Advances in Molecular Design and Photophysical Engineering of Perylene Bisimide-Containing Polyads and Multichromophores for Film-Based Fluorescent Sensors

Recent advances in active chromophores for detecting gamma-hydroxybutyric acid (GHB)-related illicit drugs

Gamma-hydroxybutyric acid (GHB) and its related illicit drugs are of particular forensic interest owing to their abuse as recreational drugs and implications in drug-facilitated sexual assault. The rapid and complete metabolism of GHB in the body results in a short evidence collection window for forensic experts, and challenges exist in simultaneously differentiating between exogenous addition in spiked drinking and low endogenous levels of GHB. Consequently, the development of real-time and on-site detection strategies for GHB plays vital roles in tackling drug-facilitated crimes. Recently, fluorescent and colorimetric strategies have emerged as promising approaches in this field, offering multiple merits of high sensitivity and specificity, ease of handling, and cumulative signaling effects. This minireview outlines the endogenous levels of GHB in the body and possible metabolism pathways, summarizes the recent advances in active chromophores, elucidates the corresponding sensing characteristics, and then exemplifies the developed sensing strips and detection kits based on the optimized chromophores mostly in the past five years. Additionally, the perspectives of the relevant studies are discussed in detail.

Fluorescent Non-conventional D-π-A Organogel for Aniline Sensing

A non-conventional organogelator with rigid chemical structure was designed based on 2,6-distyryl-4H-pyran skeleton in this work. Aided by balanced intermolecular π-π interactions, the gelator was capable of gelate pure chloroform and mixed solutions containing chloroform. Interestingly, introducing long hexyl chains in the gelator's structure makes it lose the gelation ability, indicating that alkyl chain is not always favorable auxiliary group for gelation. The gel network was selectively responsive to aniline, which was manifested by aniline-triggered gel collapse. Notably, the gel exhibited remarkable fluorescence blue-shift upon exposure to aniline, rather than quenching, exhibiting ratiometric fluorescence response. The selective response to aniline was due to that aniline could break the original intermolecular π-π interactions in the gel state, providing a unique example of ratiometric gel sensor for aniline.

Recent Advances in Tetra-Coordinate Boron-Based Photoactive Molecules for Luminescent Sensing, Imaging, and Anticounterfeiting

Tetra-coordinate boron-based fluorescent materials hold considerable promise across chemistry, biology and materials science due to their unique and precisely tunable optoelectronic properties. The incorporation of the heteroatom boron (B) enables these materials to exhibit high luminescence quantum yields, adjustable absorption and emission wavelengths, and exceptional photostability. This review examines the molecular design and applications of tetra-coordinate boron-based photoactive molecules, highlighting their roles in fluorescence sensing, anticounterfeiting, and imaging. We outline how structural features impact their properties and discuss strategies for enhancing their performance, including ligand modification and the extension of conjugation length, among others. Additionally, future research focus in this field is also addressed including strategies for diversifying molecular structures and enhancing molecular stability, which is believed to pave the way for innovative solutions to the challenges in areas such as sensing, imaging and information security.

Dynamic response and discrimination of gaseous sarin using a boron‐difluoride complex film‐based fluorescence sensor

This study presents a novel boron‐difluoride complex‐based fluorescent nanofilm sensor capable of detecting sarin vapors in the environment by reporting an output fluorescence signal. The sensor's evaluation demonstrated an exceptionally low detection limit for sarin vapor, even in the presence of various interfering gases, with theoretical and practical limits of detection of 0.7 and 1 ppb, respectively. The sensor featured a rapid response time (less than 2 s), a broad linear detection range (1 ppb–1000 ppm), and superior selectivity for sarin vapor over a group of interfering analytes, outperforming existing sarin sensors. Mechanistic study indicates that the sensor's heightened sensitivity to sarin vapor is due to the robust affinity of nitrogen atoms within the core BODIQ unit for sarin. Additionally, the tetraphenylethylene structure with steric hindrance effectively inhibits the tight packing of BODIQ derivatives, and forms numerous microporous structures in the self‐assembled nanofilm, which are beneficial for the mass transfer, enhancing the sensor efficiency in detecting vapors. Furthermore, we have achieved the differentiation of sarin, diethyl chlorophosphate, and HCl vapor through the analysis of sensing kinetic. This fluorescent sensor opens new avenues for sustainable, low‐cost, and environment‐friendly portable devices, as well as for environmental monitoring and tracking applications.

Integrated Sensing Platform Validated for the Efficient and On-Site Screening of Amine-Containing Illicit Drugs

Efficient and reliable technologies for the on-site detection of illicit drugs are important in drug-facilitated crime investigations. However, the development of such technologies is challenging. Based on the synthetic optimization, introducing a boron ester functional group to the two furanic indicators endows the stimulus-responsive properties synergistically. The ring-opening reaction of the indicators in the presence of amine-containing illicit drugs generated well-known donor-acceptor Stenhouse adducts, accompanied by strong color changes. A small-size and lightweight laminated sensor was integrated based on the outstanding ratiometric variations of the two active furanic indicators. A prototype platform was fabricated equipped with a circuit control, a mini pump, and a signal processing system. A user-friendly detection and efficient screening of amine-containing illicit drugs, including phenethylamines, amphetamines, cathinones, and tryptamines in the liquid states were conducted. The ratiometric response of the sensor was linear in the concentration range of 2.1-10.6 μg·mL-1 for methamphetamine·HCl and methcathinone ·HCl. The detection limits for the two illicit drugs at the sublevel (ng·mL-1) were found to be 8.4 and 9.0 ng·mL-1, respectively. Double-blind field tests and different illicit drugs were evaluated with good screening capability. Successful trials showed the potential applications of the developed prototype platform for efficient and on-site analytical determination.

Multicolor Tuning of Perylene Diimides Dyes for Targeted Organelle Imaging In Vivo

The adjustment of the emission wavelengths and cell permeability of the perylene diimides (PDI) for multicolor cell imaging is a great challenge. Herein, based on a bay-region substituent engineering strategy, multicolor perylene diimides (MCPDI) were rationally designed and synthesized by introducing azetidine substituents on the bay region of PDIs. With the fine-tuned electron-donating ability of the azetidine substituents, these MCPDI showed high brightness, orange, red, and near infrared (NIR) fluorescence along with Stokes shifts increasing from 35 to 110 nm. Interestingly, azetidine substituents distorted to the plane of the MCPDI dyes, and the twist angle of monosubstituted MCPDI was larger than that of disubstituted MCPDI, which might efficiently decrease their π-π stacking. Moreover, all of these MCPDI dyes were cell-permeable and selectively stained various organelles for multicolor imaging of multiple organelles in living cells. Two-color imaging of lipid droplets (LDs) and other organelles stained with MCPDI dyes was performed to reveal the interaction between the LDs and other organelles in living cells. Furthermore, a NIR-emitting MCPDI dye with a mitochondria-targeted characteristic was successfully applied for tumor-specific imaging. The facile synthesis, excellent stability, high brightness, tunable fluorescence emission, and Stokes shifts make these MCPDI promising fluorescent probes for biological applications.

Molecular design and architectonics towards film-based fluorescent sensing

The past few decades have witnessed encouraging progress in the development of high-performance film-based fluorescent sensors (FFSs) for detecting explosives, illicit drugs, chemical warfare agents (CWAs), and hazardous volatile organic chemicals (VOCs), among others. Several FFSs have transitioned from laboratory research to real-world applications, demonstrating their practical relevance. At the heart of FFS technology lies the sensing films, which play a crucial role in determining the analytes and the resulting signals. The selection of sensing fluorophores and the fabrication strategies employed in film construction are key factors that influence the fluorescence properties, active-layer structures, and overall sensing behaviors of these films. This review examines the progress and innovations in the research field of FFSs over the past two decades, focusing on advancements in fluorophore design and active-layer structural engineering. It underscores popular sensing fluorophore scaffolds and the dynamics of excited state processes. Additionally, it delves into six distinct categories of film fabrication technologies and strategies, providing insights into their advantages and limitations. This review further addresses important considerations such as photostability and substrate effects. Concluding with an overview of the field's challenges and prospects, it sheds light on the potential for further development in this burgeoning area.

Precise synthesis of BN embedded perylene diimide oligomers for fast-charging and long-life potassium-organic batteries

Replacing the C[double bond, length as m-dash]C bond with an isoelectronic BN unit is an effective strategy to tune the optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, precise control of the BN orientations in large PAH systems is still a synthetic challenge. Herein, we demonstrate a facile approach for the synthesis of BN embedded perylene diimide (PDI) nanoribbons, and the polarization orientations of the BN unit were precisely regulated in the two PDI trimers. These BN doped PDI oligomers show great potential as organic cathodes for potassium-ion batteries (PIBs). In particular, trans-PTCDI3BN exhibits great improvement in voltage potential, reversible capacities (ca. 130 mA h g-1), superior rate performance (19 s to 69% of the maximum capacity) and ultralong cyclic stability (nearly no capacity decay over 30 000 cycles), which are among those of state-of-the-art organic-based cathodes. Our synthetic approach stands as an effective way to access large PAHs with precisely controlled BN orientations, and the BN doping strategy provides useful insight into the development of organic electrode materials for secondary batteries.

Bay-Substitution of Perylene Bisimides with Bidentate Nucleophiles: The Case of Aryloxide Anions

In this study, we delve into the regioselectivity of nucleophilic reactions involving brominated perylene bisimides (PBIs) and various bidentate aryloxide anions, previously associated with an SRN1 mechanism. We present herein a new perspective, suggesting that a single-electron-transfer aromatic nucleophilic substitution (SeT-SNAr) mechanism is a more plausible scenario. Our study reveals the favorable impact of photostimulation on reaction yields, making our method a convenient approach for accessing O-arylated PBIs.

Fast and Selective Luminescent Sensing by Langmuir-Schaeffer Films Based on Controlled Assembly of Perylene Bisimide Modified with A Cyclometalated AuIII Complex

Condensed films of functional luminophores dominated by the magnitude and dimensionality of the intermolecular interactions play important roles in sensing performance. However, controlling the molecular assembly and regulating photophysical properties remain challenging. In this study, a new luminophore, ortho-PBI-Au, was synthesized by anchoring a cyclometalated alkynyl-gold(III) unit at the ortho-position of perylene bisimide. An unprecedented T-type packing model driven by weak Au-π interaction and Au-H bonds was observed, laying foundation for striking properties of the luminophore. Controlled assembly of ortho-PBI-Au at the air-water interface, realized using the classical Langmuir-Schaeffer technique, afforded the obtained luminescent films with different packing structures. With an optimized film, sensitive, selective, and rapid detection of a hazardous new psychoactive substance, phenylethylamine (PEA), was achieved. The detection limit, response time, and recovery time were <4 ppb, <1 s, and <5 s, respectively, surpassing the performance of the PEA sensors known thus far. The relationship between the characters of films and the sensing performance was systematically examined by grey relational analysis (GRA). The present study suggests that designing novel molecular aggregation with definite adlayer structure is a crucial strategy to enhance the sensing performance, which could be favorable for the film-based fluorescent sensors.

Structure and Photonic Properties of a Perylenediimide Monolayer Assembled by the Langmuir-Blodgett Technique

The photonic responses of densely packed dye molecule assemblies are strongly dependent on their organization and environment. The precise control of molecular orientations and distances relative to the substrate and to each other is thus a key point in the design of photonic molecular materials. Herein, we report the preparation of a homogeneous and well-organized single monolayer of the perylenediimide (PDI) derivative by means of the Langmuir-Blodgett technique. Its optical properties disclose an intense charge-transfer excitonic absorption band related to important intermolecular coupling. Furthermore, an important immunity to photobleaching is observed for such a molecular assembly. The dipolar orientations of the molecules along the substrate have been unambiguously determined by angle-of-incidence-resolved polarized absorption and back-focal-plane fluorescence mapping. In addition, time-resolved spectroscopy reveals a fast two-dimensional diffusion of excitons consistent with strong π-stacking of adjacent PDI molecules.

Comparative Observation of Distinct Dynamic Stokes Shifts in Diaryl BODIPY Triads with Broadband Two-Photon Absorption

Time-resolved evolution of excited states in the twist-conjugated chromophores is of great fundamental interest for photoluminescent applications. The four diaryl BODIPY triads modified with diverse end-cappers at 2,6-positions were investigated properly, and considerable two-photon absorption capabilities in the first biological spectral window were obtained. Fast relaxations from the initially twisted conformation to the planarized conformation in the excited state were resolved spectrally and kinetically, accompanied by the discernible phenomenon of the fluorescence dynamic Stokes shift (DSS). Along with increasing electron donating capabilities and solvent polarities, the characteristics of structural rearrangement and intramolecular charge transfer have been estimated by enhanced DSS behaviors. Especially, the blue-shifted DSS was rationalized as the sequence conversion between the planarized state and the twisted charge transfer state. A molecular-level picture for relaxation pathways in different polarities was depicted and supported by the theoretical simulations. Significant and fast structural motions in this work contribute to the excited-state dynamics and rational development of versatile BODIPY chromophores.

Tunable Non-Kasha Behaviors and Excited-State Dynamics of Quadrupolar Squaraine Aggregates

Versatile coupling theories have been developed for rationalizing unusual aggregation phenomena of multipolar chromophores. Here, diverse excitonic couplings of a quadrupolar squaraine dye protonated by trifluoroacetic acid could be achieved and tuned unprecedentedly in different solvation media. Subtle changes of the solvent and ion pair influenced the aggregation of the donor-acceptor-donor (D-A-D)-type SQC6 and led to significant variations in optical properties. In contrast to conventional H/J aggregates, strong spectroscopic evidence of nonfluorescent and red-shifted hJ aggregation was obtained. Assumptions of the excitonic interplay with variable strength stabilized by the synergic contributions of π-π stacking and electronic interaction were addressed. Comparative excited-state dynamics in the aggregates clarified the distinctive excitonic coupling of adjacent quadrupolar molecules and the nature of the excited state beyond the dimers. Meanwhile, dominant two-photon absorption transitions could be elucidated by a resonance-enhanced mechanism. The present unusual molecular interplay provides a strategy to fine tune the optical properties of multipolar aggregates.