, which can be applied for all conjugated small molecules and polymers at 2D material interfaces is crucial for guiding experimental studies aimed at tailoring structures and enhanced properties, such as promoting the crystalline domains with high electrical conductivity.

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Developing Green Sorbents Derived from Natural Materials for Microextraction and Determination of Emerging Contaminants

Numerical study on the temperature dependence of soot formation in acetylene pyrolysis blended with methane, formaldehyde, methanol, and dimethyl ether

Abstract This paper addresses the combined effects of varying C/H and C/O ratios as well as of the molecular structure of the fuels selected on the normalized soot volume fraction f V. For the simulations, an already existing and validated reaction mechanism for the pyrolysis of C2H2 in argon, Aghsaee et al. (Combust. Flame 2014, 161, 2263–2269), was used in the current work. It was extended with PAH reactions from coronene (C24H12) up to ovalene (C32H14), whereas general principles for the rapid build-up of large PAHs were presented. Soot formation was modeled according to Appel et al. (Combust. Flame 2000, 121, 122–136) by applying the method of moments. A validation of the extended reaction model was carried out for shock-wave-induced O2/C2H2 mixtures from literature. In the following, the influence of blends of methane (CH4), formaldehyde (CH2O), methanol (CH3OH), and dimethyl ether (CH3)2O on soot formation during C2H2 pyrolysis diluted in Ar was studied. Special emphasis was laid on the inception chemistry of soot formation. The role of intermediates, such as the propargyl radical (C3H3), leading towards benzene and polyaromatic hydrocarbon (PAH) formation and their interplay with hydrogen molecules (H2) to H atoms (H) ratio was examined. All blends increased the ratio of the concentrations of H2 and H leading thus to reduced soot inception and soot formation. However, soot suppressing effects were overrun by supporting ones when the additives provided suitable molecular groups, such as methyl radicals (CH3), in sufficient high concentrations for early aromatic ring formation. Thus, a prominent synergistic effect on soot formation was found for the CH4/C2H2 mixture only. Besides, species able to mirror characteristics of the soot formation process, such as the peak value of the normalized soot volume fraction, are presented. The findings of this work indicate the synergistic effect of H2/H and C/O ratios as well as of methyl radicals on the PAHs’ production of appropriate size able to initiate soot inception process in an aliphatic fuel.

Absorption spectra of p-nitroaniline derivatives: charge transfer effects and the role of substituents.

Push-pull compounds are model systems and have numerous applications. By changing their substituents, properties are modified and new molecules for different applications can be designed. The work investigates the gas-phase electronic absorption spectra of 15 derivatives of push-pull para-nitroaniline (pNA). This molecule has applications in pharmaceuticals, azo dyes, corrosion inhibitors, and optoelectronics. Both electron-donor and electron-withdrawing groups were investigated. Employing machine learning-derived Hammett's constants σm, σm0, σR, and σI, correlations between substituents and electronic properties were obtained. Overall, the σm0 constants presented the best correlation with HOMO and LUMO energies, whereas the σR constants best agreed with the transition energy of the first band and HOMO-LUMO energy gap. Electron-donors, which have lower σR values, redshift the absorption spectrum and reduce the HOMO-LUMO energy gap. Conversely, electron-withdrawing groups (higher σR's) blueshift the spectrum and increase the energy gap. The second band maximum energies, studied here for the first time, showed no correlation with σ but tended to increase with σ. A comprehensive charge transfer (CT) analysis of the main transition of all systems was also carried out. We found that donors (lower σ's) slightly enhance the CT character of the unsubstituted pNA, whereas acceptors (higher σ's) decrease it, leading to increased local excitations within the aromatic ring. The overall CT variation is not large, except for pNA-SO2H, which considerably decreases the total CT value. We found that the strong electron donors pNA-OH, pNA-OCH3, and pNA-NH2, which have the smallest HOMO-LUMO energy gaps and lowest σ's, have potential for optoelectronic applications. The results show that none of the studied molecules is fluorescent in the gas phase. However, pNA-NH2 and pNA-COOH in cyclohexane and water reveal fluorescence upon solvation. We investigated theoretically employing the second-order algebraic diagrammatic construction (ADC(2)) ab initio wave function and time-dependent density functional theory (TDDFT) the gas-phase electronic absorption spectra of 15 derivatives of p-nitroaniline (pNA). The investigated substituents include both electron-donor (C6H5, CCH, CH3, NH2, OCH3, and OH,) and electron-withdrawing (Br, CCl3, CF3, Cl, CN, COOH, F, NO2, and SO2H) substituents.