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16 pages, 3103 KiB

Open AccessArticle

Photoluminescence Dependance of 2-Bromo-3-aminobenzo[de]anthracene-7-one on Solvent Polarity for Potential Applications in Color-Tunable Optoelectronics

by Emmanuel Karungani, Elena Kirilova, Liga Avotina, Aleksandrs Puckins, Sergejs Osipovs, Titus Ochodo, Mildred Airo and Francis Otieno

Molecules 2025, 30(13), 2677; https://doi.org/10.3390/molecules30132677 - 20 Jun 2025

Viewed by 396

Abstract

The novel benzanthrone derivative, 2-bromo-3-aminobenzo[de]anthracene-7-one (2-Br-3-NH₂BA), was synthesized and extensively characterized to investigate its photophysical behavior in various solvents. It was prepared through selective bromination of 3-aminobenzanthrone using N-bromosuccinimide in dimethylformamide at −20 °C. Featuring a donor–π–acceptor (D–π–A) structure, [...] Read more.

The novel benzanthrone derivative, 2-bromo-3-aminobenzo[de]anthracene-7-one (2-Br-3-NH₂BA), was synthesized and extensively characterized to investigate its photophysical behavior in various solvents. It was prepared through selective bromination of 3-aminobenzanthrone using N-bromosuccinimide in dimethylformamide at −20 °C. Featuring a donor–π–acceptor (D–π–A) structure, 2-Br-3-NH₂BA exhibits pronounced solvatochromism due to the intramolecular charge transfer (ICT) between the amino donor and the carbonyl acceptor groups. Optical measurements conducted in eight solvents of varying polarity revealed a significant bathochromic shift in both absorption and fluorescence emission, with emission maxima red-shifting by over 110 nm from non-polar to polar environments. Corresponding reductions in the optical band gap energies, as calculated from Tauc plots, further support solvent-induced electronic state modulation. Additionally, quantum yield analysis showed higher fluorescence efficiency in non-polar solvents, while polar solvents induced twisted intramolecular charge transfer (TICT), leading to emission quenching. These findings demonstrate the sensitivity of 2-Br-3-NH₂BA to environmental polarity, making it a promising candidate for color-tunable luminescent applications in optoelectronics and sensing. However, further studies in the solid state are required to validate its applicability in device architectures such as OLEDs. Full article

(This article belongs to the Special Issue Study on Synthesis and Photochemistry of Dyes)

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21 pages, 2646 KiB

Open AccessArticle

BOPAM’s Bright and Dark Excited States: Insight from Structural, Photophysical, and Quantum Chemical Investigations

by Kexin Yu, Thanh Chung Pham, Jianjun Huang, Yixuan Li, Luc Van Meervelt, Mark Van der Auweraer, Daniel Escudero and Wim Dehaen

Molecules 2025, 30(13), 2673; https://doi.org/10.3390/molecules30132673 - 20 Jun 2025

Viewed by 350

Abstract

BOPAM exhibits high fluorescence quantum yields, along with exceptional photostability, rendering it a promising platform for applications as fluorescence sensors. However, the development of BOPAM-based fluorophores with extended emission wavelengths remains limited, and the underlying mechanisms of fluorescence quenching via the population of [...] Read more.

BOPAM exhibits high fluorescence quantum yields, along with exceptional photostability, rendering it a promising platform for applications as fluorescence sensors. However, the development of BOPAM-based fluorophores with extended emission wavelengths remains limited, and the underlying mechanisms of fluorescence quenching via the population of dark twisted intramolecular charge transfer (¹TICT) excited states are not yet fully understood. To address these gaps, we synthesized a series of BOPAM derivatives by incorporating electron-donating groups at the boron atoms and the phenyl rings of the BOPAM core. The introduction of bromide, phenyl, and naphthyl groups preserved the intrinsic locally excited (¹LE) emission of BOPAM. In contrast, the incorporation of diphenylamine (BP-DA) and triphenylamine (BP-TA) moieties resulted in a red-shifted emission, attributed to an enhanced intramolecular charge transfer (ICT) process. Notably, in acetonitrile, BP-DA exhibited weak fluorescence originating from a ¹TICT state, which was populated via the S₂ → ¹TICT transition. Furthermore, the emission observed from BP-TA was associated with a higher-lying excited state, likely the initially populated S₂ state possessing a ¹LE character. These findings not only introduce novel red-emissive BOPAM-based fluorophores, but also offer valuable insights into the role of the S₂ state in governing fluorescence quenching mechanisms in BOPAM derivatives. Full article

(This article belongs to the Special Issue BODIPYs: State of the Art and Future Perspectives)

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13 pages, 5468 KiB

Open AccessArticle

A Bifunctional Fluorescence Probe for the Detection of Hypochlorous Acid and Viscosity in Living Cells and Zebrafish

by Xin Zhang, Yanmei Si, Xinpeng Chen, Xuqing Nie, Yiheng Zhang, Li Lin and Yehao Yan

Molecules 2025, 30(7), 1531; https://doi.org/10.3390/molecules30071531 - 30 Mar 2025

Cited by 1 | Viewed by 552

Abstract

As two significant indicators in the microenvironment, hypochlorous acid and viscosity play important roles in multitudinous physiological metabolic processes. However, it is challenging to determine the dynamic levels of hypochlorous acid and viscosity in living cells and organisms because of the absence of [...] Read more.

As two significant indicators in the microenvironment, hypochlorous acid and viscosity play important roles in multitudinous physiological metabolic processes. However, it is challenging to determine the dynamic levels of hypochlorous acid and viscosity in living cells and organisms because of the absence of effective molecular tools that can simultaneously detect hypochlorous acid and viscosity in organisms. Herein, a molecular design strategy was presented to fabricate a single fluorescence probe that can simultaneously detect hypochlorous acid and viscosity by using two different emission channels. In JXR, TICT-based 4-(2-(5-(dimethylamino)thiophen-2-yl)vinyl)-1-methylpyridin-1-ium-iodide chromophore serves as energy acceptor in the FRET process and sensors for hypochlorous acid and viscosity. JXR showed a large Stokes shift, wide emission peak distance, high photostability, and low toxicity. JXR could detect hypochlorous acid and viscosity rapidly, sensitively, and selectively by emitting different fluorescence signals. Importantly, JXR was successfully applied to track the intracellular hypochlorous acid and viscosity in living cells. Meanwhile, the generation of endogenous hypochlorite in living cells can be observed by using JXR. Full article

(This article belongs to the Special Issue Analytical Chemistry in Asia, 2nd Edition)

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13 pages, 4377 KiB

Open AccessArticle

Random Copolymerization: An Efficient Strategy for Significantly Enhancing Photothermal Performance Through Synergistic Open-Shell Radical and TICT Effects

by Wenjin Xu, Haoran Tan, Yu Li, Xiaorui Ma, Haitao Xu, Dan Zhou, Qing Wan and Ruizhi Lv

Polymers 2025, 17(4), 454; https://doi.org/10.3390/polym17040454 - 9 Feb 2025

Viewed by 984

Abstract

Currently, photothermal (PT) polymers are gaining increasing attention in water evaporation, photocatalysis and photothermal therapy. However, high-performance PT polymers often require conjugated backbones and/or large fused units, which can impede non-radiative decay and lead to suboptimal PT performance. The development of general strategies [...] Read more.

Currently, photothermal (PT) polymers are gaining increasing attention in water evaporation, photocatalysis and photothermal therapy. However, high-performance PT polymers often require conjugated backbones and/or large fused units, which can impede non-radiative decay and lead to suboptimal PT performance. The development of general strategies for preparing high-performance PT polymers remains a significant challenge. In this paper, the high-performance donor–acceptor (D–A) random copolymers, named PBT4T-BBT-x (x = 0, 5, 10, 20 and 100), were fabricated by cross-mixing bithiophene donors with benzothiadiazole (BT) and benzodithiadiazole (BBT) acceptors. Notably, when the ratios of BT and BBT are finely tuned, the polymers exhibit significantly controllable open-shell radical effects and twisted intermolecular charge transfer (TICT) states. The synergistic effects of radicals and TICT states notably enhanced the PT performance of random copolymers. Specifically, when the proper ratios of BBT units are used, the photothermal conversion efficiency (PTCE) is remarkably increased from 21.7% to 58.5%, and the PT temperature obviously increases from 150 °C to 232 °C under 808 nm laser irradiation. Furthermore, the random copolymers exhibit good water evaporation rates. We propose that this strategy provides a valuable synthesis pathway for generating high-performance photothermal therapy and water evaporation materials. Full article

(This article belongs to the Section Smart and Functional Polymers)

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9 pages, 2327 KiB

Open AccessArticle

A Novel Near-Infrared Tricyanofuran-Based Fluorophore Probe for Polarity Detection and LD Imaging

by Zhaojia Hang, Shengmeng Jiang, Zhitong Wu, Jin Gong and Lizhi Zhang

Molecules 2024, 29(21), 5069; https://doi.org/10.3390/molecules29215069 - 26 Oct 2024

Cited by 4 | Viewed by 1171

Abstract

In this paper, LD-TCF, a targeting probe for lipid droplets (LDs) with a near-infrared emission wavelength and large Stokes shift, was fabricated for polarity detection by assembling a donor–π–acceptor (D–π–A) molecule with typical twisted intramolecular charge transfer (TICT) characteristics. Surprisingly, the fluorescence emission [...] Read more.

In this paper, LD-TCF, a targeting probe for lipid droplets (LDs) with a near-infrared emission wavelength and large Stokes shift, was fabricated for polarity detection by assembling a donor–π–acceptor (D–π–A) molecule with typical twisted intramolecular charge transfer (TICT) characteristics. Surprisingly, the fluorescence emission wavelength of the newly constructed probe LD-TCF was stretched to 703 nm, and the Stokes shift was amplified to 126 nm. Furthermore, LD-TCF could specifically answer the change in polarity efficiently and did not experience interference from other biologically active materials. Importantly, LD-TCF exhibited the ability to target lipid droplets, providing valuable insights for the early diagnosis and tracking of pathophysiological processes underlying LD polarity. Full article

(This article belongs to the Special Issue Fluorescent Probes in Biomedical Detection and Imaging)

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15 pages, 3771 KiB

Open AccessArticle

An Acid-Responsive Fluorescent Molecule for Erasable Anti-Counterfeiting

by Jiabao Liu, Xiangyu Gao, Qingyu Niu, Mingyuan Jin, Yijin Wang, Thamraa Alshahrani, He-Lue Sun, Banglin Chen, Zhiqiang Li and Peng Li

Molecules 2024, 29(18), 4335; https://doi.org/10.3390/molecules29184335 - 12 Sep 2024

Cited by 2 | Viewed by 1655

Abstract

A tetraphenylethylene (TPE) derivative, TPEPhDAT, modified by diaminotriazine (DAT), was prepared by successive Suzuki–Miyaura coupling and ring-closing reactions. This compound exhibits aggregation-induced emission enhancement (AIEE) properties in the DMSO/MeOH system, with a fluorescence emission intensity in the aggregated state that is 5-fold higher [...] Read more.

A tetraphenylethylene (TPE) derivative, TPEPhDAT, modified by diaminotriazine (DAT), was prepared by successive Suzuki–Miyaura coupling and ring-closing reactions. This compound exhibits aggregation-induced emission enhancement (AIEE) properties in the DMSO/MeOH system, with a fluorescence emission intensity in the aggregated state that is 5-fold higher than that of its counterpart in a dilute solution. Moreover, the DAT structure of the molecule is a good acceptor of protons; thus, the TPEPhDAT molecule exhibits acid-responsive fluorescence. TPEPhDAT was protonated by trifluoroacetic acid (TFA), leading to fluorescence quenching, which was reversibly restored by treatment with ammonia (on–off switch). Time-dependent density functional theory (TDDFT) computational studies have shown that protonation enhances the electron-withdrawing capacity of the triazine nucleus and reduces the bandgap. The protonated TPEPhDAT conformation became more distorted, and the fluorescence lifetime was attenuated, which may have produced a twisted intramolecular charge transfer (TICT) effect, leading to fluorescence redshift and quenching. MeOH can easily remove the protonated TPEPhDAT, and this acid-induced discoloration and erasable property can be applied in anti-counterfeiting. Full article

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14 pages, 6240 KiB

Open AccessArticle

Multi-Stimuli-Responsive Fluorescent Molecule with AIE and TICT Properties Based on 1,8-Naphthalimide

by Yan Yu, Na Qiang, Zhu Liu, Ming Lu, Yuqiu Shen, Jiao Zou, Jinyu Yang and Guocong Liu

Nanomaterials 2024, 14(15), 1255; https://doi.org/10.3390/nano14151255 - 27 Jul 2024

Cited by 2 | Viewed by 1823

Abstract

A multi-stimuli responsive fluorophore, named NBDNI, was developed by constructing a 1,8-naphthalimide derivative in which a rotatable electron-donating N,N-dimethylaniline group attached to its 4-position. This molecular structure endowed NBDNI with aggregate-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties, enabling remarkable fluorescence [...] Read more.

A multi-stimuli responsive fluorophore, named NBDNI, was developed by constructing a 1,8-naphthalimide derivative in which a rotatable electron-donating N,N-dimethylaniline group attached to its 4-position. This molecular structure endowed NBDNI with aggregate-induced emission (AIE) and twisted intramolecular charge transfer (TICT) properties, enabling remarkable fluorescence changes in response to multiple external stimuli: (i) sensitivity to polarity in various solvent systems and polymer matrix; (ii) significant fluorescence response and excellent linearity towards temperature changes in solution; (iii) distinct switch of fluorescence color upon acid and base treatments; (iv) reversible mechanochromism behavior in the solid state. Moreover, the mechanisms underlying the aforementioned stimuli-responsive phenomena have been proposed based on comprehensive systematic measurements. Furthermore, preliminary applications such as fluorescence thermometry and acid/base test paper have been demonstrated. This research will bring about new opportunities for the development of novel stimuli-responsive luminescent materials. Full article

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13 pages, 3558 KiB

Open AccessArticle

Fluorescence of Half-Twisted 10-Acyl-1-methyltetrahydrobenzoquinolines

by Christopher Abelt, Ian Day, Junkai Zhao and Robert Pike

Molecules 2024, 29(13), 3016; https://doi.org/10.3390/molecules29133016 - 25 Jun 2024

Cited by 1 | Viewed by 1328

Abstract

The steric interference of proximal dialkyl amino and acyl groups at the peri (1,8) positions of naphthalene affects the intramolecular charge transfer fluorescence. Previous studies indicate that acyl and freely rotating dimethyl amino groups twist toward coplanarity with the naphthalene ring in the [...] Read more.

The steric interference of proximal dialkyl amino and acyl groups at the peri (1,8) positions of naphthalene affects the intramolecular charge transfer fluorescence. Previous studies indicate that acyl and freely rotating dimethyl amino groups twist toward coplanarity with the naphthalene ring in the excited state. The present study examines the effect of constraining the amino group in a ring. The photophysical properties of 2,2-dimethyl-1-(1-methyl-1,2,3,4-tetrahydrobenzo[h]quinolin-10-yl)propan-1-one (4), ethyl 1-methyl-1,2,3,4-tetrahydrobenzo[h]quinoline-10-carboxylate (5), and 1-methyl-1,2,3,4-tetrahydrobenzo[h]quinoline-10-carbaldehyde (6) are compared with the dimethyl amino derivatives 2 and 3. Crystal structures of 4–6 show that the amine ring adopts a chair conformation, where the N-methyl group is axial. Computational results suggest that the pyramidal amino group planarizes and twists together with the acyl toward coplanarity in the excited state. The ring structure does not thwart the formation of a planar intramolecular charge transfer (PICT) state. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry and Photocatalysis)

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16 pages, 3737 KiB

Open AccessArticle

Screening the Optimal Probe by Expounding the ESIPT Mechanism and Photophysical Properties in Bis-HBX with Multimodal Substitutions

by Min Yang, Hongyan Mu, Jiaan Gao, Qi Zhen, Xiaonan Wang, Xiaotong Guan, Hui Li and Bo Li

Molecules 2024, 29(11), 2692; https://doi.org/10.3390/molecules29112692 - 6 Jun 2024

Cited by 3 | Viewed by 1442

Abstract

DFT and TD-DFT were used in this article to investigate the effects of different substitutions at multiple sites on the photophysical mechanism of bis-HBX in the gas phase. Four different substitution modes were selected, denoted as A₁ (X=Me, Y=S), A₂ (X=OMe, [...] Read more.

DFT and TD-DFT were used in this article to investigate the effects of different substitutions at multiple sites on the photophysical mechanism of bis-HBX in the gas phase. Four different substitution modes were selected, denoted as A₁ (X=Me, Y=S), A₂ (X=OMe, Y=S), B₁ (X=Me, Y=NH), and C₁ (X=Me, Y=O). The geometric parameters proved that the IHBs enhanced after photoexcitation, which was conducive to promote the ESIPT process. Combining the analysis of the PECs, it was revealed that the bis-HBX molecule underwent the ESIPT process, and the ease of the ESIPT process was in the order of A₁ > A₂> B₁ > C₁. In particular, the TICT process in A₁ and B₁ promoted the occurrence of the ESIPT process. In addition, the IC process was identified, particularly in C₁. Meanwhile, the calculation of fluorescence lifetime and fluorescence rate further confirmed that A₁ was the most effective fluorescent probe molecule. This theoretical research provides an innovative theoretical reference for regulating ESIPT reactions and optimizing fluorescent probe molecules. Full article

(This article belongs to the Special Issue Feature Papers in Computational and Theoretical Chemistry)

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25 pages, 5490 KiB

Open AccessArticle

Cooperativity of ESPT and Aggregation-Induced Emission Effects—An Experimental and Theoretical Analysis of a 1,3,4-Thiadiazole Derivative

by Iwona Budziak-Wieczorek, Dominika Kaczmarczyk, Klaudia Rząd, Mariusz Gagoś, Andrzej Stepulak, Beata Myśliwa-Kurdziel, Dariusz Karcz, Karolina Starzak, Gotard Burdziński, Monika Srebro-Hooper and Arkadiusz Matwijczuk

Int. J. Mol. Sci. 2024, 25(6), 3352; https://doi.org/10.3390/ijms25063352 - 15 Mar 2024

Cited by 7 | Viewed by 1775

Abstract

4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV–vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole [...] Read more.

4-[5-(Naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl]benzene-1,3-diol (NTBD) was extensively studied through stationary UV–vis absorption and fluorescence measurements in various solvents and solvent mixtures and by first-principles quantum chemical calculations. It was observed that while in polar solvents (e.g., methanol) only a single emission band emerged; the analyzed 1,3,4-thiadiazole derivative was capable of producing dual fluorescence signals in low polarity solvents (e.g., n-hexane) and certain solvent mixtures (e.g., methanol/water). As clearly follows from the experimental spectroscopic studies and theoretical modeling, the specific emission characteristic of NTBD is triggered by the effect of enol → keto excited-state intramolecular proton transfer (ESIPT) that in the case of solvent mixture is reinforced by aggregation of thiadiazole molecules. Specifically, the restriction of intramolecular rotation (RIR) due to environmental hindrance suppresses the formation of non-emissive twisted intramolecular charge transfer (TICT) excited keto* states. As a result, this particular thiadiazole derivative is capable of simultaneously producing both ESIPT and aggregation-induced emission (AIE). Full article

(This article belongs to the Special Issue Dual Fluorescence Effects)

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13 pages, 2728 KiB

Open AccessArticle

Twisted 8-Acyl-1-dialkyl-amino-naphthalenes Emit from a Planar Intramolecular Charge Transfer Excited State

by Christopher Abelt and Kirsten Sweigart

Photochem 2024, 4(1), 1-13; https://doi.org/10.3390/photochem4010001 - 4 Jan 2024

Cited by 2 | Viewed by 1518

Abstract

Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (3) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (4) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (5 [...] Read more.

Fluorescence from dialkylamino donor–acyl acceptor substituted 1,8-naphthalene derivatives can occur either from a planar (PICT) or a twisted (TICT) intramolecular charge transfer excited state. The photophysical properties of 8-acetyl-1-(dimethyl-amino)naphthalene (3) and 8-pivaloyl-1-(dimethyl-amino)naphthalene (4) are compared with 1-methyl-2,3-dihydronaphtho[1,8-bc]azepin-4(1H)-one (5). In 3 and 4, both the carbonyl and amino groups are forced to twist out of the plane of the naphthalene ring. In 5, these groups are nearly coplanar with the naphthalene. Neither 3 nor 4 fluoresce as strongly as 5, but all three show similar degrees of solvato-chromism and all are strongly quenched by alcohol solvents. Nitrile 6, 8-cyano-1-(dimethyl-amino)naphthalene, does not show the same degree of solvato-chromism as 3–5, nor is it as affected by alcohols. Calculations corroborate the experimental results, indicating that 3–5 emit from a PICT excited state. Full article

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17 pages, 5042 KiB

Open AccessArticle

Paying Comprehensive Attention to the Temperature-Dependent Dual-Channel Excited-State Intramolecular Proton Transfer Mechanism of Fluorescence Ratio Probe BZ-DAM

by Jiaan Gao, Yifu Zhang, Hongyan Mu, Min Yang, Xiaotong Guan, Guangyong Jin and Hui Li

Int. J. Mol. Sci. 2023, 24(18), 13899; https://doi.org/10.3390/ijms241813899 - 9 Sep 2023

Cited by 8 | Viewed by 1623

Abstract

The mechanism of fluorescence detection of diethyl chlorophosphate (DCP) based on 2-substituted benzothiazole (BZ-DAM) was studied by a theoretical calculation method. It should not be ignored that both the BZ-DAM and the detection product BZ-CHO have two excited-state intramolecular proton transfer (ESIPT) channels. [...] Read more.

The mechanism of fluorescence detection of diethyl chlorophosphate (DCP) based on 2-substituted benzothiazole (BZ-DAM) was studied by a theoretical calculation method. It should not be ignored that both the BZ-DAM and the detection product BZ-CHO have two excited-state intramolecular proton transfer (ESIPT) channels. Density functional theory (DFT) and time-dependent DFT (TDDFT) theory were used to study the photophysical mechanism of two compounds in two channels in (acetonitrile) ACN solvent, and the temperature dependence of the two channels was given. Channel 1 is more likely to exist at low temperatures and channel 2 is more likely to exist at high temperatures. By theoretical analysis of the constructed potential energy curve, the hydrogen bond energy and electron-hole analysis, we confirmed that both molecules undergo ESIPT and intramolecular charge transfer (ICT) processes in channel 1 and ESIPT and twisted intramolecular charge transfer (TICT) coupling processes in channel 2. The formation of product BZ-CHO molecules led to a significant fluorescence blue-shift phenomenon and inhibited the ICT process, which confirmed that BZ-DAM could be used as a fluorescence probe for fluorescence detection. We sincerely hope that this work will not only help to clarify the excited-state dynamics behavior of the BZ-DAM probe but also provide a new idea for designing and optimizing a new chemical dosimeter. Full article

(This article belongs to the Section Biochemistry)

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14 pages, 3976 KiB

Open AccessArticle

Indocyanine Green (ICG) Fluorescence Is Dependent on Monomer with Planar and Twisted Structures and Inhibited by H-Aggregation

by Bonghwan Chon, William Ghann, Jamal Uddin, Bahman Anvari and Vikas Kundra

Int. J. Mol. Sci. 2023, 24(17), 13030; https://doi.org/10.3390/ijms241713030 - 22 Aug 2023

Cited by 23 | Viewed by 3299

Abstract

The optical properties of indocyanine green (ICG) as a near-infrared (NIR) fluorescence dye depend on the nature of the solvent medium and the dye concentration. In the ICG absorption spectra of water, at high concentrations, there were absorption maxima at 700 nm, implying [...] Read more.

The optical properties of indocyanine green (ICG) as a near-infrared (NIR) fluorescence dye depend on the nature of the solvent medium and the dye concentration. In the ICG absorption spectra of water, at high concentrations, there were absorption maxima at 700 nm, implying H-aggregates. With ICG dilution, the main absorption peak was at 780 nm, implying monomers. However, in ethanol, the absorption maximum was 780 nm, and the shapes of the absorption spectra were identical regardless of the ICG concentration, indicating that ICG in ethanol exists only as a monomer without H-aggregates. We found that emission was due to the monomer form and decreased with H-aggregate formation. In the fluorescence spectra, the 820 nm emission band was dominant at low concentrations, whereas at high concentrations, we found that the emission peaks were converted to 880 nm, suggesting a new form via the twisted intramolecular charge transfer (TICT) process of ICG. The NIR fluorescence intensity of ICG in ethanol was approximately 12- and 9-times brighter than in water in the NIR-I and -II regions, respectively. We propose an energy diagram of ICG to describe absorptive and emissive transitions through the ICG structures such as the monomer, H-aggregated, and TICT monomer forms. Full article

(This article belongs to the Section Molecular Biophysics)

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14 pages, 2148 KiB

Open AccessArticle

First Experimental Evidence of Anti-Stokes Laser-Induced Fluorescence Emission in Microdroplets and Microfluidic Systems Driven by Low Thermal Conductivity of Fluorocarbon Carrier Oil

by Zain Hayat and Abdel El Abed

Micromachines 2023, 14(4), 765; https://doi.org/10.3390/mi14040765 - 29 Mar 2023

Cited by 1 | Viewed by 2145

Abstract

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We [...] Read more.

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We developed a broadband highly sensitive optofluidic detection system, which enabled us to show for the first time that Rhodamine-B dye molecules can exhibit standard photoluminescence as well as blue-shifted photoluminescence. We demonstrate that this phenomenon originates from the interaction between the pump laser beam and dye molecules when surrounded by the low thermal conductive fluorocarbon oil, generally used as a carrier medium in droplet microfluidics. We also show that when the temperature is increased, both Stokes and anti-Stokes fluorescence intensities remain practically constant until a temperature transition is reached, above which the fluorescence intensity starts to decrease linearly with a thermal sensitivity of about

- 0.4 % / °

C for Stokes emission or

- 0.2 % / °

C for anti-Stokes emission. For an excitation power of 3.5 mW, the temperature transition was found to be about 25

°

C, whereas for a smaller excitation power (0.5 mW), the transition temperature was found to be about 36

°

C. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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49 pages, 23991 KiB

Open AccessEditor’s ChoiceReview

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

by Nikolai I. Georgiev, Ventsislav V. Bakov, Kameliya K. Anichina and Vladimir B. Bojinov

Pharmaceuticals 2023, 16(3), 381; https://doi.org/10.3390/ph16030381 - 1 Mar 2023

Cited by 56 | Viewed by 12596

Abstract

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical [...] Read more.

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery. Full article

(This article belongs to the Special Issue Fluorescence Approaches in Drug Delivery)

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