Deep blue emitting dual state fluorescent triphenylamine-dicyclohexylurea derivative: Multi-stimuli responsive fluorescence switching and methanol/water sensing

A new deep blue emissive organic fluorophore (N-cyclohexyl-N-(cyclohexylcarbamoyl)-4-(diphenylamino)benzamide (NCDPB)) was designed and synthesized, which showed strong fluorescence both in solution and solid-state. Solid-state structural analysis of NCDPB revealed non-planar twisted molecular conformation with extended hydrogen bonding between the amide functionalities. The propeller shaped triphenylamine (TPA) and non-planar cyclohexyl unit prevented close π…π stacking and produced strong deep blue emission in the solid state (λmax = 400 nm, quantum yield (Φf) = 12.6 %). NCDPB also exhibited strong solvent polarity dependent tunable emission in solution (λmax = 402-462 nm, Φf = 1.15 (compared to quinine sulphate)). NCDPB showed reversible fluorescence switching between two fluorescence states upon mechanical crushing and heating/solvent exposure. Mechanical crushing caused red shifting of fluorescence from 400 to 447 nm and heating/solvent exposure reversed the fluorescence. Further, NCDPB also displayed off-on reversible/self-reversible fluorescence switching upon exposure to trifluoracetic acid (TFA) and NH3. The repeated fluorescence switching cycles indicated high reversibility without any significant change of fluorescence intensity. The drastically different fluorescence of NCDPB in CH3OH and EtOH was utilized to distinguish them and monitor CH3OH contamination in ethanol and benzene. It showed limit of detection (LOD) of methanol up to 0.25 % and 7 % in benzene and ethanol, respectively. The water sensitive fluorescence modulation of NCDPB in organic solvents was used to sensing water contamination in common organic solvents. Thus, integration of twisted TPA with H-bonding urea produced dual state emitting organic fluorophore with multi-responsive fluorescence switching and solvent sensing.

A new class of teraryl-based AIEgen for highly selective imaging of intracellular lipid droplets and its detection in advanced-stage human cervical cancer tissues

Lipid droplets (LDs) have drawn much attention in recent years. They serve as the energy reservoir of cells and also play an important role in numerous physiological processes. Furthermore, LDs are found to be associated with several pathological conditions, including cancer and diabetes mellitus. Herein, we report a new class of teraryl-based donor-acceptor-appended aggregation-induced emission luminogen (AIEgen), 6a, for selective staining of intracellular LDs in in vitro live 3T3-L1 preadipocytes and the HeLa cancer cell line. In addition, AIEgen 6a was found to be capable of staining and quantifying the LD accumulation in the tissue sections of advanced-stage human cervical cancer patients. Unlike commercial LD staining dyes Nile Red, BODIPY and LipidTOX, AIEgen 6a showed a high Stokes shift (195 nm), a good fluorescence lifetime decay of 12.7 ns, and LD staining persisting for nearly two weeks.

Ionic Rigid Organic Dual-State Emission Compound With Rod-Shaped and Conjugated Structure for Sensitive Al3+ Detection

Dual-state emission (DSE) luminogens, a type of luminescent material which can effectively emit light in both dilute solution and solid states, have attracted tremendous attention, due to their widespread applications in chemical sensing, biological imaging, organic electronic devices, and so on. They overcome the shortcomings of aggregation-induced emission (AIE)-type compounds that do not emit light in dilute solutions and aggregation-caused quenching (ACQ)-type compounds that do not emit light in a concentrated or aggregated state. This work reports a novel ionic DSE material based on rigid rod-shaped organic conjugated structure using 4,4′-bis(2-sulfonatostyryl) biphenyl disodium salt (BSBDS); the ion repulsion effect can reduce the strong π–π interaction in aggregation and achieve high-efficiency luminescence in solution and solid states. In addition to excellent DSE characteristics, BSBDS also exhibits a mechanochromic nature and sensitive detection performance for aluminum ion (Al³⁺).

C-H⋯S hydrogen bonding interactions

The short C-H⋯S contacts found in available structural data for both small molecules and larger biomolecular systems suggest that such contacts are an often overlooked yet important stabilizing interaction. Moreover, many of these short C-H⋯S contacts meet the definition of a hydrogen bonding interaction. Using available structural data from the Cambridge Structural Database (CSD), as well as selected examples from the literature in which important C-H⋯S contacts may have been overlooked, we highlight the generality of C-H⋯S hydrogen bonding as an important stabilizing interaction. To uncover and establish the generality of these interactions, we compare C-H⋯S contacts with other traditional hydrogen bond donors and acceptors as well as investigate how coordination number and metal bonding affect the preferred geometry of interactions in the solid state. This work establishes that the C-H⋯S bond meets the definition of a hydrogen bond and serves as a guide to identify C-H⋯S hydrogen bonds in diverse systems.

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.

Bridged Aromatic Oxo- and Thioethers with Intense Emission in Solution and the Solid State

In this contribution, we report on a class of emitters based on bridged oxo- and/or thioethers revealing striking photoluminescence properties in fluid solution and in the solid state. In total, nine compounds were investigated concerning their photophysical properties, which were interpreted by quantum chemical calculations. To our delight, we discovered compounds possessing nearly identical photoluminescence quantum yields (ΦF ) in solution and in the solid state, which has been rarely reported so far. Besides these efforts, we shed light on the influence of polymorphism and solvent polarity on the emission properties. In addition, an in-depth X-ray diffractometric analysis was conducted to correlate molecular packing in the crystal with differences in the photophysical properties.

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.

A 4-N,N-dimethylaminoaniline salicylaldehyde Schiff-base solution-solid dual emissive fluorophore: An aggregation-induced turquoise emission characteristics in liquid as a fluorescent probe for Zn2+ response; a strong near-infrared emission in solid state and application for optical data storage

A new Schiff-base 1 based on 4-N,N-dimethylaminoaniline salicylaldehyde is developed. It possesses unique solution-solid dual emission behaviour with emission color: an aggregation-induced bright turquoise emission in liquid and strong near-infrared emission in the solid state. Interestingly, on the one hand, compound 1 is promising a ratiometric fluorescent probe for Zn²⁺ ions detection in the aqueous solution with high sensitivity, selectivity, and relatively low detection limit. On the other hand, based on its inner stimuli-responsive nature, outstanding thermostability and photostability, 1 should be a very promising candidate for the write-once read-many optical data storage medium.

Rational Design of Dual-State Emission Luminogens with Solvatochromism by Combining a Partially Shared Donor-Acceptor Pattern and Twisted Structures

We report a general design strategy for a new class of luminogens with dual-state emission (DSEgens) that are brightly emissive in both the solution and solid state, with solvatochromism properties, by constructing a partially shared donor-acceptor pattern based on a twisted molecule. The DSEgens with bright fluorescence emission in both the solid and solution state demonstrate a unique solvatochromism behaviour depending on solvent polarity and thus may have applications in anti-counterfeiting.

Synthesis of Solution-Processable Donor-Acceptor Pyranone Dyads for White Organic Light-Emitting Devices

A series of donor-acceptor pyranones (3a-m, 4a-h) were synthesized using α-oxo-ketene- S, S-acetal as the synthon for their application as emissive materials for energy-saving organic light-emitting devices (OLEDs). Among them, five pyranones 3f, 3g, 3h, 3m, and 4e exhibited highly bright fluorescence in the solid state and weak or no emission in the solution state. Photophysical analysis of these dyes revealed that only 3f and 3m showed aggregation-induced emission behavior in a THF/water mixture (0-99%) with varying water fractions ( f_w) leading to bright fluorescence covering the entire visible region, while other derivatives 3g, 3h, and 4e did not show any fluorescence signal. The computational studies of the compounds revealed that the longer wavelength absorption originates from HOMO to LUMO electronic excitation. These dyes exhibited good thermal stability with 5% weight loss temperature in the range of 218-347 °C. The potential application of the donor-acceptor pyranone dyads was demonstrated by fabrication of solution-processed OLEDs. Remarkably, OLED devices prepared using highly emissive compounds 6-(anthracen-9-yl)-4-(methylthio)-2-oxo-2 H-pyran-3-carbonitrile (3m) and 6-(4-methoxyphenyl)-4-(methylthio)-2-oxo-2 H-pyran-3-carbonitrile (3f) displayed pure white emission with CIE coordinates of (0.29, 0.31) and (0.32, 0.32), respectively. Additionally, the resultant devices exhibited external quantum efficiencies of 1.9 and 1.2% at 100 cd m^-2, respectively.

Intramolecular Electrophilic Cyclization Approach to 6-Substituted Naphtho[2,1- b]benzofurans: Novel Dual-State Emissive Fluorophores with Blue Emission

A regiospecific synthesis of naphtho[2,1- b]benzofurans with a substituent at the C6 position was achieved via intramolecular 6-endo-dig electrophilic cyclization under acidic conditions to construct the central aromatic C ring. Screening of the synthesized compounds using a high-content imaging system enabled us to discover novel dual state emissive compounds 2{ 1,6}, 2{ 1,8}, and 2{ 4,3}, which are highly emissive with blue emission in their solid states as well as in solution states in most solvents. In addition, the compounds 2{ 4,3}, 2{ 4,12}, and 2{ 5,13} were found to be the most cell permeable in HeLa cells for live cell imaging with negligible phototoxicity.

Methods for the synthesis of annulated pyrroles via cyclisation strategies

In this report, we review the methods that have been employed to synthesise annulated pyrroles.