Extended Quinolizinium-Fused Corannulene Derivatives: Synthesis and Properties

Reported here is the design and synthesis of a novel class of extended quinolizinium-fused corannulene derivatives with curved geometry. These intriguing molecules were synthesized through a rationally designed synthetic strategy, utilizing double Skraup-Doebner-Von Miller quinoline synthesis and a rhodium-catalyzed C-H activation/annulation (CHAA) as the key steps. Single-crystal X-ray analysis revealed a bowl depth of 1.28-1.50 Å and a unique "windmill-like" shape packing of 12a(2PF6-) due to the curvature and incorporation of two aminium ions. All of the newly reported curved salts exhibit green to orange fluorescence with enhanced quantum yields (Φf = 9-13%) and improved dispersibility compared to the pristine corannulene (Φf = 1%). The reduced optical energy gap and lower energy frontier orbital found by doping extended corannulene systems with nitrogen cations was investigated by UV-vis, fluorescence, and theoretical calculations. Electrochemical measurements reveal a greater electron-accepting behavior compared with that of their pyridine analogues. The successful synthesis, isolation, and evaluation of these curved salts provide a fresh perspective and opportunity for the design of cationic nitrogen-doped curved aromatic hydrocarbon-based materials.

Bromopyrene Symphony: Synthesis and Characterisation of Isomeric Derivatives at Non-K Region and Nodal Positions for Diverse Functionalisation Strategies

Pyrene, a renowned aromatic hydrocarbon, continues to captivate researchers due to its versatile properties and potential applications across various scientific domains. Among its derivatives, bromopyrenes stand out for their significance in synthetic chemistry, materials science, and environmental studies. The strategic functionalisation of pyrene at non-K region and nodal positions is crucial for expanding its utility, allowing for diverse functionalisation strategies. Bromo-substituted precursors serve as vital intermediates in synthetic routes; however, the substitution pattern of bromoderivatives significantly impacts their subsequent functionalisation and properties, posing challenges in synthesis and purification. Understanding the distinct electronic structure of pyrene is pivotal, dictating the preferential electrophilic aromatic substitution reactions at specific positions. Despite the wealth of literature, contradictions and complexities persist in synthesising suitably substituted bromopyrenes due to the unpredictable nature of substitution reactions. Building upon historical precedents, this study provides a comprehensive overview of bromine introduction in pyrene derivatives, offering optimised synthesis conditions based on laboratory research. Specifically, the synthesis of mono-, di-, tri-, and tetrabromopyrene isomers at non-K positions (1-, 3-, 6-, 8-) and nodal positions (2-, 7-) is systematically explored. By elucidating efficient synthetic methodologies and reaction conditions, this research contributes to advancing the synthesis and functionalisation strategies of pyrene derivatives, unlocking new possibilities for their utilisation in various fields.

Pyrene-Functionalized Fluorescent Nanojars: Synthesis, Mass Spectrometric, and Photophysical Studies

Nanojars are a class of supramolecular coordination complexes based on pyrazolate, Cu2+, and OH- ions that self-assemble around highly hydrophilic anions and serve as efficient anion binding and extraction agents. In this work, the synthesis, characterization, and photophysical properties of pyrene-functionalized fluorescent nanojars are presented. Three pyrene derivatives, 4-(pyren-1-yl)pyrazole (HL1), 4-(5-(pyren-1-yl)pent-4-yn-1-yl)pyrazole (HL2), and 4-(3-(pyrazol-4-yl)propyl)-1-(pyren-1-yl)-1,2,3-triazole (HL3), and the corresponding nanojars were synthesized and characterized using nuclear magnetic resonance spectroscopy and mass spectrometry. Electronic absorption, steady-state, and time-resolved fluorescence measurements were carried out to understand the interaction between the pyrene fluorophore and copper nanojars. Optical absorption measurements have shown minor ground state interaction between the fluorophore and nanojars. The fluorescence of pyrene is significantly quenched when attached to nanojars, suggesting strong contribution from the paramagnetic Cu2+ ions. Significant static quenching is observed in the case of L1, when pyrene is directly bound to the nanojar, whereas in the case of L2 and L3, when pyrene is attached to the nanojars using flexible tethers, both static and dynamic quenching are observed.

Five-Fold Symmetric Pentaindolo- and Pentakis(benzoindolo)Corannulenes: Unique Structural Dynamics Derived from the Combination of Helical and Bowl Inversions

Peripherally π-extended corannulenes bearing quintuple azahelicene units, 10 and 11, were prepared and their dynamic behaviors were studied experimentally and theoretically. The fused corannulenes were synthesized from sym-pentabromocorannulene in three steps. X-Ray diffraction analysis for 10 displayed a conformer possessing a P(M) bowl chirality and a PPMPM (PMPMM) helical chirality, which was found to be the most stable conformer(s). Variable-temperature NMR measurements of 10 and 11 revealed that their structural isomers can be interconvertible in solution, depending on the steric congestion around the helical scaffolds. Automated search for conformers in the equilibrium and transition states by Artificial Force Induced Reaction (AFIR) method revealed their interconversion networks, including bowl-inversion and helical-inversion. This analysis indicated that the co-existing corannulene and azahelicene moieties influence the conformational dynamics, which leads to mitigation of the activation energy barriers for isomerization.

Fluorescent Chromophores Containing the Nitro Group: Relatively Unexplored Emissive Properties

Apart from numerous applications, for example in azo dye precursors, explosives, and industrial processes, the nitro group (-NO₂ ) appears on countless molecules in photochemical research owing to its unique characteristics such as a strong electron-withdrawing ability and facile conversion to the reduced substituent. Although it is well known as a fluorescence quencher, fluorescent chromophores that contain the nitro group have also emerged, with 3-nitrophenothiazine being recently reported to have 100 % emission quantum yield in nonpolar solvents. The diverse characters of nitro-containing chromophores motivated us to systematically review those chromophores with nitro substituents, their associated photophysical properties, and applications. In this Review, we succinctly elaborate the advance of the fluorescent nitro chromophores in fields of intramolecular charge transfer, fluorescent probes and nonlinear properties. Special attention is paid to the rationalization of the associated emission spectroscopy, so that the readers can gain insights into the structure-photophysics relationship and hence gain insights for the strategic design of nitro chromophores.

Electron-Rich π-Extended Diindolotriazatruxene-Based Chemosensors with Highly Selective and Rapid Responses to Nitroaromatic Explosives

A series of electron-rich π-extended diindolotriazatruxene-based compounds DIT, 4Py-DIT (bearing pyrene units) and 4PyF-DIT (bearing fluorene units) have been explored and investigated as fluorescence chemosensors. Quantitative analysis through fluorescence titrations showed that the resulting DIT molecules exhibited highly selective response to electron-deficient nitroaromatic explosives. The calculated Stern-Volmer quenching constants (>4.0×10³  M^-1 ) revealed that these sensors were much more sensitive in solution compared to most of the existing small-molecule fluorescence chemosensors based on pyrene, triphenylene, triphenylamine, and triazatruxene skeletons. Fluorescence quenching showed that the sensors adsorbed on paper were sensitive to explosives in the solid, solution, and vapor phases, with fast response times of about 10 s. Moreover, these chemosensors are reusable for the detection of nitroaromatic compounds as they recover their fluorescence intensity after quenching.

Synthesis and optical properties of mono- and diaminocorannulenes

A simple synthesis of aminocorannulenes leads to the discovery of surprising properties: tunable visible emission; solid-state fluorescence; water-soluble fluorescent corannulenes.

Unravelling the photophysics of triphenylamine and diphenylamine dyes: a comprehensive investigation with ortho-, meta- and para-amido substituted derivatives

This study reveals the intriguing solvent polarity dependent modulations in the photophysics of triphenylamine and diphenylamine based dyes.

Constitutional isomers of dendrimer-like pyrene substituted cyclotriphosphazenes: synthesis, theoretical calculations, and use as fluorescence receptors for the detection of explosive nitroaromatics

Two constitutionally isomeric bis-pyrenyl phenol dendrons (4 and 6) and their dendrimer-like cyclotriphosphazene derivatives (5 and 7) are designed, synthesized and fluorescence detection behaviors are evaluated for nitro aromatic compounds (NACs).

Real-time fluorescence quenching-based detection of nitro-containing explosive vapours: what are the key processes?

The detection of explosives continues to be a pressing global challenge with many potential technologies being pursued by the scientific research community. Luminescence-based detection of explosive vapours with an organic semiconductor has attracted much interest because of its potential for detectors that have high sensitivity, compact form factor, simple operation and low-cost. Despite the abundance of literature on novel sensor materials systems there are relatively few mechanistic studies targeted towards vapour-based sensing. In this Perspective, we will review the progress that has been made in understanding the processes that control the real-time luminescence quenching of thin films by analyte vapours. These are the non-radiative quenching process by which the sensor exciton decays, the analyte-sensor intermolecular binding interaction, and the diffusion process for the analyte vapours in the film. We comment on the contributions of each of these processes towards the sensing response and, in particular, the relative roles of analyte diffusion and exciton diffusion. While the latter has been historically judged to be one of, if not the primary, causes for the high sensitivity of many conjugated polymers to nitrated vapours, recent evidence suggests that long exciton diffusion lengths are unnecessary. The implications of these results on the development of sensor materials for real-time detection are discussed.

Corannulene: a molecular bowl of carbon with multifaceted properties and diverse applications

The chemistry, properties and applications of corannulene are discussed.

A 1,2,3-triazolyl based conjugated microporous polymer for sensitive detection of p-nitroaniline and Au nanoparticle immobilization

A 1,2,3-triazolyl based fluorescent CMP was used as an excellent chemosensor for p-nitroaniline detection and a support for Au catalyst deposition.

Proton triggered emission and selective sensing of 2,4,6-trinitrophenol using a fluorescent hydrosol of 2-phenylquinoline

Compound 2-phenylquinoline (PhQ) displayed novel aggregation induced emission enhancement (AIEE) characteristics in its aggregate/solid state. It allows reversible fluorescence switching in acidic and basic media and ‘turn off’ fluorescence sensor for TNP.

Hierarchical Corannulene-Based Materials: Energy Transfer and Solid-State Photophysics

We report the first example of a donor-acceptor corannulene-containing hybrid material with rapid ligand-to-ligand energy transfer (ET). Additionally, we provide the first time-resolved photoluminescence (PL) data for any corannulene-based compounds in the solid state. Comprehensive analysis of PL data in combination with theoretical calculations of donor-acceptor exciton coupling was employed to estimate ET rate and efficiency in the prepared material. The ligand-to-ligand ET rate calculated using two models is comparable with that observed in fullerene-containing materials, which are generally considered for molecular electronics development. Thus, the presented studies not only demonstrate the possibility of merging the intrinsic properties of π-bowls, specifically corannulene derivatives, with the versatility of crystalline hybrid scaffolds, but could also foreshadow the engineering of a novel class of hierarchical corannulene-based hybrid materials for optoelectronic devices.

Redox-State Dependent Spectroscopic Properties of Porous Organic Polymers Containing Furan, Thiophene, and Selenophene

A series of electroactive triarylamine porous organic polymers (POPs) with furan, thiophene, and selenophene (POP-O, POP-S, and POP-Se) linkers have been synthesised and their electronic and spectroscopic properties investigated as a function of redox state. Solid state NMR provided insight into the structural features of the POPs, while in situ solid state Vis-NIR and electron paramagnetic resonance spectroelectrochemistry showed that the distinct redox states in POP-S could be reversibly accessed. The development of redox-active porous organic polymers with heterocyclic linkers affords their potential application as stimuli responsive materials in gas storage, catalysis, and as electrochromic materials.

Carbazole- and/or triphenylamine-based D–π–D multiarylamino dyes: synthesis, characterization and photophysical properties

One-photon and two-photon fluorescence quenching by benzoyl peroxide of D–π–D multiarylamino dyes was investigated.

Turn-on fluorescent sensor for the detection of cyanide based on a novel dicyanovinyl phenylacetylene

A novel phenylacetylene derivative (3) was successfully synthesized via Sonogashira coupling and a Knoevenagel reaction for cyanide ion detection.

Proton triggered emission and selective sensing of picric acid by the fluorescent aggregates of 6,7-dimethyl-2,3-bis-(2-pyridyl)-quinoxaline

A heteroatom containing organic fluorophore 6,7-dimethyl-2,3-bis-(2-pyridyl)-quinoxaline (BPQ) is weakly emissive in solution but its emission properties are highly enhanced in the aggregated state due to the restriction of intramolecular rotation (RIR) and large amplitude vibrational modes, demonstrating the phenomenon, aggregation induced emission enhancement (AIEE). It has strong proton capture capability, allowing reversible fluorescence switching in basic and acidic medium and the emission color changes from blue to green in the aggregated state through protonation. It has been explained as a competition between intramolecular charge transfers (ICTs) and the AIEE phenomena at a lower pH range (pH ∼1-4). Such behavior enables it as a fluorescent pH sensor for detection in acidic and basic medium. Morphologies of the particles are characterized using optical and field emission scanning electron microscopic (FESEM) studies. The turn off fluorescence properties of aggregated BPQ have been utilized for the selective detection of picric acid and the fluorescence quenching is explained due to ground state complexation with a strong quenching constant, 7.81 × 10(4) M(-1).

Highly Fluorescent Pyrene-Functional Polystyrene Copolymer Nanofibers for Enhanced Sensing Performance of TNT

A pyrene-functional polystyrene copolymer was prepared via 1,3-dipolar cycloaddition reaction (Sharpless-type click recation) between azide-functional styrene copolymer and 1-ethynylpyrene. Subsequently, nanofibers of pyrene-functional polystyrene copolymer were obtained by using electrospinning technique. The nanofibers thus obtained, found to preserve their parent fluorescence nature, confirmed the avoidance of aggregation during fiber formation. The trace detection of trinitrotoluene (TNT) in water with a detection limit of 5 nM was demonstrated, which is much lower than the maximum allowable limit set by the U.S. Environmental Protection Agency. Interestingly, the sensing performance was found to be selective toward TNT in water, even in the presence of higher concentrations of toxic metal pollutants such as Cd(2+), Co(2+), Cu(2+), and Hg(2+). The enhanced sensing performance was found to be due to the enlarged contact area and intrinsic nanoporous fiber morphology. Effortlessly, the visual colorimetric sensing performance can be seen by naked eye with a color change in a response time of few seconds. Furthermore, vapor-phase detection of TNT was studied, and the results are discussed herein. In terms of practical application, electrospun nanofibrous web of pyrene-functional polystyrene copolymer has various salient features including flexibility, reproducibility, and ease of use, and visual outputs increase their value and add to their advantage.

Fluorescence based explosive detection: from mechanisms to sensory materials

The detection of explosives is one of the current pressing concerns in global security. In the past few decades, a large number of emissive sensing materials have been developed for the detection of explosives in vapor, solution, and solid states through fluorescence methods. In recent years, great efforts have been devoted to develop new fluorescent materials with various sensing mechanisms for detecting explosives in order to achieve super-sensitivity, ultra-selectivity, as well as fast response time. This review article starts with a brief introduction on various sensing mechanisms for fluorescence based explosive detection, and then summarizes in an exhaustive and systematic way the state-of-the-art of fluorescent materials for explosive detection with a focus on the research in the recent 5 years. A wide range of fluorescent materials, such as conjugated polymers, small fluorophores, supramolecular systems, bio-inspired materials and aggregation induced emission-active materials, and their sensing performance and sensing mechanism are the centerpiece of this review. Finally, conclusions and future outlook are presented and discussed.

MEISENHEIMER COMPLEX BETWEEN 2,4,6-TRINITROTOLUENE AND 3-AMINOPROPYLTRIETHOXYSILANE AND ITS USE FOR A PAPER-BASED SENSOR

2,4,6-Trinitrotoluene (TNT) forms a red-colored Meisenheimer complex with 3-aminopropyltrenthoxysilane (APTES) both in solution and on solid phase. The TNT-APTES complex is unique since it forms yellow-colored complexes with 2,4,6-trinitrophenol and 4-nitrophenol, and no complex with 2,4-dinitrotoluene. The absorption spectrum of TNT-APTES has two absorption bands at 530 and 650 nm, while APTES complexes with 2,4,6-trinitrophenol and 4-nitrophenol have absorption maxima at around 420 nm, and no absorption change for 2,4-dinitrotoluene. The TNT-APTES complex facilitates the exchange of the TNT-CH3 proton/deuteron with solvent molecules. The red color of TNT-APTES is immediately visible at 1 µM of TNT.

Self-assembled discrete molecules for sensing nitroaromatics

Efficient sensing of trace amount nitroaromatic (NAC) explosives has become a major research focus in recent time due to concerns over national security as well as their role as environment pollutants. NO2 -containing electron-deficient aromatic compounds, such as picric acid (PA), trinitrotoluene (TNT), and dinitrotoluene (DNT), are the common constituents of many commercially available chemical explosives. In this article, we have summarized our recent developments on the rational design of electron-rich self-assembled discrete molecular sensors and their efficacy in sensing nitroaromatics both in solution as well as in vapor phase. Several π-electron-rich fluorescent metallacycles (squares, rectangles, and tweezers/pincers) and metallacages (trigonal and tetragonal prisms) have been synthesized by means of metal-ligand coordination-bonding interactions, with enough internal space to accommodate electron-deficient nitroaromatics at the molecular level by multiple supramolecular interactions. Such interactions subsequently result in the detectable fluorescence quenching of sensors even in the presence of trace quantities of nitroaromatics. The fascinating sensing characteristics of molecular architectures discussed in this article may enable future development of improved sensors for nitroaromatic explosives.

The electronic, optical and magnetic consequences of delocalization in multifunctional donor–acceptor organic polymers

Redox reactions on electroactive donor–acceptor polymers can be used to tune their response to external magnetic and electrical stimuli.

A pyrene based Schiff base probe for selective fluorescence turn-on detection of Hg2+ ions with live cell application

A novel pyrene based free thiol containing a Schiff base derivative PT1 was synthesized and reported as a fluorescence turn-on sensor for Hg²⁺ ions, via CHEF and excimer (PT1-PT1*) formation with live cell imaging.

Putting corannulene in its place. Reactivity studies comparing corannulene with other aromatic hydrocarbons

Reactivity studies have been used to order a series of polycyclic aromatic hydrocarbons, demonstrating that the curved species corannulene has comparable reactivity to triphenylene.

The mechanism of 2,4,6-trinitrotoluene detection with amino acid-capped quantum dots: a density functional theory study

Both a Meisenheimer complex and deprotonated TNT are formed when TNT meets amino acid-capped quantum dots.

Highly sensitive detection of 2,4,6-trinitrophenol (TNP) based on lysozyme capped CdS quantum dots

This work presents a novel method for nitroaromatic compound detection using lysozyme-capped CdS quantum dots (Lys-CdS QDs).

Fluorescent phenylethynylene calix[4]arenes for sensing TNT in aqueous media and vapor phase

The upper-rim of calix[4]arene is modified with phenylacetylene derivatives via Sonogashira coupling reaction to produce a wider cavity for entrapping TNT.

Ultrafast on-site selective visual detection of TNT at sub-ppt level using fluorescent gold cluster incorporated single nanofiber

Single nanofiber embedded fluorescent gold cluster based sensor for selective detection of TNT at sub-ppt level.

Charge transfer aided selective sensing and capture of picric acid by triphenylbenzenes

A new triaminophenylbenzene based fluorescent chemo-sensor has been synthesized and successfully employed for the selective fluorescence detection of picric acid.

π-Electron rich small molecule sensors for the recognition of nitroaromatics

In this review article we provide an overview of the recent developments made in small molecule-based turn-off fluorescent sensors for nitroaromatic explosives with special focus on organic and H-bonded supramolecular sensors.

Chromogenic ‘naked eye’ and fluorogenic ‘turn on’ sensor for mercury metal ion using thiophene-based Schiff base

2-((3-Methylthiophen-2-yl)methyleneamino)benzenethiol (Probe 1) is selective for Hg²⁺. The binding affinity of Hg²⁺ with Probe 1 was confirmed by DFT and electrochemical behaviour. The limit of detection was 20 μM with 2 : 1 stoichiometry of 1 + Hg²⁺ complex.