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The impact of the substitutional position of the chorine atom on the non-linear optical (NLO) response of chalcone derivatives is reported in this paper. Two thienyl-chalcone derivatives, (

Anion to nerve agent simulant detection by relay recognition has been designed and realized for the first time with sequence specificity (F− → DCNP) via a fluorescence “off–on–on” mechanism. The discrimination of DCNP and DCP via a CIFE (cyclization induced fluorescence enhancement) mechanism has also been demonstrated here. Test strips based on the sensors with F− and DCNP are fabricated, which can act as convenient and efficient nerve agent and F− test kits. The origin of the sequence specificity of different fluorescence recognition was revealed through single X-ray crystal and NMR analysis.

A benzothiazole conjugated quinoline derivative appended with rhodamine-6G acts as an efficient FRET-based single molecular switch for Fe3+. The structure of the probe was confirmed through its single crystal X-ray study. The sensor demonstrates an immediate fluorescence ratiometric response specific towards Fe3+ which also allows facile naked-eye detection of Fe3+. The probe is highly selective only towards Fe3+ in comparison to other environmentally important cations, including Fe2+. Moreover, the detection limit was found to be in the 10−8 M range for the recognition of Fe3+.

A new probe 2-benzo[1,2,5]thiadiazol-4-yl-isoindole-1,3-dione (BTI) based on the Gabriel reaction mechanism was synthesized and characterized for the specific detection of hydrazine with high selectivity against other amines in an organo-aqueous solution. Upon hydrazinolysis of BTI in the presence of hydrazine in a H2O–DMSO (4 : 6, v/v) solution (10 mM HEPES buffer, pH 7.4) at room temperature, the chemosensor produces fluorescent aminobenzthiadiazole with a maximum emission at 498 nm along with a color change from colorless to green, allowing selective colorimetric and fluorometric detection of hydrazine by the naked eye. Probe BTI was also successfully applied in vapor phase hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BTI coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The experimental detection limit of hydrazine is 2.9 ppb, which is well below the accepted limit (10 ppb) for hydrazine set by the U.S. Environmental Protection Agency (EPA). DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of probe and hydrazinolysis products. Additionally, probe BTI could also be applied for the imaging of hydrazine in living cells.

Three carbazole based benzimidazole derivatives exhibiting the effect of intramolecular charge transfer (ICT) caused by the donor–acceptor interaction between their carbazole and benzimidazole units were synthesized. Their photophysical properties were systematically investigated in various solvents with different polarities. Positive solvatofluorochromic effects were observed with the change of solvent from non-polar to polar for all of the three dyes. The synthesized compounds presented proton-induced absorption as well as ratiometric emission changes, indicating that these compounds might be used as proton sensors. The dyes in their solid state are also able to detect acid vapours. The optimized structures of the dyes and their protonated forms were calculated by density functional theory calculations.

For ratiometric, fluorogenic and “naked eye” detection of the environmentally and biologically important ions Hg2+ and OCl− in one platform, a 2-(2′-hydroxyphenyl)-benzothiazole (HBT) inserted thiolactam containing a new rhodol system, spirothiolactamized benzothiazole substituted N,N-diethylrhodol (STBR), is designed and synthesized. We can detect Hg2+ and OCl− in solutions by a simple, easy-to-synthesize practical ratiometric chemodosimeter with two different modes of reactions with a low detection limit. The observed color in the presence of Hg2+ or OCl− may arise from the reaction of Hg2+ or OCl− with STBR – the thiolactam moiety is broken and it helps to achieve maximum π–π* conjugation which results in a brilliant red fluorescence. From 1H-NMR and ESI-MS data, it is clear that the modes of the reaction for Hg2+ and OCl− are different. Test strips are also prepared to observe color changes. The sensing phenomena are fruitfully applied for live-cell imaging in Saccharomyces cerevisiae cells (from a short to long time range, 0 min to 120 min). The single crystal X-ray structure of the synthesised ESIPT rhodol moiety is also reported.

Based on excited state intramolecular proton transfer (ESIPT) and chelation enhanced fluorescence (CHEF) mechanisms, a new fluorescence ratiometric probe for Al3+ was designed and synthesized, and its structure was confirmed through single crystal X-ray study. This probe is capable of showing excited state intramolecular proton transfer through two different pathways. The introduction of Al3+ in a mixed aqueous solution with the probe results in an abrupt change in the photophysical properties of the probe. A ratiometric emission profile was observed in the presence of Al3+. Interestingly, the presence of other metal ions (especially trivalent ions, e.g. Fe3+, Cr3+, Ga3+ and In3+) do not perturb the fluorescence intensity of the probe (except Cu2+ and Pb2+, where slight changes were noticed). This indicates that the probe shows high affinity towards Al3+. The ratiometric sensing phenomenon may be explained by the presence of two different mechanisms, namely, excited state intramolecular proton transfer and chelation induced enhanced fluorescence, which are demonstrated by the probe in presence of Al3+ in the excited state. The complexation of the probe with Al3+ inhibits excited state intramolecular proton transfer while the chelation induced enhanced fluorescence mechanism becomes dominant. The probe efficiently detected the cellular uptake of Al3+, which is demonstrated here with human blood-cell imaging. Moreover, the detection limit was found to be 6.72 × 10−8 M.

The “Addition–NGP (neighbouring group participation)–Elimination” technique has been used for the ratiometric sensing of H2S/HS−. We report herein the sensing of H2S by the nucleophilic addition of H2S/HS− to a –CHO group of R1 adjacent to naphthyl hydroxyl followed by NGP of thiol through a probable six-membered transition state that undergoes the cleavage of the dinitrophenyl ether moiety. In contrast, R2 undergoes a probable addition and elimination mechanism forming a Meisenheimer complex, which also cleaves the ether moiety. However, herein, the reaction is very slow compared to R1, which works through NGP. The probe can be highly promising for selectivity and sensitivity, to detect H2S/HS− with rapid response (

The monohydrazone of quinoxaline aldehyde (HOQA) is found to be a ratiometric and colorimetric probe for Ni2+. HOQA shows a remarkable color change from colorless to yellow upon specific and selective binding to nickel that can be identified even by the naked eye. The cation recognition property of the receptor is monitored by UV-vis and 1H-NMR titrations and also by DFT (Density Functional Theory) and TD-DFT (Time Dependent Density Functional Theory) calculations.

A rhodamine–quinoline based chemodosimeter (RHQ) has been designed, synthesized and characterized in this paper. The structure of the sensor is confirmed through single crystal X-ray study. It detects hypochlorite (OCl−) selectively among other analytes studied. It showed colorimetric and orange-red fluorescence “turn-on” upon addition of OCl−. The OCl−-promoted ring opening of the rhodamine spirolactam ring in RHQ evokes a large absorbance as well as fluorescence enhancement in water–acetonitrile (1/1, v/v) medium with no significant response to other competitive analytes. Furthermore, we demonstrate here that RHQ can endogenously detect OCl− in human blood cells (peripheral blood mononuclear cells). It also exhibits excellent performance in the “dip stick” method. The optimized structure of the probe is calculated by density functional theory calculations. Moreover, the limit of detection of the probe is in the 10−8 M range.

Our designed chemosensor, rhodamine-HBT-dyad (RHD), selectively detects two biologically important ions (Al3+ and Zn2+) at two different wavelengths (‘naked-eye’ colors red and green, respectively) through two different mechanisms (i.e. FRET and ESIPT) at ppm level. The sensor can also detect the Al3+ ion through displacement of the Zn2+ ion in vivo.

A new pyrene thiazole conjugate (PTC) amine fluoroionophore was synthesized and characterized. The single crystal XRD structure of PTC has been established. The fluoroionophore PTC showed selectivity toward Sn4+ by switch on ratiometric fluorescence among the 16 metal ions studied in HEPES buffer medium with a detection limit of 6.93 μM. The interaction of Sn4+ with PTC has been further supported by absorption studies, and the stoichiometry of the complex formed (2 : 1) has been established on the basis of fluorescence and ESI-MS. Competitive ion titrations carried out reveal that the Sn4+ can be detected even in the presence of other metal ions of bio-importance. Moreover, the utility of the fluoroionophore PTC in showing the tin recognition in live cells has also been demonstrated using Vero 76 cells as monitored by fluorescence imaging. The tin complex of PTC was isolated, and the structure and electronic properties of [PTC–Sn] has been established by DFT and TDDFT calculations. The isolated tin complex [PTC–Sn] has been used as a molecular tool for the recognition of anions on the basis of their binding affinities toward Sn4+. [PTC–Sn] was found to be sensitive and selective toward sulphide ions among the other 12 anions studied. The selectivity has been shown on the basis of the changes observed in the emission and absorption spectral studies through the removal of Sn4+ from [PTC–Sn] by S2−.

A quinoxaline based colorimetric nickel sensor, HQAP [2-(quinoxalin-2-ylmethyleneamine)phenol] with high selectivity and sensitivity toward Ni2+ ions is shown to have potential for practical use. The absorption maximum of HQAP shows a large ratiometric shift from 306 to 570 nm (ΔI = 264 nm) in the presence of Ni2+ ions, and the color changes from colorless to deep violet only upon addition of Ni2+ which is very easily observed by the naked eye (the detection limit of Ni2+ is as low as 4.16 μM in solution). The predicted binding mode (2 : 1) from spectral analysis and Job's plot was confirmed by the single crystal X-ray structure of the complex.

A new rhodamine based chemosensor, cyano-rhodamine, has been designed and synthesized with a green approach which shows a specific 'C-CN' bond breaking with the action of the Pd(2+) ion to produce the specific color and fluorescence of rhodamine 6G itself in solution and in HeLa cells.

A new fluorescent probe was synthesized from rhodamine-6G and 6-(hydroxymethyl) picolinohydrazide for the sensing of Fe(3+) in an aqueous environment. The structure of the sensor was confirmed through its single crystal X-ray study. It exhibits a high specificity and sensitivity towards Fe(3+) over other interfering heavy and transition metal ions (HTM). The turn-on greenish-yellow fluorescence and a colorimetric change from colourless to pink were observed upon addition of Fe(3+) which evokes almost 116- and 23-fold enhancement in absorbance and emission intensity respectively in an acetonitrile-water (1:1, v/v, 25 °C) solution at a neutral pH (pH = 7.2). The Fe(3+) promoted ring opening of the spirolactam framework to the open chain amide platform of the sensor is responsible for its visible colour change and turn-on fluorescence activity. It also exhibits an excellent performance in the "dip stick" method. Moreover the limit of detection of the probe is in the 10(-8) M range.

Photoreactions of isoquinoline-1,3,4-triones and oxazoles with different substituents were found to give different chemo-, regio- and diastereoselectivities. The substituent at the C5 on the oxazole ring showed great influence on the chemoselectivity of the photoreaction as well as on the transformation of the photocycloadducts. The 2-methyl-5-methoxyoxazoles reacted with isoquinoline-1,3,4-triones rapidly and gave spirooxetanes with high regio- and diastereo-selectivity. Diastereoselectivity in the reaction of 2-phenyl-5-methoxyoxazoles with isoquinoline-1,3,4-triones was relevant to the substituent on the 4-position on the oxazole ring. Replacement of the 5-methoxy group with 5-methyl or 5-phenyl resulted in significant decrease on the reactivity of the oxazole as well as change on the diastereoselectivity in photocycloaddition with isoquinoline-1,3,4-triones. Acid-mediated transformations of the photocycloadduct spirooxetanes was found to give different type of products including β-hydroxy-α-aminocarbonyl compounds and spiroisoquinolineoxazolines under different reaction conditions. Substituents on the spirooxetanes as well as the type and amount of acid used in the reaction played important roles in determining the type and diastereoselectivity of the products in the transformations.

A new fluorescence rhodamine derivative bearing an 8-aminoquinoline moiety has been designed and synthesized for selective sensing of Pd(2+) in the presence of other competing metal ions in aqueous media. Pd(2+) induced spirolactam ring opening of rhodamine is confirmed for the first time by the X-ray crystal structure of the bound Pd(2+)-complex.