Conjugation Effects in the Generation of Dynamic Covalent Libraries of Bis-Imines from Substituted Aromatic Aldehyde and Amine Components.

The conjugation-driven stability and reactivity of bis-imine formation from the reaction of substituted aromatic aldehydes and amines bearing electron donor and acceptor groups were studied in two approaches involving aldehydes and amines with the substituents either conjugated (para position) or non-conjugated (meta position) to the reacting functional groups. The bis-imine from the reaction of a bis-amine (B) with different types of aldehydes (A) constituted an ABA module, whereas the reaction of bis-aldehydes with different amines resulted in a BAB module. The competitive reactions were also studied for a specified bis-amine (B1 or B2) in similar conditions with a mixture of different aldehydes, and the time-dependent generations of dynamic covalent libraries were followed.

Substituted thiourea incorporated rhodamine-based chemosensors for selective detection of aluminium ions.

Various metal ions' contemporary utility, biological essence and environmental impact have stimulated their selective and sensitive detection, particularly when present in traces. In this context, methodological explorations relying on structural and functional modulations of prime components and interactive parameters have been pivotal in developing chemosensors for selective detection of such metal ionic inputs. In this investigation, three thiourea-incorporated rhodamine B derivatives varying in their substituent modified covalent architectures were synthesized, and their photophysical signalling responses were monitored in the presence of different metal ions.

Anti-cancer potential of substituted "amino-alkyl-rhodamine" derivatives against MCF-7 human breast cancer cell line.

Breast cancer is the most prevalent diagnosed cancer among women and the main cause of morbidity and mortality. As for breast cancer, MCF-7 cells are an important candidate since they are widely utilized in research for estrogen receptor (ER)-positive breast cancer cell assays, and various sub-clones have been identified to reflect different classes of ER-positive tumors with varied levels of nuclear receptor expression. Rhodamines and its derivatives have shown a great interest over the past two decades due to their excellent structural and spectroscopic properties.

Chain length effect of spiro-ring -alkylation on photophysical signalling parameters in Fe(III) selective rhodamine probes.

Manifestation of photophysical signalling parameters in rhodamine derivatives exhibiting complexation induced spiro-ring opening is crucial for the realization of selective metal ion detection at trace levels. Substitution of various functional groups, such as alkylation to the core architecture, modulates the physico-chemical properties of such molecular probes. Despite a few studies, relationships between the extent of photophysical signal modulations and the chain lengths of -alkyl substituents are still elusive.

A Pyrene-Rhodamine FRET couple as a chemosensor for selective detection of picric acid.

Selective detection of nitroaromatic compounds such as Picric acid (PA), those being explosive materials and hazardous pollutants of environmental and biological concern is highly desirable. With the operational advantages of the chemosensing approach, a pyrene-rhodamine-B couple (1) was explored in this investigation as a ratiometric molecular probe for selective and sensitive detection of picric acid. The bi-fluorophoric probe displayed absorption and fluorescence enhancements along with colourless to reddish-brown colour transition as signaling responses in the selective presence of PA among all the nitro aromatic analyte investigated.

Selective DCP detection with xanthene derivatives by carbonyl phosphorylation.

Rhodamine derivatives (1-2) exhibited dual channel 'turn-on' photophysical signalling selectively with diethyl chlorophosphate (DCP) among various organophosphates (OPs), where the spiro-ring opening corresponds to the adduct formation through phosphorylation at their carbonyl O- nucleophilic centres.

Effect of n-alkyl substitution on Cu(ii)-selective chemosensing of rhodamine B derivatives.

Rhodamine B hydrazide-based molecular probes (1-10) were synthesized by derivatization with n-alkyl chains of different lengths at the hydrazide amino end. These probes exhibited selective absorption (A∼557) and fluorescence (I∼580) 'off-on' signal transduction along with a colourless → magenta colour transition in the presence of Cu(ii) ions among all the competitive metal ions investigated. The effective coordination of these probes to Cu(ii) ions under the investigated environment forming [Cu·L]2+ (L = 1-5) and [Cu·L2]2+ (L = 6-10) complexes led to their spiro-ring opening, which in turn was expressed through signatory spectral peaks of ring-opened rhodamine.

Two-step FRET mediated metal ion induced signalling responses in a probe appended with three fluorophores.

A tri-fluorophoric molecular probe (1) with three different derivatized fluorophores, i.e. anthracene (An), 7-nitrobenz-2-oxa-1,3-diazole (NBD) and rhodamine-B (Rh) appended on to a Tren [tris-(2-aminoethyl)amine] receptor was demonstrated to exhibit metal ion induced ratiometric fluorescence signalling through the initiation of a two-step fluorescence resonance energy transfer (FRET) process owing to a compatible and substantial spectral overlap of electronic absorption and fluorescence of initial donor-intermediate donor/acceptor-final acceptor pairs.

Good's buffer derived highly emissive carbon quantum dots: excellent biocompatible anticancer drug carrier.

Here, a facile one-step approach has been developed for the synthesis of carbon quantum dots (CQDs) from Good's buffer. The as-synthesized CQDs emit a bright greenish blue coloured fluorescence after exposure to a 365 nm UV-lamp illumination. The bright fluorescence nature of the CQDs has proven them to be excellent probes for cellular imaging.

Signaling preferences of substituted pyrrole coupled six-membered rhodamine spirocyclic probes for Hg(2+) ion detection.

Two six-membered spirocyclic rhodamine derivatives containing substituted pyrroles (1 and 2) were shown to exhibit preferential dual mode 'turn-on' signaling responses in the presence of Hg(2+) ions through complexation mediated spiro-ring opening. Although the rate of spiro-ring opening mediated through complexation is much slower in these probes in comparison to their five membered analogues, they exhibited a comparable sensitivity in metal ion detection.

Dual mode signaling responses of a rhodamine based probe and its immobilization onto a silica gel surface for specific mercury ion detection.

A 3-aminomethyl-(2-amino-1-pyridyl) coupled amino-ethyl-rhodamine-B based probe (2) exhibited simultaneous chromogenic and fluorogenic dual mode signaling responses in the presence of Hg(II) ions only among all the metal ions investigated in an organic aqueous medium. The spiro-cyclic rhodamine signaling subunit undergoes complexation induced structural transformation to result in absorption and fluorescence modulation. Its complexation induced signaling exhibited reversibility with various contrasting reagents having higher affinity towards Hg(II) ions, such as anions (AcO(-)) and competing chelating agents (En).

pKa Modulation in rhodamine based probes for colorimetric detection of picric acid.

Tuning the pKa in acid sensitive rhodamine spirolactam derivatives as a function of the solvent medium resulted in the selective detection of picric acid from its lower nitro phenolic analogues and a few other carboxylic acids.

Preferences of rhodamine coupled (aminoalkyl)-piperazine probes towards Hg(II) ion and their FRET mediated signaling.

The metal ion induced absorption and emission signaling pattern of rhodamine coupled bis-(aminopropyl)-piperazine (1-3) and (aminoethyl)-piperazine (4) based probes evaluated in MeCN as well as in an MeCN-H2O binary mixture medium revealed that these probes exhibit optical signaling perturbations to a varying extent in MeCN, however, their complexation induced signaling could be tuned selectively towards Hg(II) in the presence of an aqueous component in the solvent medium where competitive interactions such as metal-probe interactions and hydration of metal ions play the determining factor to induce aqueous promoted Hg(II) selectivity. Attachment of another fluorophore (anthracene and nitrobenzofurazan moieties in 2 and 3 respectively) at the other end of the rhodamine coupled bis-(aminopropyl)-piperazine receptor enabled these probes to facilitate a complexation induced fluorescence resonance energy transfer (FRET) from the excited fluorophore to the ring-opened rhodamine along with contributions through operative PET inhibition and rhodamine delactonization processes. The enhancement in absorption transition of these probes at ~557 nm upon selective Hg(II)-complexation and consequent colourless to pink colour change in the solution imply a chromogenic signaling pattern whereas simultaneous fluorescence amplification and/or FRET initiation lead to fluorogenic signaling to facilitate detection at lower concentration.

Alteration of selectivity in rhodamine based probes for Fe(III) and Hg(II) ion induced dual mode signalling responses.

The probes for metal ion induced chromo- and fluorogenic signalling responses alter their selectivity depending upon the nature of substituent as well as a function of solvent medium. 2 has shown selectivity towards Fe(III) ion, 4 towards Hg(II) ion while 3 is responsive towards both Fe(III) and Hg(II) ions.

Rhodamine-based probes for metal ion-induced chromo-/fluorogenic dual signaling and their selectivity towards Hg(II) ion.

The new signaling probes 2-6, rhodamine-B derivatives of various receptors which contain different donor atoms for effective metal ion coordination, were synthesized and their absorption as well as fluorescence spectral responses were evaluated in the presence of various metal ions. All these probes along with the reference probe 1 have exhibited optimal metal ion-induced absorption and fluorescence enhancement with Hg(II) ion in the longer wavelength region (>500 nm) in MeCN, exploiting the spectral characteristics of metal ion-induced structural transformation of rhodamine. The selectivity and sensitivity towards Hg(II) ion were better pronounced in MeCN-H(2)O (1 : 1 v/v) medium, implying the role of the solvent molecules, water in particular, in the preferential Hg(II) coordination environment.

Water induced chromogenic and fluorogenic signal modulation in a bi-fluorophore appended acyclic amino-receptor system.

An acyclic amino-receptor based bi-fluorophoric signaling system 3 exhibits water-induced simultaneous dual channel chromogenic and fluorogenic signal modulation. Its micromolar solution in various organic solvents exhibits an enhancement in absorption in the presence of water in trace amounts through the water-induced delactonization of rhodamine dye, rendering a visual perception as a function of colour change. The presence of water molecules also facilitates a fluorescence resonance energy transfer (FRET) from the excited nitro-benz-oxa-diazole fluorophore to rhodamine dye of 3 and leads to an enhancement of emission up to a second order of magnitude.

Transition-metal-induced fluorescence resonance energy transfer in a cryptand derivatized with two different fluorophores.

A laterally nonsymmetric aza cryptand has been derivatized with one 7-nitrobenz-2-oxa-1,3-diazole (fluorophore(1)) and one/two anthracenes (fluorophore(2)) to obtain 1 and 2. Their emission characteristics are probed in the presence of a number of transition metals and proton. In the case of 1, Cu(II), Zn(II), Cd(II), and proton afford a large enhancement of fluorescence, whereas Fe(II) and Ag(I) exhibit one order of magnitude less enhancement.

Perturbation of the PET process in fluorophore-spacer-receptor systems through structural modification: transition metal induced fluorescence enhancement and selectivity.

Several fluorescent signaling systems are built in the format fluorophore-spacer-receptor with ethylenediamine or N,N-dimethylethylenediamine as the receptor, anthracene as the fluorophore, and a methylene group as the spacer. The receptors are derivatized with different electron-withdrawing groups such as 4-nitrobenzene, 4-nitro-2-pyridine, and 2,4-dinitrobenzene, to perturb the photoinduced intramolecular electron transfer (PET) process from the nitrogen lone-pair to the fluorophore. The photophysical properties of these supramolecular systems and their fluorescence responses toward a number of quenching transition metal ions are reported.

Attachment of electron-withdrawing 2,4-dinitrobenzene groups to a cryptand-based receptor for Cu(II)/H+ specific exciplex and monomer emissions.

[reaction: see text] In a cryptand-based fluorescent signaling system with the configuration "fluorophore-spacer-receptor", attachment of the electron-withdrawing 2,4-dinitrobenzene groups to the cryptand receptor renders it highly selective for Cu(II). The system exhibits dual monomer and exciplex emissions in the presence of either of Cu(II) and H(+) as input with concomitant movements of one of the 2,4-dinitrobenzene groups.

Fluorescence enhancement of a signaling system in the simultaneous presence of transition and alkali metal ions: a potential AND logic gate.

Attachment of a laterally non-symmetric cryptand and a macrocycle at the 9- and 10-positions of anthracene leads to a fluorescent signaling system L1 which gives fluorescence enhancement in the simultaneous presence of alkali and transition metal ions.

Attachment of an electron-withdrawing fluorophore to a cryptand for modulation of fluorescence signaling.

The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[2-[(3-(oxomethyl)phenyl)oxy]ethyl]mine readily forms mononuclear inclusion complexes with both transition- and main-group-metal ions. The fluorophore 7-nitrobenz-2-oxa-1,3-diazole is attached to one of the secondary amines, to give an integrated fluorophore-receptor configuration. The fluorophoric system does not show any appreciable emission when excited due to an efficient photoinduced intramolecular electron transfer (PET) from the nitrogen lone pair.