Low-Molecular-Weight J-Aggregate Solid Red Emitter for Selective and Quantitative Detection of Cyanide.

A dimethylaniline (donor)-indanedione (acceptor) conjugate (sensor 1) with a very low molecular weight of 277 g mol-1 and intramolecular charge transfer (ICT) characteristics was synthesized. Sensor 1 shows weak ICT fluorescence in solution, but strong emission (Φ=16%) in the solid state owing to intramolecular and intermolecular C-H⋅⋅⋅O hydrogen bonds that inhibit the free rotation of the exocyclic C-C single bond. Compared to yellow emitter 1Y, which has a similar donor-acceptor structure, sensor 1 shows red fluorescence in the solid state owing to J-aggregate formation. The colorimetric and fluorometric responses of sensor 1 to cyanide in both solution and solid state are due to the nucleophilic addition of cyanide to the ß-conjugated carbon of the indanedione group, which prohibits ICT. Additionally, inexpensive portable paper-based test kits based on sensor 1 were easily prepared and could be used for fast and quantitative naked-eye cyanide detection in real time.

Intramolecular C-H⋠⋠⋠O Hydrogen-Bonded Solid Emitter as Colorimetric and Fluorometric Cyanide-Selective Chemodosimeter.

An indole-indanedione-based small molecule, compound 1Me, comprising an intramolecular C-H⋅⋅⋅O hydrogen-bond (H-bond) and with an intramolecular charge transfer (ICT) characteristic was prepared for the colorimetric and fluorometric detection of CN- . Compound 1Me is virtually nonfluorescent in solution but emits a strong yellow fluorescence in the solid state because of the intramolecular C-H⋅⋅⋅O H-bond, which inhibits the free rotation of the exocyclic C-C single bond of 1Me. The nucleophilic addition of CN- to the ß-conjugated carbon of the indanedione group of 1Me, which breaks the intramolecular C-H⋅⋅⋅O H-bond and blocks ICT, causes the colorimetric and fluorometric responses of 1Me to CN- . Furthermore, inexpensive and portable paper-based test kits containing 1Me could be used to rapidly and conveniently sense CN- using the naked eye in real time. The results provide a new strategy for designing colorimetric and fluorometric cyanide-selective sensors based on an intramolecular C-H⋅⋅⋅O hydrogen bonded solid emitter.

Rational Design of an ICT-Based Chemodosimeter with Aggregation-Induced Emission for Colorimetric and Ratiometric Fluorescent Detection of Cyanide in a Wide pH Range.

An alkoxy-substituted 1,3-indanedione-based chemodosimeter 1 with an aggregation-induced emission (AIE) characteristic was rationally designed and synthesized for the ultrasensitive and selective sensing of cyanide in a wide pH range of 3.0-12.0. The nucleophilic addition of cyanide to the ß-conjugated carbon of the 1,3-indanedione group obstructs intramolecular charge transfer (ICT) and causes a significant change in the absorption and fluorescence spectra, enabling colorimetric and ratiometric fluorescent detection of cyanide in a 90% aqueous solution. The cyanide-sensing mechanism is supported by single-crystal X-ray diffraction analysis, time-dependent density functional theory (TD-DFT) calculations, and 1H NMR titration experiments. Sensor 1 exhibits strong yellow fluorescence in the solid state due to the AIE effect, and the paper probes containing 1 can be conveniently used to sense cyanide by the naked eye. Furthermore, chemodosimeter 1 was successfully used for sensing cyanide in real environmental water samples.

Excited-state intramolecular proton transfer in the kinetic-control regime.

A new series of molecules bearing a 2,11-dihydro-1H-cyclopenta[de]indeno[1,2-b]quinoline (CPIQ) chromophore with the N-HN type of intramolecular hydrogen bond are strategically designed and synthesized, among which CPIQ-OH, CPIQ-NHAc and CPIQ-NHTs in solution exhibit a single emission band with an anomalously large Stokes shift, whereas CPIQ-NH2 and CPIQ-NHMe show apparent dual-emission property. This, in combination with time-resolved spectroscopy and the computational approach, leads us to conclude that CPIQ-OH, CPIQ-NHAc and CPIQ-NHTs undergo ultrafast, highly exergonic excited-state intramolecular proton transfer (ESIPT), while a finite rate of ESIPT is observed for CPIQ-NH2 and CPIQ-NHMe with a time constant of 117 ps and 39 ps, respectively, in acetonitrile at room-temperature. Further temperature-dependent studies deduce an appreciable ESIPT barrier for CPIQ-NH2 and CPIQ-NHMe. Different from most of the barrier associated ESIPT molecules that are commonly in the thermodynamic-control regime, i.e. found in the thermal pre-equilibrium between excited normal and proton-transfer tautomer states, CPIQ-NH2 and CPIQ-NHMe cases are in the kinetic-control regime where ESIPT is irreversible with a significant barrier. The barrier is able to be tuned by the electronic properties of the -R group in the NR-H proton donor site, resulting in ratiometric fluorescence for normal versus tautomer emission.

Sulfur-Based Intramolecular Hydrogen-Bond: Excited-State Hydrogen-Bond On/Off Switch with Dual Room-Temperature Phosphorescence.

We report O-H----S hydrogen-bond (H-bond) formation and its excited-state intramolecular H-bond on/off reaction unveiled by room-temperature phosphorescence (RTP). In this seminal work, this phenomenon is demonstrated with 7-hydroxy-2,2-dimethyl-2,3-dihydro-1 H-indene-1-thione (DM-7HIT), which possesses a strong polar (hydroxy)-dispersive (thione) type H-bond. Upon excitation, DM-7HIT exhibits anomalous dual RTP with maxima at 550 and 685 nm. This study found that the lowest lying excited state (S1) of DM-7HIT is a sulfur nonbonding (n) to π* transition, which undergoes O-H bond flipping from S1(nπ*) to the non-H-bonded S'1(nπ*) state, followed by intersystem crossing and internal conversion to populate the T'1(nπ*) state. Fast H-bond on/off switching then takes place between T'1(nπ*) and T1(nπ*), forming a pre-equilibrium that affords both the T'1(nπ*, 685 nm) and T1(nπ*, 550 nm) RTP. The generality of the sulfur H-bond on/off switching mechanism, dubbed a molecule wiper, was rigorously evaluated with a variety of other H-bonded thiones, and these results open a new chapter in the chemistry of hydrogen bonds.

Synthesis, X-ray Structure, Optical, and Electrochemical Properties of a White-Light-Emitting Molecule.

A new white-light-emitting molecule (1) was synthesized and characterized by NMR spectroscopy, high resolution mass spectrometry, and single-crystal X-ray diffraction. Compound 1 crystallizes in the orthorhombic space group Pnma, with a = 12.6814(6), b = 7.0824(4), c = 17.4628(9) Å, α = 90°, ß = 90°, γ = 90°. In the crystal, molecules are linked by weak intermolecular C-H···O hydrogen bonds, forming an infinite chain along [100], generating a C(10) motif. Compound 1 possesses an intramolecular six-membered-ring hydrogen bond, from which excited-state intramolecular proton transfer (ESIPT) takes place from the phenolic proton to the carbonyl oxygen, resulting in a tautomer that is in equilibrium with the normal species, exhibiting a dual emission that covers almost all of the visible spectrum and consequently generates white light. It exhibits one irreversible one-electron oxidation and two irreversible one-electron reductions in dichloromethane at modest potentials. Furthermore, the geometric structures, frontier molecular orbitals (MOs), and the potential energy curves (PECs) for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations. The results demonstrate that the forward and backward ESIPT may happen on a similar timescale, enabling the excited-state equilibrium to be established.

A ratiometric chemodosimeter for highly selective naked-eye and fluorogenic detection of cyanide.

A simple indole-based chemosensor (1) with a very low molecular weight of 207 g mol(-1) has been synthesized for the highly reactive and selective detection of CN(-) in aqueous media, even in the presence of other anions, such as F(-), Cl(-), Br(-), AcO(-), [Formula: see text] , SCN(-), [Formula: see text] , [Formula: see text] , [Formula: see text] , BzO(-), [Formula: see text] , and [Formula: see text] . The sensor achieves rapid detection of cyanide anion in 2 min, and the pseudo-first-order rate constant is estimated as 1.576 min(-1). The colorimetric and ratiometric fluorescent response of the sensor to CN(-) is attributable to the addition of CN(-) to the electron-deficient dicyanovinyl group of 1, which prevents intramolecular charge transfer. The sensing mechanism is supported by density functional theory and time-dependent density functional theory calculations. Moreover, sensor 1 exhibits both high accuracy in determining the concentration of CN(-) in real samples and 1-based test strips can conveniently detect CN(-) without any additional equipment. The detection limit of the sensor 1 (1.1 µM) for cyanide is lower than the maximum permissible level of CN(-) (1.9 µM) in drinking water.

Ratiometric fluorescent/colorimetric cyanide-selective sensor based on excited-state intramolecular charge transfer-excited-state intramolecular proton transfer switching.

A novel salicylideneaniline-based fluorescent sensor, SB1, with a unique excited-state intramolecular charge transfer-excited-state intramolecular proton transfer (ESICT-ESIPT) coupled system was synthesized and demonstrated to fluorescently sense CN(-) with specific selectivity and high sensitivity in aqueous media based on ESICT-ESIPT switching. A large blue shift (96 nm) was also observed in the absorption spectra in response to CN(-). The bleaching of the color could be clearly observed by the naked eye. Moreover, SB1-based test strips were easily fabricated and low-cost, and could be used in practical and efficient CN(-) test kits. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations further support the cyanide-induced ESICT-ESIPT switching mechanism. The results provide the proof of concept that the colorimetric and ratiometric fluorescent cyanide-selective chemodosimeter can be created based on an ESICT-ESIPT coupled system.