Experimental and theoretical comprehension of ESIPT fluorophores based on a 2-(2'-hydroxyphenyl)-3,3'-dimethylindole (HDMI) scaffold

Excited-State Intramolecular Proton Transfer (ESIPT) emission is associated with intense single or multiple fluorescence in the solid-state, along with enhanced photostability and sensitivity to the close environment. As a result, ESIPT probes are attractive candidates for ratiometric sensing of a variety of substrates. A new family of ESIPT fluorophores is described herein, inspired by the well-known 2-(2'hydroxyphenyl)benzazole (HBX) organic scaffold. The connection of 3,3'-dimethylindole (or 3H-indole) derivatives with phenol rings triggers the formation of novel 2-(2'-hydroxyphenyl)-3,3'-dimethylindole (HDMI) fluorophores, capable of stimuli-responsive ESIPT emission. This brand new family of dyes displays redshifted emission, as compared to HBX, along with an unprecedented acid/base-mediated stabilization of different rotamers, owing to supramolecular interactions with methyl groups. These compounds are therefore highly sensitive to external stimuli, such as the presence of acid or base, where protonated and deprotonated species have specific optical signatures. Moreover, a new pyridine-functionalized HDMI dye displays acid-sensitive AIE properties. The photophysical properties of all compounds have also been studied using ab initio calculations to support experiments in deciphering the nature of the various radiative transitions observed and the related excited rotameric species.

Difluoro Dipyridomethene Boron Complexes: Synthesis, Characterization, and Ab Initio Calculations

Molecular engineering studies on the meso-cyano difluoro dipyridomethene boron complexes are presented and two series (a and b) of novel fluorophores are extensively studied. Halogenated derivatives were reacted under Suzuki-Miyaura or Sonogashira cross coupling reactions to introduce electron-donating or electron-withdrawing functional groups on positions 1 and 2 of the aromatic ligand. All derivatives were obtained in 14-90% yields and studied in detail by structural, photophysical, and computational analyses. Both series display excellent emissive properties in solution with blue to orange fluorescence emission upon blue light absorption and promising features as solid emitters. All the spectroscopic measurements are supported and confirmed by first-principles theoretical calculations combining TD-DFT and CC2. Series b, featuring an aryl substituent onto position 1 of the aromatic core, showed significantly large Stokes shifts values.

Styrylpyrimidine chromophores with bulky electron-donating substituents: experimental and theoretical investigation

Styrylpyrimidines with bulky 9,9-dimethylacridan, phenoxazine and phenothiazine electron-donating fragments were designed. Thermally activated delayed fluorescence (TADF) properties were expected for these structures. These chromophores exhibit peculiar emission properties. For 9,9-dimethylacridan and phenoxazine derivatives, a single emission highly sensitive to the polarity is observed in solution whereas for phenothiazine derivative a dual emission is observed in solution and is attributed to the coexistence of quasi-axial (Qax) and quasi-equatorial (Qeq) conformers. This study intends to understand through theoretical and experimental works, why the studied chromophores do not exhibit TADF properties, contrary to what was expected. The absence of phosphorescence both at room temperature and 77 K tends to indicate the impossibility to harvest triplet states in these systems. Wave-function based calculations show that for both conformers of the three chromophores the S1-T1 splitting is significantly larger than 0.2 eV. The second triplet state T2 of Qeq conformers is found very close in energy to the singlet S1 state, but S1 and T2 states possess similar charge transfer characters. This prevents efficient spin-orbit coupling between the states, which is consistent with the absence of TADF.

Interplay between Dual-State and Aggregation-Induced Emission with ESIPT Scaffolds Containing Triphenylamine Substituents: Experimental and Theoretical Studies

We detail the synthesis of a series of fluorophores containing triphenylamine derivatives along with their photophysical, electrochemical, and electronic structure properties. These compounds include molecular structures derived from imino-phenol (anil) and hydroxybenzoxazole scaffolds originating from similar salicylaldehyde derivatives and display excited-state intramolecular proton transfer. We show that depending on the nature of the π-conjugated scaffold, different photophysical processes are observed: aggregation-induced emission or dual-state emission, with a modulation of the fluorescence color and redox properties. The photophysical properties are further rationalized with the help of ab initio calculations.

Solid-state emitters presenting a modular excited-state proton transfer (ESIPT) process: recent advances in dual-state emission and lasing applications

This review aims at providing a broad readership of material and physical chemists, as well as those interested in ab initio calculations, about recent advances in the fields of dual solution-solid emitters and lasing applications based on organic dyes displaying an excited-state intramolecular proton transfer (ESIPT) process. ESIPT is known to be highly sensitive to the immediate environment leading to the engineering of a wide range of stimuli-responsive fluorescent dyes. With the structural diversity of ESIPT-capable fluorophores being large, many applications have been targeted over the years in the fields of optoelectronics, biology and luminescent displays. This review wishes to point out two emerging applications concerning ESIPT fluorophores, which are the answer for the quest for emitters fluorescing both in solution and in the solid state, and those capable of light amplification.

Heteroaryl-Substituted Bis-Anils: Aggregation-Induced Emission (AIE) Derivatives with Tunable ESIPT Emission Color and pH Sensitivity

The two-step synthesis, structural, and photophysical properties of a series of heteroaryl-substituted bis-anil derivatives presenting aggregation-induced emission (AIE) coupled with an excited-state intramolecular proton transfer (ESIPT) process is described. The fluorescence color of the aggregates can be fine tuned by changing the electronic nature of the peripheral substitution, leading to a wide range of emission wavelengths (from green to the near infra-red). Moreover, upon introduction of strong electron-withdrawing groups such as cyano (CN), a competition between ESIPT and deprotonation is observed leading to the emission of the anionic species at low water percentage. This observation led to the synthesis of an additional mixed AIE fluorophore, functionalized by methoxy groups on one side and cyano groups on the other side. Upon addition of water, this dye displays first anionic emission, followed by typical AIE/ESIPT red fluorescence upon formation of the aggregates. TD-DFT calculations on selected AIE dyes were performed to rationalize the nature of the emissive transitions in these derivatives.

Lysosomes targeting pH activable imaging-guided photodynamic agents

Photodynamic therapy (PDT) is a photochemistry-based medical treatment combining light at a specific wavelength and a photosensitizer (PS) in the presence of oxygen. Application of PDT as a conventional treatment is limited and clearly the approval in clinics of new PS is challenging. The selective accumulation of the PS in the targeted malignant cells is of paramount importance to reduce the side effects that are typical of the current worldwide approved PS. Here we report a new series of aniline- and iodine-substituted BODIPY derivatives (1-3) as promising lysosome-targeting and pH-responsive theranostic PS, which displayed a significant in vitro light-induced cytotoxicity, efficient imaging properties and low dark toxicity (for 2 and 3). These compounds were obtained in few reproducible synthetic steps and good yields. Spectroscopic and electrochemical measurements along with computational calculations confirmed the quenching of the emissive properties of the PS, while both fluorescence and 1O2 emission were obtained only under acidic conditions inducing amine protonation. The pKa values and pH-dependent emissive properties of 1-3 being established, their cellular uptake and activation in the lysosomal vesicles (pH ≈ 4-5) were confirmed by their co-localization with the commercial LysoTracker deep red and light-induced cytotoxicity (IC50 between 0.16 and 0.06 µM) against HeLa cancer cells.

Color-Tunable Multifunctional Excited-State Intramolecular Proton Transfer Emitter: Stimulated Emission of a Single Dye

The excited-state intramolecular proton transfer chromophores were regarded as good materials for laser action generation due to their inherent four-level photocycle. The excitation-dependent properties of these compounds enable light amplification from two distinct forms: both enol and keto, making it possible to obtain dual fluorescence emission. Herein, we report that a third option is possible for the first time stimulated emission was realized with a deprotonated ESIPT molecule based on a novel rigidified 2-(2'-hydroxyphenyl)benzothiazole derivative, triggering the possibility to fabricate real-time tunable active material. Through the rational engineering of the ratio of each emissive species, a red-green-blue device was fabricated with the possibility of white light generation. The degenerated two-wave mixing setup was applied to construct a continuously tunable distributed feedback laser.

Synthesis and Optical Properties of Excited-State Intramolecular Proton Transfer (ESIPT) Emitters with Sulfobetaine Fragments

This article describes the synthetic efforts towards the solubilization of organic fluorescent emitters based on a 2-(2'-hydroxybenzofuranyl)benzazole (HBBX) scaffold in aqueous media under physiological conditions (PBS, pH 7.4). These dyes are well-known to display the excited-state intramolecular proton transfer (ESIPT) process which leads to a Stokes-shifted fluorescence with enhanced photostability and strong environment dependent features. Organic dyes are hydrophobic by nature and their vectorization into aqueous media usually necessitates amphiphilic polymers. In this study, we show that the incorporation of one or two sulfobetaine fragments, a highly biocompatible zwitterionic unit leads to the vectorization in buffer solution at pH 7.4 while keeping a reasonable ESIPT fluorescence emission. The photophysical properties of all dyes were studied in multiple solvents and showed that, depending on structure and environment, different excited-state species are observed: normal or tautomeric species, as well as a competitive anionic fluorescent derivative. This study shows that it is not only possible to solubilize fluorescent ESIPT dyes in water using sulfobetaine(s) but also that the optical properties can be finely tuned depending on small structural inputs.

Excited-State Intramolecular Proton Transfer Dyes with Dual-State Emission Properties: Concept, Examples and Applications

Dual-state emissive (DSE) fluorophores are organic dyes displaying fluorescence emission both in dilute and concentrated solution and in the solid-state, as amorphous, single crystal, polycrystalline samples or thin films. This comes in contrast to the vast majority of organic fluorescent dyes which typically show intense fluorescence in solution but are quenched in concentrated media and in the solid-state owing to π-stacking interactions; a well-known phenomenon called aggregation-caused quenching (ACQ). On the contrary, molecular rotors with a significant number of free rotations have been engineered to show quenched emission in solution but strong fluorescence in the aggregated-state thanks to restriction of the intramolecular motions. This is the concept of aggregation-induced emission (AIE). DSE fluorophores have been far less explored despite the fact that they are at the crossroad of ACQ and AIE phenomena and allow targeting applications both in solution (bio-conjugation, sensing, imaging) and solid-state (organic electronics, data encryption, lasing, luminescent displays). Excited-State Intramolecular Proton Transfer (ESIPT) fluorescence is particularly suitable to engineer DSE dyes. Indeed, ESIPT fluorescence, which relies on a phototautomerism between normal and tautomeric species, is characterized by a strong emission in the solid-state along with a large Stokes’ shift, an enhanced photostability and a strong sensitivity to the close environment, a feature prone to be used in bio-sensing. A drawback that needs to be overcome is their weak emission intensity in solution, owing to detrimental molecular motions in the excited-state. Several strategies have been proposed in that regard. In the past few years, a growing number of examples of DSE-ESIPT dyes have indeed emerged in the literature, enriching the database of such attractive dyes. This review aims at a brief but concise overview on the exploitation of ESIPT luminescence for the optimization of DSE dyes properties. In that perspective, a synergistic approach between organic synthesis, fluorescence spectroscopy and ab initio calculations has proven to be an efficient tool for the construction and optimization of DSE-ESIPT fluorophores.

Blue-Emitting 2-(2'-Hydroxyphenyl)benzazole Fluorophores by Modulation of Excited-State Intramolecular Proton Transfer: Spectroscopic Studies and Theoretical Calculations

This article describes the synthesis, spectroscopic studies, and theoretical calculations of nine original fluorophores based on the 2-(2'-hydroxyphenyl)benzazole (HBX) scaffold, functionalized at the 4-position of the phenol ring by ethynyl-extended aniline moieties. HBX dyes are well-known to display an excited-state intramolecular proton transfer (ESIPT) process, owing to a strong six-membered hydrogen bond in their structure that allows for an enol/keto tautomerism after photoexcitation. Appropriate electronic substitution can perturb the ESIPT process, leading to dual fluorescence, both excited tautomers emitting at specific wavelengths. In the examples described herein, it is demonstrated that the proton transfer can be finely frustrated by a modification of the constitutive heteroring, leading to a single emission band from the excited enol or keto tautomer or a dual emission with relative intensities highly dependent on the environment. Moreover, the nature of the functionalization of the N-alkylated aniline moiety also has a significant importance on the relative excited-state stabilities of the two tautomers in solution. To shed more light on these features, quantum chemical calculations by the density functional theory are used to determine the excited-state energies and rationalize the experimental spectroscopic data.

Dual Solution-/Solid-State Emissive Excited-State Intramolecular Proton Transfer (ESIPT) Dyes: A Combined Experimental and Theoretical Approach

Excited-state intramolecular proton transfer (ESIPT) dyes typically show strong solid-state emission, but faint fluorescence intensity is observed in the solution state owing to detrimental molecular motions. This article investigates the influence of direct (hetero)arylation on the optical properties of 2-(2'-hydroxyphenyl)benzoxazole ESIPT emitters. The synthesis of two series of ESIPT emitters bearing substituted neutral or charged aryl, thiophene, or pyridine rings is reported herein along with full photophysical studies in solution and solid states, demonstrating the dual solution-/solid-state emission behavior. Depending on the nature of substitution, several excited-state dynamics are observed: quantitative or partially frustrated ESIPT process or deprotonation of the excited species. Protonation studies revealed that pyridine substitution triggered a strong increase of quantum yield in the solution state for the protonated species owing to favorable quinoidal stabilization. These attractive features led to the development of a second series of dyes with alkyl or aryl pyridinium moieties showing strong tunable solution/solid fluorescence intensity. For each series, ab initio calculations helped rationalize and ascertain their behavior in the excited state and the nature of the emission observed by the experimental results.

Ultra-Narrow-Band NIR Photomultiplication Organic Photodetectors Based on Charge Injection Narrowing

Ultra-narrow-band NIR photomultiplication organic photodetectors (PM-OPDs) were realized in ITO/PEDOT:PSS/active layers/Al based on an interfacial-trap-induced charge injection narrowing (CIN) concept. The rather less Bod Ethex-Hex (BEH) is imbedded in a polymer donor matrix to form large amounts of isolated electron traps. Trapped electrons in BEH close to an Al electrode will enforce hole-tunneling injection induced by interfacial band bending, resulting in a photomultiplication phenomenon. PM-OPDs with P3HT:BEH as the active layer exhibit a narrow response peak at 850 nm with a full-width at half-maximum (fwhm) of 27 nm as well as a rather weak response from 650 to 800 nm. The EQE of 29 700% at 850 nm was achieved in PM-OPDs by incorporating 0.02 wt % of F₆TCNNQ under -13 V of applied voltage. The rejection ratio (RR) of the optimized PM-OPDs with F₆TCNNQ is 11 for EQE_850 nm/EQE_700 nm and 10 for EQE_850 nm/EQE_750 nm, respectively. An EQE of 15 300% at 850 nm was achieved in the ternary PM-OPDs under -13 V of applied voltage, with markedly enhanced RRs of 44 for EQE_850 nm/EQE_700 nm and 30 for EQE_850 nm/EQE_750 nm.

Interprofessional collaboration among sport science and sports medicine professionals: an international cross-sectional survey

As in other areas of healthcare, the quality of patient care in the field of sport science and sports medicine (SSSM) could benefit from interprofessional collaboration between the professions involved. As a prerequisite, healthcare providers in the SSSM field should be equipped with positive attitudes and perceptions toward interprofessional collaboration (IPC) and interprofessional education (IPE), however detailed investigations are lacking. This study aimed to collect and compare socio-demographic data as well as interprofessional attitudes of SSSM professionals from an international perspective. Subjects were invited via professional SSSM organizations, personal networks and social media to participate in a cross-sectional online survey. Three-hundred and twenty complete datasets of SSSM professionals from the regions USA (n = 83), Canada (n = 179) and Europe (n = 58) were evaluated. In this survey, socio-demographic data as well as attitudes toward IPC and IPE using the 4 subscales of the University of West of England interprofessional Questionnaire (UWE-IP) were collected and analyzed with descriptive and inferential statistics. In the socio-demographic data, there was a diversity of participants representing different regional healthcare, sports and educational framing conditions. On average, in all regions clear positive attitudes were shown in the UWE-IP subscales communication & teamwork, interprofessional learning and interprofessional relationship, whereas in the subscale interprofessional interaction negative perceptions were observed on average across all regions. Significant effects of participants' demographic variables region, age and gender on some of the subscales were detected. Practitioners in the SSSM field have a high willingness and a beneficial preparedness for IPC and IPE, however, the framing conditions and the systems the respondents surveyed are working in do not support IPC. Interprofessional settings in learning and in workplace (e.g., theme-centred workshops, patient-centred case studies, health promotion activities) may help to improve interprofessional interactions in SSSM.

Impact of Heteroatom Substitution on Dual-State Emissive Rigidified 2-(2'-hydroxyphenyl)benzazole Dyes: Towards Ultra-Bright ESIPT Fluorophores*

2-(2'-Hydroxyphenyl)benzazole (HBX) fluorophores are well-known excited-state intramolecular proton transfer (ESIPT) emitters largely studied for their synthetic versatility, photostability, strong solid-state fluorescence and ability to engineer dual emission, thus paving the way to applications as white emitters, ratiometric sensors, and cryptographic dyes. However, they are heavily quenched in solution, due to efficient non-radiative pathways taking place as a consequence of the proton transfer in the excited-state. In this contribution, the nature of the heteroring constitutive of these rigidified HBX dyes was modified and we demonstrate that this simple structural modification triggers major optical changes in terms of emission color, dual emission engineering, and importantly, fluorescent quantum yield. Investigation of the photophysical properties in solution and in the solid state of a series of ethynyl-TIPS extended HBX fluorophores, along with ab initio calculations demonstrate the very promising abilities of these dyes to act as bright dual-state emitters, in both solution (even in protic environments) and solid state.

Fluorine-18-Labeled Fluorescent Dyes for Dual-Mode Molecular Imaging

Recent progress realized in the development of optical imaging (OPI) probes and devices has made this technique more and more affordable for imaging studies and fluorescence-guided surgery procedures. However, this imaging modality still suffers from a low depth of penetration, thus limiting its use to shallow tissues or endoscopy-based procedures. In contrast, positron emission tomography (PET) presents a high depth of penetration and the resulting signal is less attenuated, allowing for imaging in-depth tissues. Thus, association of these imaging techniques has the potential to push back the limits of each single modality. Recently, several research groups have been involved in the development of radiolabeled fluorophores with the aim of affording dual-mode PET/OPI probes used in preclinical imaging studies of diverse pathological conditions such as cancer, Alzheimer's disease, or cardiovascular diseases. Among all the available PET-active radionuclides, 18F stands out as the most widely used for clinical imaging thanks to its advantageous characteristics (t1/2 = 109.77 min; 97% β+ emitter). This review focuses on the recent efforts in the synthesis and radiofluorination of fluorescent scaffolds such as 4,4-difluoro-4-bora-diazaindacenes (BODIPYs), cyanines, and xanthene derivatives and their use in preclinical imaging studies using both PET and OPI technologies.

Solitary plasmacytoma of thoracic vertebra in a woman with Lynch syndrome: A case report

INTRODUCTION

One of the major disabling health conditions among elderly is back pain due to degenerative diseases. Less than 1% of spine disorders are caused by malignancies. Among the rare primary vertebral neoplasms the multiple myeloma and the plasmacytoma account for 26% of these cases.

PRESENTATION OF CASE

We are reporting a case of 64 year-old woman, who suffered from progressive upper back pain and intermittent neurological symptoms including lower limb weakness and voiding disorder under axial loading. Her medical history includes a Lynch syndrome (LS). Computed tomography (CT) and magnetic resonance imaging (MRI) detected a single malignant osteolytic process of the spine involving T5. Urgent surgery with laminectomy intralesional tumor removal and posterior stabilization (Th4-Th6) due to unstable pathologic fracture with spinal cord compression was conducted after interdisciplinary decision. Histopathological examination of the tumor revealed a solitary plasmacytoma.

DISCUSSION

To our knowledge this is the first case report of a solitary plasmacytoma of the bone (SPB) that arise in a patient who suffers from LS. Similar DNA mismatch repair malfunction is existent in LS and SPB. Hence, a hereditary correlation might be imaginable.

CONCLUSION

When detecting a lytic spinal tumor in a patient who suffers from LS a SPB should be taken under consideration.

Functional panchromatic BODIPY dyes with near-infrared absorption: design, synthesis, characterization and use in dye-sensitized solar cells

We report two novel functional dyes based on a boron-dipyrromethene (BODIPY) core displaying a panchromatic absorption with an extension to the near-infrared (NIR) range. An innovative synthetic approach for preparing the 2,3,5,6-tetramethyl-BODIPY unit is disclosed, and a versatile way to further functionalize this unit has been developed. The optoelectronic properties of the two dyes were computed by density functional theory modelling (DFT) and characterized through UV–vis spectroscopy and cyclic voltammetry (CV) measurements. Finally, we report preliminary results obtained using these functional dyes as photosensitizers in dye-sensitized solar cells (DSSCs).

Hydrogen Bonding as a Supramolecular Tool for Robust OFET Devices

In the present study, we demonstrated the effect of hydrogen bonding in the semiconducting behaviour of a small molecule used in organic field-effect transistors (OFETs). For this study, the highly soluble dumbbell-shaped molecule, Boc-TATDPP based on a Boc-protected thiophene-diketopyrrolopyrrole (DPP) and triazatruxene (TAT) moieties was used. The two Boc groups of the molecule were removed by annealing at 200 °C, which created a strong hydrogen-bonded network of NH-TATDPP supported by additional π-π stacking. These were characterised by thermogravimetric analysis (TGA), UV/Vis and IR spectroscopy, XRD and high-resolution (HR)-TEM measurements. FETs were fabricated with the semiconducting channel made of Boc-TATDPP and NH-TATDPP separately. It is worth mentioning that the Boc-TATDPP film can be cast from solution and then annealed to get the other systems with NH-TATDPP. More importantly, NH-TATDPP showed significantly higher hole mobilities compared to Boc-TATDPP. Interestingly, the high hole mobility in the case of NH-TATDPP was unaffected upon blending with [6,6]-phenyl-C71-butyric acid methyl ester (PC₇₁ BM). Thus, this robust hydrogen-bonded supramolecular network is likely to be useful in designing efficient and stable organic optoelectronic devices.

Reversible turn-on fluorescent Cu(ii) sensors: rather dream than reality?

Reversible turn-on fluorescent Cu(ii) sensors are of high interest to understand copper metabolism in biology and medicine. However, they are intrinsically difficult to build, and careful studies are needed to exclude Cu(ii)-induced sensor oxidation.

Excited-state intramolecular proton transfer (ESIPT) emitters based on a 2-(2′-hydroxybenzofuranyl)benzoxazole (HBBO) scaffold functionalised with oligo(ethylene glycol) (OEG) chains

This article describes the multi-step synthesis of 2-(2′-hydroxybenzofuran)benzoxazole (HBBO) derivatives functionalised with one to three oligo(ethylene glycol) (OEG) chains with the goal to allow a good vectorization in aqueous media.

Global scaling for semi-quantitative analysis in FP-CIT SPECT

Semi-quantitative characterization of dopamine transporter availability from single photon emission computed tomography (SPECT) with 123I-ioflupane (FP-CIT) is based on uptake ratios relative to a reference region. The aim of this study was to evaluate the whole brain as reference region for semiquantitative analysis of FP-CIT SPECT. The rationale was that this might reduce statistical noise associated with the estimation of non-displaceable FP-CIT uptake. Patients, methods: 150 FP-CIT SPECTs were categorized as neurodegenerative or non-neurode- generative by an expert. Semi-quantitative analysis of specific binding ratios (SBR) was performed with a custom-made tool based on the Statistical Parametric Mapping software package using predefined regions of interest (ROIs) in the anatomical space of the Montreal Neurological Institute. The following reference regions were compared: predefined ROIs for frontal and occipital lobe and whole brain (without striata, thalamus and brainstem). Tracer uptake in the reference region was characterized by the mean, median or 75th percentile of its voxel intensities. The area (AUC) under the receiver operating characteristic curve was used as performance measure. Results: The highest AUC of 0.973 was achieved by the SBR of the putamen with the 75th percentile in the whole brain as reference. The lowest AUC for the putamen SBR of 0.937 was obtained with the mean in the frontal lobe as reference. Conclusion: We recommend the 75th percentile in the whole brain as reference for semi-quantitative analysis in FP-CIT SPECT. This combination provided the best agreement of the semi-quantitative analysis with visual evaluation of the SPECT images by an expert and, therefore, is appropriate to support less experienced physicians.

An extended excited-state intramolecular proton transfer (ESIPT) emitter for random lasing applications

An original ESIPT emitter showing random lasing properties is presented in this article.

Tuning ESIPT fluorophores into dual emitters

Using first-principle approaches, we show how ESIPT can be controlled by fine-tuning of substituents, hence leading to new dual emitters.

Dyes undergoing excited-state intramolecular proton transfer (ESIPT) are known to present large Stokes shifts as a result of the important geometrical reorganisation following photon absorption. When the ESIPT process is not quantitative, one can obtain dual emitters characterised by two distinct fluorescence bands, observed due to emissions from both the canonical and ESIPT isomers. However, dual emission generally requires to maintain a very specific balance, as the relative excited-state free energies of the two tautomers have to be within a narrow window to observe the phenomenon. Consequently, simple chemical intuition is insufficient to optimise dual emission. In the present contribution, we investigate, with the help of quantum-mechanical tools and more precisely, time-dependent density functional theory (TD-DFT) and algebraic diagrammatic construction (ADC), a wide panel of possible ESIPT/dual emitters with various substituents. The selected protocol is first shown to be very robust on a series of structures with known experimental behaviour, and next is applied to novel derivatives with various substituents located at different positions. This work encompasses the largest chemical library of potential ESIPT compounds studied to date. We pinpoint the most promising combinations for building dual emitters, highlight unexpected combination effects and rationalise the impact of the different auxochromes.

2,4 and 2,5-bis(benzooxazol-2′-yl)hydroquinone (DHBO) and their borate complexes: synthesis and optical properties

2,4 and 2,5-bis(benzooxazol-2′-yl)hydroquinone (DHBO) scaffolds show fluorescence stemming from an ESIPT process but also act as chelates toward boron fragments.

Highly fluorescent extended 2-(2′-hydroxyphenyl)benzazole dyes: synthesis, optical properties and first-principle calculations

Restoration of ESIPT upon protonation was demonstrated in an extended-hydroxybenzothiazole derivative in which it was fully inhibited in the neutral state.

Luminescent rhenium(I) tricarbonyl complexes with pyrazolylamidino ligands: photophysical, electrochemical, and computational studies

New pyrazolylamidino complexes fac-[ReCl(CO)3(NH[double bond, length as m-dash]C(Me)pz*-κ(2)N,N)] (pz*H = pyrazole, pzH; 3,5-dimethylpyrazole, dmpzH; indazole, indzH) and fac-[ReBr(CO)3(NH[double bond, length as m-dash]C(Ph)pz*-κ(2)N,N)] are synthesized via base-catalyzed coupling of the appropriate nitrile with pyrazole, or via metathesis by halide abstraction with AgBF4 from a bromido pyrazolylamidino complex and the subsequent addition of LiCl. In order to study both the influence of the substituents present at the pyrazolylamidino ligand, and that of the "sixth" ligand in the complex, photophysical, electrochemical, and computational studies have been carried out on this series and other complexes previously described by us, of the general formula fac-[ReL(CO)3(NH[double bond, length as m-dash]C(R')pz*-κ(2)N,N)](n+) (L = Cl, Br; R' = Me, Ph, n = 0; or L = NCMe, dmpzH, indzH, R' = Me, n = 1). All complexes exhibit phosphorescent decays from a prevalently (3)MLCT excited state with quantum yields (Φ) in the range between 0.007 and 0.039, and long lifetimes (τ∼ 8-1900 ns). The electrochemical study reveals irreversible reduction for all complexes. The oxidation of the neutral complexes was found to be irreversible due to halido-dissociation, whereas the cationic species display a reversible process implying the ReI/ReII couple. Density functional and time-dependent density functional theory (TD-DFT) calculations provide a reasonable trend for the values of emission energies in line with the experimental photophysical data, supporting the (3)MLCT based character of the emissions.