Long-wavelength Excitations Research Articles

Development of a Photoelectrochemical Microelectrode Using an Organic Probe for Monitoring Hydrogen Sulfide in Living Brains.

Hydrogen sulfide (H2S) is an important bioactive molecule that plays a significant role in various functions, particularly in the living brain, where it is closely linked to cognition, memory, and several neurological diseases. Consequently, developing effective detection methods for H2S is essential for studying brain functions and the underlying mechanisms of these diseases. This study aims to construct a novel photoelectrochemical (PEC) microelectrode Ti/TiO2@HSP for the quantitative monitoring of H2S levels in the living brain. The PEC microelectrode Ti/TiO2@HSP is formed by covalently bonding a specifically designed organic PEC probe HSP, which possesses a D-π-A structure, to the surface of TiO2 nanotubes generated via in situ anodic oxidation of titanium wire. The PEC probe HSP can effectively react with H2S and generate significant photocurrent response under long-wavelength excitation light (560 nm), thereby achieving quantitative detection of H2S. The sensor demonstrates high sensitivity and good selectivity. In vivo experiments utilizing the PEC microelectrode Ti/TiO2@HSP enable the monitoring of dynamic changes in H2S levels across various regions of the mouse brain. The findings reveal that in normal mice, the concentration of H2S in the hippocampus is significantly higher than in the striatum and cerebral cortex. Additionally, following propargylglycine drug stimulation, H2S concentrations in different brain regions were observed to decrease, with the most substantial reduction noted in the hippocampus. This suggests that cystathionine γ-lyase (CSE) is the primary enzyme responsible for H2S production in this area, while the striatum exhibits a less pronounced decrease in H2S concentration, indicating a reliance on alternative enzymatic pathways for H2S production. Therefore, this study not only successfully develops a high-performance H2S detection sensor but also provides new experimental tools and theoretical foundations for further exploring the roles of H2S in neurophysiological and pathological processes.

Near-infrared xanthene fluorescence probe for frequency upconversion fluorescence detection of HSO3− in evaluation of drug-induced hepatotoxicity

Bisulfite (HSO3−) plays an important role in life activities. Abnormal content of HSO3− may cause cardiovascular, cancer and other diseases. Frequency upconverted luminescent (FUCL) probes are a class of anti-Stokes luminescent materials with long-wavelength excitation and short-wavelength emission properties, which offer advantages in a range of applications due to their higher sensitivity and photostability. In addition, FUCL imaging has the advantages of high tissue penetration depth and low photo-damage, thus, it is more suitable for fluorescence imaging. In this work, a FUCL probe based on an xanthene fluorophore was designed and synthesised to detect HSO3−. The Probe PT-1 could respond to HSO3− and had high selectivity and sensitivity. It also exhibited a quenched FUCL signal. The detection limit of FUCL concerning HSO3− was 43 nM (λex = 730 nm), which is half the detection limit achieved under traditional excitation (93 nM, λex = 643 nm). Cell fluorescence imaging showed that PT-1 could effectively target mitochondria and monitor endogenous/exogenous HSO3− in living cells. More importantly, PT-1 was successfully used to monitor the level of HSO3− in mice with drug-induced liver injury through FUCL imaging.

Oxygen doping induced intramolecular electron acceptor system in red g-C3N4 nanosheets with remarkably enhanced photocatalytic performance

The enhancement of the photocatalytic activity of graphitic carbon nitride (g-C3N4) depends on the rational design of its visible-light harvesting and charge separation/migration properties. Herein, an oxygen doping-induced intramolecular electron acceptor system enabling n→π* electronic transitions in red g-C3N4 nanosheets (Eg ∼ 1.89 eV) was prepared via copolymerization with nitrilotriacetic acid (NTA) and urea. The n→π* electronic transition can be controllably tuned, thus broadening the absorption spectrum of the system to ∼750 nm. Simultaneously, doping with oxygen which acts as an electron acceptor, accelerates in-plane charge separation and migration. Moreover, this strategy was confirmed experimentally to be scalable for industrial mass production. Experiments and theoretical calculations demonstrated that the oxygen doping could continuously modulate the band gap (from ∼2.65 eV to ∼1.32 eV), resulting in the formation of an intramolecular electron acceptor system which enhances charge separation/migration kinetics. The optimized sample exhibited remarkable photocatalytic H2 and H2O2 production rates of ∼144.8 μmol/h and ∼539.76 μM/h, respectively, which are higher than those for currently available g-C3N4-based photocatalysts. Significantly, the sample exhibited H2 and H2O2 photocatalytic yields ∼37.3 and ∼30.1 times those of pristine g-C3N4 under long-wavelength excitation (λ = 520 nm). This study developed an effective and scalable strategy for the design and synthesis of full-spectrum photocatalysts for a broad range of applications.

Room temperature luminescence of 1,N2-etheno-2-aminopurine in poly (vinyl alcohol) films.

We studied spectral properties of 1,N2-etheno-2-aminopurine after immobilization in poly (vinyl alcohol) films. The absorption spectrum of 1,N2-ε2APu consists of two peaks centered at 300 and 370 nm, and the fluorescence spectrum has maximum at about 460 nm. The fluorescence quantum efficiency is 62%. The fluorescence anisotropy reaches a value of 0.3 at longer wavelengths, while it is low at shorter wavelengths (corresponding to the second single excited state). The 1,N2-ε2APu has a relatively long fluorescence lifetime of about 16 ns and a noticeable room temperature phosphorescence with a lifetime of about 220 ms. A broad phosphorescence emission band (425-675 nm) is centered at about 530 nm and markedly overlaps with fluorescence at shorter wavelengths. Surprisingly, the phosphorescence excitation spectrum of 1,N2-ε2APu-doped poly (vinyl alcohol) film differs from the absorption and fluorescence excitation spectra. The strongest room temperature phosphorescence excitation is about 335 nm. At longer excitation wavelengths, above 450 nm, where fluorescence cannot be excited, a triplet excitation is still possible. The 1,N2-ε2APu phosphorescence anisotropy spectra confirm direct triplet state excitation. The ability to excite molecules at long wavelengths can find applications in the study of biological molecules that are unstable when excited at high energies.

A Nanoencapsulated Ir(III)-Phthalocyanine Conjugate as a Promising Photodynamic Therapy Anticancer Agent.

Despite the potential of photodynamic therapy (PDT) in cancer treatment, the development of efficient and photostable photosensitizing molecules that operate at long wavelengths of light has become a major hurdle. Here, we report for the first time an Ir(III)-phthalocyanine conjugate (Ir-ZnPc) as a novel photosensitizer for high-efficiency synergistic PDT treatment that takes advantage of the long-wavelength excitation and near infrared (NIR) emission of the phthalocyanine scaffold and the known photostability and high phototoxicity of cyclometalated Ir(III) complexes. In order to increase water solubility and cell membrane permeability, the conjugate and parent zinc phthalocyanine (ZnPc) were encapsulated in amphoteric redox-responsive polyurethane-polyurea hybrid nanocapsules (Ir-ZnPc-NCs and ZnPc-NCs, respectively). Photobiological evaluations revealed that the encapsulated Ir-ZnPc conjugate achieved high photocytotoxicity in both normoxic and hypoxic conditions under 630 nm light irradiation, which can be attributed to dual Type I and Type II reactive oxygen species (ROS) photogeneration. Interestingly, PDT treatments with Ir-ZnPc-NCs and ZnPc-NCs significantly inhibited the growth of three-dimensional (3D) multicellular tumor spheroids. Overall, the nanoencapsulation of Zn phthalocyanines conjugated to cyclometalated Ir(III) complexes provides a new strategy for obtaining photostable and biocompatible red-light-activated nano-PDT agents with efficient performance under challenging hypoxic environments, thus offering new therapeutic opportunities for cancer treatment.

Unravelling structure evolution of dissolved organic matter during oxidation by persulfate: Insights from aromaticity and fluorescence analysis

Persulfate advanced oxidation technology is widely utilized for remediating organic-contaminated groundwater. Post-remediation by persulfate oxidation, the aromaticity of dissolved organic matter (DOM) in groundwater is significantly reduced. Nevertheless, the evolution trends of aromaticity and related structural changes in DOM remained unclear. Here, we selected eight types of DOM to analyze the variation in aromaticity, molecular weight, and fluorescence characteristics during oxidation by persulfate using optical spectroscopy and parallel faction analysis combined with two-dimensional correlation spectroscopy analysis (2D PARAFAC COS). The results showed diverse trends in the changes of aromaticity and maximum fluorescence intensity (Fmax) among different types of DOM as the reaction time increases. Four types of DOM (humic acid 1S104H, fulvic acid, and natural organic matters) exhibited an initially noteworthy increase in aromaticity followed by a decrease, while others demonstrated a continuous decreasing trend (14.3%–69.4%). The overall decreasing magnitude of DOM aromaticity follows the order of natural organic matters ≈ commercial humic acid > fulvic acid > extracted humic acid. The Fmax of humic acid increased, exception of commercial humic acid. The Fmax of fulvic acid initially decreased and then increased, while that of natural organic matters exhibited a decreasing trend (86.4%). The fulvic acid-like substance is the main controlling factor for the aromaticity and molecular weight of DOM during persulfate oxidation process. The oxidation sequence of fluorophores in DOM is as follows: fulvic-like substance, microbial-derived humic-like substance, humic-like substance, and aquatic humic-like substance. The fulvic-like and microbial-derived humic-like substances at longer excitation wavelengths were more sensitive to the response of persulfate oxidation than that of shorter excitation wavelengths. This result reveals the structure evolution of DOM during persulfate oxidation process and provides further support for predicting its environmental behavior.

Development of Two-Photon Super-Resolution Microscopy

Two-photon excitation microscopy enables in vivo deep-tissue imaging within organisms. This technique is based on two-photon excitation, a nonlinear optical process that uses near-infrared light for excitation, resulting in high tissue permeability. Notably, two-photon excitation occurs only near the focal plane; therefore, minimally invasive tomographic images can be obtained. Owing to these features, two-photon excitation microscopy is currently widely used in medical and life-science research, particularly in the domain of neuroscience for in vivo visualization of deep tissues. However, the use of long-wavelength excitation light in two-photon excitation microscopy has resulted in a larger focused spot size and relatively low spatial resolution, which is a limitation of this technique for further applications. Recent studies have described super-resolution microscopy techniques applied to two-photon excitation microscopy in an attempt to observe living organisms "as they are in their natural state" with high spatial resolution. We have also addressed this topic using an optical approach (two-photon stimulated emission depletion microscopy) and an image analysis approach (two-photon super-resolution radial fluctuation). Here, we describe these approaches together with a discussion of our recent accomplishments.

Hyperbolic response and low-frequency ultra-flat plasmons in inhomogeneous charge-distributed transition-metal monohalides.

Plasmon, the collective oscillations of free electron gas in materials, determines the long-wavelength excitation spectrum and optical response, are pivotal in the realm of nanophotonics and optoelectronics. In this study, using the first-principles calculations, we systematically investigated the dielectric response and plasmon properties of bulk transition-metal monohalides MXs (M = Zr, Mo; X = Cl, F). Due to the strong electronic anisotropy, MXs exhibit a broadband type-II hyperbolic response and direction-dependent plasmon modes. Particularly, local field effect (LFE) driven by the charge distribution inhomogeneity, significantly modifies the optical response and excitation spectra in MX along the out-of-plane direction. Taking into account LFE, the energy dissipation along the out-of-plane direction is almost completely suppressed, and an ultra-flat and long-lived plasmon mode with a slow group velocity is introduced. This finding reveals the role of charge density in modifying the optical response and excitation behavior, shedding light on potential applications in plasmonics.

3D printing-based lateral flow visual assay utilizing the dual-excitation property of nitrogen-doped carbon dots for the ratiometric determination and chemometric discrimination of flavonoids.

A ratiometric fluorescence sensor has been established based on dual-excitation carbon dots (D-CDs) for the detection of flavonoids (morin is chosen as the typical detecting model for flavonoids). D-CDs were prepared using microwave radiation with o-phenylenediamine and melamine and exhibit controllable dual-excitation behavior through the regulation of their concentration. Remarkably, the short-wavelength excitation of D-CDs can be quenched by morin owing to the inner filter effect, while the long-wavelength excitation remains insensitive, serving as the reference signal. This contributes to the successful design of an excitation-based ratiometric sensor. Based on the distinct and differentiated variation of excitation intensity, morin can be determined from 0.156 to 110µM with a low detection limit of 0.156µM. In addition, an intelligent and visually lateral flow sensing device is developed for the determination of morin content in real samples with satisfying recoveries, which indicates the potential application for human health monitoring.

Multifunctional agents based on 3-dicycanovinylindan-1-one acceptor: Molecular design and phototheranostic application.

Phototherapy, including photodynamic therapy (PDT) and photothermal therapy (PTT), has garnered considerable attention in recent years, owing to its precise spatiotemporal accuracy with minimal side effects. Recent research reveals that the combination of PDT and PTT exhibits a remarkable anti-tumor efficacy compared to PDT or PTT alone, which has put forward the new requirements of multifunctional phototherapy agents with both high photosensitization and photothermal conversion efficiencies. Among the newly developed multifunctional agents, the ones with one or two 3-dicycanovinylindan-1-one (IC) moieties as the acceptors attract much more attention, due to their long-wavelength excitation and emission, as well as high phototherapy efficacies. Therefore, in this review, the latest advancement of multifunctional agents based on IC acceptor is summarized. Especially, we focus on the structure-property relationships of the agents, as well as their biomedical application in anti-tumor therapy or image-guided therapy. Our perspective on the further future development of this field is also discussed to conclude.

Symmetry-Breaking Triplet Excited State Enhances Red Afterglow Enabling Ubiquitous Afterglow Readout.

Molecular vibrations are often factors that deactivate luminescence. However, if there are molecular motion elements that enhance luminescence, it may be possible to utilize molecular movement as a design guideline to enhance luminescence. Here, the authors report a large contribution of symmetry-breaking molecular motion that enhances red persistent room-temperature phosphorescence (RTP) in donor-π-donor conjugated chromophores. The deuterated form of the donor-π-donor chromophore exhibits efficient red persistent RTP with a yield of 21% and a lifetime of 1.6s. A dynamic calculation of the phosphorescence rate constant (kp) indicates that the symmetry-breaking movement has a crucial role in selectively facilitating kp without increasing nonradiative transition from the lowest triplet excited state. Molecules exhibiting efficient red persistent RTP enable long-wavelength excitation, indicating the suitability of observing afterglow readout in a bright indoor environment with a white-light-emitting diode flashlight, greatly expanding the range of anti-counterfeiting applications that use afterglow.

Recent progress of UCNPs-MoS2 nanocomposites as a platform for biological applications.

Composite materials can take advantages of the functional benefits of multiple pure nanomaterials to a greater degree than single nanomaterials alone. The UCNPs-MoS2 composite is a nano-application platform that combines upconversion luminescence and photothermal properties. Upconversion nanoparticles (UCNPs) are inorganic nanomaterials with long-wavelength excitation and short-wavelength tunable emission capabilities, and are able to effectively convert near-infrared (NIR) light into visible light for increased photostability. However, UCNPs have a low capacity for absorbing visible light, whereas MoS2 shows better absorption in the ultraviolet and visible regions. By integrating the benefits of UCNPs and MoS2, UCNPs-MoS2 nanocomposites can convert NIR light with a higher depth of detection into visible light for application with MoS2 through fluorescence resonance energy transfer (FRET), which compensates for the issues of MoS2's low tissue penetration light-absorbing wavelengths and expands its potential biological applications. Therefore, starting from the construction of UCNPs-MoS2 nanoplatforms, herein, we review the research progress in biological applications, including biosensing, phototherapy, bioimaging, and targeted drug delivery. Additionally, the current challenges and future development trends of UCNPs-MoS2 nanocomposites for biological applications are also discussed.

Lanthanide complexes with an azo-dye chromophore ligand: syntheses, crystal structures, and near-infrared luminescence by long-wavelength excitation.

Near-infrared (NIR) emissive probes are becoming increasingly popular in biological sensing and imaging due to the advantages of non-invasiveness and deep tissue-penetrating ability. Herein, a series of complexes of trivalent lanthanide ions (Ln = Yb, Er, and Gd) with the commercially available azo dye chromophore 2R (Na2H2C2R) as ligand and featuring respectively H2O and dimethylsulfoxide (DMSO) as ancillary ligands have been prepared. Formulated as [Ln2(HC2R)2(H2O)10]·8H2O (1-3, Ln = Yb, Er, Gd) and [Ln2(HC2R)2(DMSO)10]·2DMSO (4-6, Ln = Yb, Er, Gd), their structures have been determined by single-crystal X-ray diffraction studies. Photophysical property studies revealed NIR emissions of the DMSO complexes characteristic of Yb(III) and Er(III), effectively sensitized by the dye ligand arising mainly from the π-π* transition of the chromophore. The long-wavelength excitation of the complexes, covering the whole visible-light range and extending into the NIR region, portends the potential applications of such complexes for flexible bioimaging and sensing.

Lanthanide-doped upconversion nanoparticles as nanoprobes for bioimaging.

Upconversion nanoparticles (UCNPs) are a class of nanomaterials composed of lanthanide ions with great potential for paraclinical applications, especially in laboratory and imaging sciences. UCNPs have tunable optical properties and the ability to convert long-wavelength (low energy) excitation light into short-wavelength (high energy) emission in the ultraviolet (UV)-visible and near-infrared (NIR) spectral regions. The core-shell structure of UCNPs can be customized through chemical synthesis to meet the needs of different applications. The surface of UCNPs can also be tailored by conjugating small molecules and/or targeting ligands to achieve high specificity and selectivity, which are indispensable elements in biomedical applications. Specifically, coatings can enhance the water dispersion, biocompatibility, and efficiency of UCNPs, thereby optimizing their functionality and boosting their performance. In this context, multimodal imaging can provide more accurate in vivo information when combined with nuclear imaging. This article intends to provide a comprehensive review of the core structure, structure optimization, surface modification, and various recent applications of UCNPs in biomolecular detection, cell imaging, tumor diagnosis, and deep tissue imaging. We also present and discuss some of their critical challenges, limitations, and potential future directions.

Supramolecular red-light-photosensitized nitric oxide release with fluorescence self-reporting within biocompatible nanocarriers.

The strict dependence of the biological effects of nitric oxide (NO) on its concentration and generation site requires this inorganic free radical to be delivered with precise spatiotemporal control. Light-activation by suitable NO photoprecursors represents an ideal approach. Developing strategies to activate NO release using long-wavelength excitation light in the therapeutic window (650-1300 nm) is challenging. In this contribution, we demonstrate that NO release by a blue-light activatable NO photodonor (NOPD) with self-fluorescence reporting can be triggered catalytically by the much more biocompatible red light exploiting a supramolecular photosensitization process. Different red-light absorbing photosensitizers (PSs) are co-entrapped with the NOPD within different biocompatible nanocarriers such as Pluronic® micelles, microemulsions and branched cyclodextrin polymers. The intra-carrier photosensitized NO release, involving the lowest, long-lived triplet state of the PS as the key intermediate and its quenching by the NOPD, is competitive with that by molecular oxygen. This allows NO to be released with good efficacy, even under aerobic conditions. Therefore, the adopted general strategy provides a valuable tool for generating NO from an already available NOPD, otherwise activatable with the poorly biocompatible blue light, without requiring any chemical modification and using sophisticated and expensive irradiation sources.

A near-infrared frequency upconversion fluorescent probe for rapid and sensitive visual detection of sulfur dioxide.

Inflammation is a complex physiological response involving various cellular and molecular events. Sulfur dioxide (SO2), which is usually in the form of HSO3- and SO32- under physiological conditions, plays a crucial role in the regulation of inflammation and diseases. Frequency upconversion luminescence (FUCL) can realize the unique anti-Stokes process of long-wavelength excitation to short-wavelength emission; thus, it is a highly promising optical method for in vivo imaging due to its deep tissue penetration, low photo-damage, etc. Therefore, we developed a near-infrared FUCL NIRX-1 probe for the detection of HSO3-. NIRX-1 had a fast response (80 s), a low detection limit (0.43 μM), and high selectivity towards HSO3-. In addition, NIRX-1 had deep light penetration ability due to the near-infrared excitation at 808 nm and was able to detect HSO3- in living cells and mice. Lastly, NIRX-1 was employed in the imaging of HSO3- in an inflammation mouse model through FUCL imaging techniques. All these features make NIRX-1 a good candidate for the investigation of SO2-associated physiological and pathological processes.

Effect of annealing on the room temperature luminescence of coumarin 106 in PVA films

We studied the effect of annealing on the luminescence of Coumarin 106 (C106) in poly (vinyl alcohol) films (PVA films). The samples and reference polymer films were treated at temperatures between 100 °C and 150 °C (212 F and 302 F) for various times. After cooling and smoothing, the samples and references were measured at room temperature. We observed that the PVA polymer (reference films) changes its optical properties with annealing at higher temperatures, affecting the baselines in absorption and the backgrounds in emission measurements. This requires precise background subtractions and control of the signal-to-noise ratio. Whereas the fluorescence intensity of C106 in PVA films modestly decreases with annealing, the phosphorescence depends dramatically and progressively increases by many folds. The fluorescence quantum yields and lifetimes decrease with the annealing, which suggests an increase in the non-radiative processes in the singlet excited state S1. The increase in the phosphorescence intensities results from increased intersystem crossing (ISC), which also decreases fluorescence. We also studied the effect of annealing on phosphorescence with the directly excited triplet state of C106. In this case, two processes are affected by annealing, S0→T1 absorption and T1→S0 phosphorescence. The long-wavelength excitation (475 nm) avoids PVA polymer excitation. The phosphorescence lifetime decreases with annealing while the phosphorescence intensity increases. These changes suggest that the radiative rate of T1 → S0 increases with annealing.

FRET-based two-photon benzo[a] phenothiazinium photosensitizer for fluorescence imaging-guided photodynamic therapy

To overcome the conflict between the long-wavelength excitation and high singlet oxygen quantum yield of photosensitizers, we conjugated a two-photon fluorophore, tetrahydroquinoxaline coumarin (TQ), and an efficient photodynamic therapeutic agent, benzo[a]phenothiazinium (NBS-NH2), through a hexamethylene linker to build a two-photon photosensitizer, TQ-NBS. In TQ-NBS, TQ served as an energy donor and NBS-NH2 acted as an energy acceptor; and TQ-NBS was a Förster resonance energy transfer (FRET) cassette with a 92.8% efficiency. The large two-photon absorption cross-section of TQ allowed photosensitizer TQ-NBS to work in a 900 nm two-photon excitation (TPE) mode, which greatly benefited the deep tissue penetration in PDT treatment. Meanwhile, the excellent phototoxicity and near-infrared fluorescence of NBS-NH2 was kept in TQ-NBS under a TPE mode via a FRET process. Photosensitizer TQ-NBS exhibited a high phototoxic efficacy in living cells and tumor-bearing mice.

3D printed self-calibrating on-site sensing platform based on bimodal excitation carbon dots for visual 4-nitrophenol detection by means of the localization of inner filter effect and pH regulation

For facile and rapid detection of 4-nitrophenol (4-NP), we synthesize nitrogen-doped carbon dots (N-CDs) through microwave radiation treatment using melamine and o-phenylenediamine as precursors. We employed N-CDs as an ingenious ratiometric fluorescence sensor via a novel bimodal excitation behavior. As the concentration of N-CDs increases, the broad excitation peak splits into two excitation peaks. The blue-shift phenomenon appears at the short-wavelength excitation peak, while the long-wavelength excitation peak presents the red-shift. Consequently, 4-NP can be sensitively detected by N-CDs owing to the localization of inner filter effect (L-IFE) with the detection limit of 83 nM ranging from 0.083 to 80 µM. Moreover, a self-calibrating on-site sensing platform constructed by 3D printing technique realizes the visual 4-NP detection in actual samples based on bimodal excitation behavior and RGB analysis. Our work not only presents a novel perspective for visual 4-NP sensing, but also renders the integration of 3D printing technology and the CDs industry.

Bright NIR-Emitting Styryl Pyridinium Dyes with Large Stokes' Shift for Sensing Applications.

Two NIR-emitting donor-π-acceptor (D-π-A) type regioisomeric styryl pyridinium dyes (1a-1b) were synthesized and studied for their photophysical performance and environment sensitivity. The two regioisomers, 1a and 1b, exhibited interesting photophysical properties including, longer wavelength excitation (λex ≈ 530-560 nm), bright near-infrared emission (λem ≈ 690-720 nm), high-fluorescence quantum yields (ϕfl ≈ 0.24-0.72) large Stokes' shift (∆λ ≈ 150-240 nm) and high-environmental sensitivity. Probe's photophysical properties were studied in different environmental conditions such as polarity, viscosity, temperature, and concentration. Probes (1a-1b) exhibited noticeable changes in absorbance, emission and Stokes' shift while responding to the changes in physical environment. Probe 1b exhibited a significant bathochromic shift in optical spectra (∆λ ≈ 20-40 nm) compared to its isomer 1a, due to the regio-effect. Probes (1a-1b) exhibited an excellent ability to visualize bacteria (Bacillus megaterium, Escherichia coli), and yeast (Saccharomyces cerevisiae) via fluorescence microscopy.