Bithiophene-Based Donor-π-Acceptor Compounds Exhibiting Aggregation-Induced Emission as Agents to Detect Hidden Fingerprints and Electrochromic Materials

A group of bithiophenyl compounds comprising the cyanoacrylate moiety were designed and successfully synthesized. The optical, (spectro)electrochemical, and aggregation-induced emission properties were studied. DFT calculations were used to explain the reaction's regioselectivity and to determine the molecules' energy parameters (i.e., band gaps, HOMO levels, and LUMO levels). The aggregation-induced emission of compounds has been studied in the mixture of DMF (as a good solvent) and water (as a poor solvent), with different water fractions ranging from 0% to 99%. It has been shown that there are differences in the physicochemical properties of the obtained compounds due to the length of the alkyl chain in the ester group. Investigated derivatives were tested for their potential use in visualizing latent fingerprints and electrochromic materials.

Aggregation-induced emissive nanoarchitectures for luminescent solar concentrators

Aggregation-induced emission (AIE), the phenomenon by which selected luminophores undergo the enhancement of emission intensity upon aggregation, has demonstrated potential in materials and biomaterials science, and in particular in those branches for which spectral management in the solid state is of fundamental importance. Its development in the area of luminescent spectral conversion devices like luminescent solar concentrators (LSCs) is instead still in its infancy. This account aims at summarizing relevant contributions made in this field so far, with a special emphasis on the design of molecular and macromolecular architectures capable of extending their spectral breadth to the deep-red (DR) and the near-infrared (NIR) wavelengths. Because of the many prospective advantages characterizing these spectral regions in terms of photon flux density and human-eye perception, it is anticipated that further development in the design, synthesis and engineering of advanced molecular and macromolecular DR/NIR-active AIE luminophores will enable faster and easier integration of LSCs into the built environment as highly transparent, active elements for unobtrusive light-to-electricity conversion.

Aggregation-induced emission luminogens for latent fingerprint detection

For over a century, fingerprints have served as a pivotal tool for identification of individuals owing to their enduring characteristics and easily apparent features, particularly in the realm of criminal investigations. Latent fingerprints (LFPs) are "invisible fingerprints" that are most commonly available at crime scenes and require a rapid, selective, sensitive, and convenient method for detection. However, existing fingerprint development techniques harbour limitations, prompting the exploration of novel approaches that prioritize investigator safety and environmental sustainability. Leveraging the unique photophysical properties of aggregation-induced emission luminogens (AIEgens) has emerged as a promising strategy for on-site analysis of LFP visualization. In this highlight, we have presented a comparative analysis of various AIEgens (organic compounds, metal complexes, nanoparticles, and polymers) for the development and detection of LFPs. Through this examination, insights into the efficiency and potential applications of AIE-based fingerprint development techniques are provided. In addition, several strategies have been proposed for circumventing the limitations of existing AIEgens. We hope that this highlight article will encourage more researchers to investigate AIEgens in LFP detection, contributing to forensic science.

Development research of latent fingermarks based on aggregation-induced emission technique

Fingerprints hold evidential value for individual identification; a sensitive, efficient, and convenient method for visualizing latent fingermarks (LFMs) is of great importance in the field of crime scene investigation. In this study, we proposed an aggregation-induced emission atomization technique (AIE-AT) to obtain high-quality fingermark images. Six volunteers made over 1566 fingerprint samples on 17 different objects. The quality of fingermark development was evaluated using grayscale analysis for quantitative assessment, combining the fluency of fingermark ridges and the degree of level 2 and level 3 features. Both qualitative and quantitative methods were employed to explore the effectiveness of AIE molecule C27H19N3SO in developing fingermarks, its applicability to objects, and its individual selectivity. Additionally, the stability of the AIE molecule was examined. Comparative experimental results demonstrated the high stability of the AIE molecule, making it suitable for long-term preservation. The grayscale ratio of the ridges and furrows was at least 2, with high brightness contrast, the level 2 and level 3 features were clearly observable. The AIE-AT proved to be effective for developing fingermarks on nonporous, porous, and semiporous objects. It exhibited low selectivity on suspects who leave fingermarks and showed better development effects on challenging objects, as well as efficient extraction capability for in situ fingermarks. In summary, AIE-AT can efficiently develop latent fingermarks on common objects and even challenging ones. It locates the latent fingermarks for further accurate extraction of touch exfoliated cells in situ, providing technical support for the visualization of fingermarks and the localization for extraction of touch DNA.

Enhanced intramolecular charge transfer and near-infrared fluorescence in 4-dimethylamino-chalcone analogues through extended conjugation: synthesis, photophysical properties, and theoretical modelling

The distinctive characteristics of near-infrared fluorescent organic molecules render them indispensable across diverse applications, from energy harvesting to bioimaging and sensing technologies. In this work, we continue our investigation on the chalcone derivative, 4-dimethylamino-2'-hydroxychalcone (nDHC, n = 1; where n is the number of olefinic bonds), by expanding the number of central double bonds (n = 2 (2DHC) and n = 3 (3DHC)). Additionally, we also synthesized the structurally related chalcones lacking the OH group (DC, 2DC, 3DC) in order to obtain a comprehensive understanding of their effects on the intramolecular charge transfer (ICT). The results show remarkable bathochromic shifts in absorption and fluorescence peaks in solution as n increases. These shifts, 20 nm and 35 nm for absorption and 100 nm and 200 nm for fluorescence in 2DHC and 3DHC, respectively, signify enhanced ICT and a significant increase in the excited state's dipole moment. The presence of OH groups notably amplifies these shifts due to additional electron donation, influencing solute-solvent interactions in solution. Femtosecond fluorescence upconversion and transient absoprtion techniques unraveled distinct dynamics in these derivatives, exhibiting the dominance of vibrational cooling, solvation, and intramolecular motions, particularly in the larger conjugated systems 3DHC and 3DC. The observed changes in the femtosecond transinet absorption spectra suggest the existence of new active states in extended conjugation systems, indicating diverse intramolecular conformational states contributing to their relaxation dynamics. The results of this study provide invaluable insights into excited-state spectroscopy, offering a roadmap for tailoring chalcone derivatives for specific applications.

A near-infrared AIE fluorescent probe for accurate detection of sulfur dioxide derivatives and visualization of fingerprints

In most biophysiological processes, sulfur dioxide (SO2) is an important intracellular signaling molecule that plays an important role. The change of SO2 in cells are closely related to various diseases such as neurological disorders and lung cancer, so it is necessary to develop fluorescent probes with the ability to accurately detect SO2 during physiological processes. In this work, we designed and synthesized a multifunctional fluorescent probe TIS. TIS has excellent properties such as near-infrared emission, large stokes shift, excellent SO2 detection capabilities, low detection limit, high specificity and visualization of color change before and after reaction. Simultaneously, TIS has low cytotoxicity, good biocompatibility, clear cell imaging capability and mitochondrial targeting ability. In addition, the ability of TIS to be applied to different material surfaces for latent fingerprint fluorescence imaging was also explored. TIS provides an excellent method for the accurate detection of SO2 derivatives and shows great potential applications in near-infrared cellular imaging and latent fingerprint fluorescence imaging.

An ESIPT-Dependent AIE Fluorophore Based on HBT Derivative: Substituent Positional Impact on Aggregated Luminescence and its Application for Hydrogen Peroxide Detection

Aiming to develop the facile organic fluorophore possessing excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE), we designed and synthesized two isomers with different linkage site between hydroxyl of 2-(2-hydroxyphenyl) benzothiazole (HBT) and a benzothiazole substituent (para position refers to p-BHBT and ortho position refers to o-BHBT). Fluorescence emission properties of p-BHBT and o-BHBT in THF/water mixtures with different water volume fractions indicated an opposite luminescence in aggregates, in which p-BHBT showed an ESIPT-dependent AIE properties while o-BHBT displayed ESIPT effect and aggregation-caused quenching (ACQ) qualities. A possible mechanism for molecular actions to illustrate the aggregating luminescence alteration of these two isomers had been proposed and verified by theoretical and experimental studies. More importantly, Probe-1, generated from dual ESIPT-AIE fluorophore p-BHBT, was successfully used as a ratiometric fluorescent chemosensor for highly selective (above 15-fold over other ROS) and sensitive (69-fold fluorescence enhancement with 0.22 μM of detection limit) detection of hydrogen peroxide in aqueous solution and living cells, respectively.

Fluorescent Cationic Conjugated Polymer-Based Adaptive Developing Strategy for Both Sebaceous and Blood Fingerprints

Both latent sebaceous and blood fingerprints may provide valuable information for forensic investigation. To detect both types of fingerprints with no need to predistinguish them, a new adaptive developing strategy was proposed. A cationic conjugated polymer with poly[p-(phenylene ethylene)-alt-(thienylene ethynylene)] backbone (PPETE-NMe₃⁺) was synthesized, which was dissolved in N,N-dimethylformamide (DMF) to form the developing solution. Fingerprints were developed by a simple dropping and incubating process without any pre-/post-treatments. Fluorescent photographs of the developed fingerprints on various substrates demonstrated that this developing strategy was effective for both types of fingerprints on nonporous substrates. Gray value analysis further confirmed the enhancement of the legibility of the fingerprint images. The preliminary mechanism exploration suggested that certain weak interactions, such as hydrophobic interaction and electrostatic interaction, may synergistically contribute to the interaction between the polymer and fingerprint components. The molecular design of the polymer combined with an appropriate solvent endowed the developing system the adaptiveness toward different types of fingerprints. This adaptive developing strategy made the fingerprint-developing process more efficient and may be further extended to more practical application scenes.

A fluorescence turn-on probe for hydrogen sulfide and biothiols based on PET & TICT and its imaging in HeLa cells

In this paper, a photoinduced electron transfer (PET)& twisted intramolecular charge transfer (TICT)-based fluorescent probe (1) for detecting biothiols (GSH/Cys/Hcy) and hydrogen sulfide with fluorescence turn on was developed. The probe could recognize hydrogen sulfide over primary ions and selectively detect GSH/Cys/Hcy over other amino acids with fluorescence turn-on (an ESIPT process). H₂S can be distinguished from GSH/Cys/Hcy with wavelength shift by UV-Vis spectra. In addition, detection limits for H₂S/GSH/Cys/Hcy of probe 1 were 1.42 μM (0-100 μM), 0.13 μM (0-40 μM), 0.27 (0-30 μM), 0.22 μM (0-40 μM), respectively. The proposed thiolysis of the 2,4-dinitrochlorophenyl ether reaction in identification process was verified by the characteristic peak in ¹H NMR and HRMS spectra. Finally, the biological imaging experiments and low cytotoxicity investigations in HeLa cells demonstrated that probe 1 could provide a promising method for the determination of H₂S and biothiols in aqueous solution and living cells.

Molecular design of amino-type hydrogen-bonding molecules for excited-state intramolecular proton transfer (ESIPT)-based fluorescent probe using the TD-DFT approach

A molecular screening of a new series of NH-type molecules for ESIPT-based fluorescent probes has been carried out using time-dependent density. functional theory.

Lighting up forensic science by aggregation-induced emission: A review

Forensic science requires a fast, sensitive, and anti-interfering imaging tool for on-site investigation and bio-analysis. The aggregation-induced emission (AIE) phenomenon exhibits remarkable luminescence properties (large Stokes shift, diverse molecular structures, and high photo-stability), which can provide a viable solution for on-site analysis, while at the same time overcoming the problem of aggregation-caused quenching (ACQ). Based on the outstanding performance in chemical analysis and bio-sensing, AIE materials have great prospects in the field of forensic science. Therefore, the application of AIE in forensic science has been summarized for the first time in this article. After a brief introduction to the concept and development of AIE, its applications in the determination of toxic or hazardous substances, based on data on poisoning deaths, has been summarized. Subsequently, besides the bio-imaging function, other applications of AIE in analyzing markers related to forensic genetics, forensic pathology, (focusing on the corpse) and clinical forensics (focusing on the living) have been discussed. In addition, applications of AIE molecules in criminal investigations, including recognition of fingerprints and blood stains, detection of explosives and chemical warfare agents, and anti-counterfeiting have also been presented. It is hoped that this review will light up the future of forensic science by stimulating more research work on the suitability of AIE materials in advancing forensic science.

TDDFT study on the photophysical properties of coumarinyl chalcones and sensing mechanism of a derived fluorescent probe for hydrogen sulfide

Coumarin-chalcone hybrids have attracted much attention in recent years due to their important optical properties. Herein, the photophysical properties of a series of coumarinyl chalcones and the sensing mechanism for H₂S of a related fluorescent probe CC-DNP were investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The predicted spectral properties agree well with the experimental results, which allowed an assignment of the spectra. Our calculations successfully clarified the experimental observed fluorescence "off-on" effect and the fluorescent quenching mechanism of the probe. The results revealed that the first excited state (S₁) of the probe CC-DNP is a dark state with obvious charge transfer from coumarin unit to 2,4-dinitrophenyl (DNP) moiety, which results in the fluorescence quenching via the nonradiative photoinduced electron transfer (PET) process. On the other hand, the excited state S₁ in the thiolysis product CC-OH decayed directly to S₀, and thus the fluorescence is recovered.

An aggregation-induced emission luminogen combined with a cyanoacrylate fuming method for latent fingerprint analysis

An aggregation-induced emission luminogen tetraphenylethene-based dye FLA-2, was synthesized and characterized. Two methods were adopted herein to visualize the latent fingerprints, respectively.

An aggregation-induced emission active vitamin B6 cofactor derivative: application in pH sensing and detection of latent fingerprints

Aggregation-induced emission (AIE) properties of an easy-to-prepare and structurally planar Schiff base derivative of the vitamin B₆ cofactor pyridoxal (L) were investigated in DMSO–H₂O mixed solvents.

Comparative Photophysical Study of Differently Substituted Cinnamaldehyde-Based Chalcones: From Intramolecular Charge Transfer to Fluorogenic Solvent Selectivity

We synthesized three cinnamaldehyde-based chalcone derivatives, (2E,4E)-1-(2-hydroxyphenyl)-5-phenylpenta-2,4-dien-1-one (HPD), (2E,4E)-5-(4-(dimethylamino)phenyl)-1-phenylpenta-2,4-dien-1-one (DPPD), and (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-hydroxyphenyl)penta-2,4-dien-1-one (DPHPD). The molecule HPD was totally nonfluorescent. Exclusion of a phenolic -OH moiety from HPD along with the introduction of a dimethylamino moiety in DPPD resulted in excellent excited-state charge-transfer properties in the solution phase. Interestingly, introduction of phenolic -OH and dimethylamino moieties in DPHPD resulted in solvent selectivity in the excited state. DPHDP behaved as a strong fluorophore only in carbonyl- or thiocarbonyl-containing solvents, such as dimethylsulfoxide (DMSO), dimethylformamide (DMF) and dimethylacetamide (DMAC) and showed a prominent red color under UV light. However, no emission was observed in similar carbonylated solvents, such as acetone or formamide, or in viscous medium, such as glycerol. The difference in solvent response was probed by various spectroscopic techniques and analyzed using the crystal structure of the three chalcones along with theoretical calculations. The practical utility of DPHPD was explored by detecting the percentage of water in DMSO solvent.

Aggregation-Induced Emission for Visualization in Materials Science

Fluorescent imaging techniques have attracted much attention as a powerful tool to realize the visualization of structural and morphological evolution of various materials. However, the traditional fluorescent dyes usually suffered from aggregation-caused quenching, which severely limits the visualization results. In contrast, aggregation-induced emission (AIE) molecules with high quantum yields in the condensed state showed great opportunities for imaging techniques. In this feature article, recent progresses in visualization with AIE molecules are discussed. Assembly processes including crystallization, gelation process, and dissipative assembly have been observed. To better study information obtained regarding the processes, visualization during reactions, phase transitions, and molecular motions are successfully presented. Based on these successes, AIE molecules were further applied for phase recognition, macro-dispersion evaluation, and damage detection. Finally, we also present the outlook and perspectives, in our opinion, for the development of visualization by AIE molecules.

Excited state proton transfer in 2'-hydroxychalcone derivatives

Fluorophores exhibiting excited-state intramolecular proton transfer (ESIPT) are promising candidates for applications ranging from imaging and probing to laser dyes, optoelectronic devices and molecular logic gates. Recently, ESIPT-active solid-state emitters based on 2'-hydroxychalcone have been synthesized. The compounds are almost non-emissive in solution but emit in the deep red/NIR region when crystalline. Herein, we present a comprehensive theoretical investigation of the gas-phase excited state relaxation pathways in five 2'-hydroxychalcone systems, using a combination of static and non-adiabatic simulations. We identify two competing non-radiative relaxation channels, driven by intramolecular rotation in the enol and keto excited states. Both mechanisms are accessible for the five compounds studied and their relative population depends on the nature of the substituent. The addition of electron-donating substituents greatly increases the propensity of the ESIPT pathway versus rotation in the enol state. The identification of the fundamental relaxation mechanisms is the first step towards understanding the aggregated emission phonomena of these compounds.

AIE + ESIPT based red fluorescent aggregates for visualization of latent fingerprints

DPSA shows applications in establishing the individuality of three subjects using the 1st (pattern of arch, loop or whorl) and 2nd (minutiae details of dots, ridge ending, core and delta) level of information.

New Insight into the Origin of the Red/Near-Infrared Intense Fluorescence of a Crystalline 2-Hydroxychalcone Derivative: A Comprehensive Picture from the Excited-State Femtosecond Dynamics

Fluorescence upconversion and transient absorption techniques are used to explain the source of the intense red/near-infrared emission of crystalline 4-dimethylamino-2'-hydroxychalcone. We found that the initially excited enol form undergoes tautomerization in 3 ps to form the keto tautomer. The latter is stable in the ground state as a consequence of J-type aggregation in the crystal packing and is manifested in an absorption peak at 550 nm that spectrally overlaps with the short-lived enol emission, leading to self-reabsorption and adding a factor to the complete depletion of the enol emission. Relaxation of the keto tautomer takes place in the form of intense fluorescence (600-750 nm) with 1.7 ns lifetime. The different spectroscopy in solution is due to vibrational cooling (300 fs), followed by solvation dynamics (5 ps in methanol) and twisting of the hydroxyphenyl ring (16 ps), before relaxation of the enol tautomer in the form of weak green fluorescence with 350 ps lifetime.

A novel fluorophore based on the coupling of AIE and ESIPT mechanisms and its application in biothiol imaging

A novel fluorophore TPE-HBT was designed based on the intersection of tetraphenylethene (TPE) and 2-(2′-hydroxyphenyl)benzothiazole (HBT).