Premchendar Nandhikonda

Dual Fluorescent N-Aryl-2,3- naphthalimides: Applications in Ratiometric DNA Detection and White Organic Light-Emitting Devices

A ten element matrix of 5- and 6-substituted-(2,3)-naphthalimides was prepared for the appropriate placement of substituents necessary to promote dual fluorescence (DF). As prescribed by our balanced seesaw photophysical model this matrix yielded nine new DF dyes out of a possible ten compounds. From this set of nine DF dyes, 4-fluoronaphthalic amide (37) was selected as a probe for ratiometric detection of DNA and demonstration of panchromatic emission.

Highly Water-Soluble Monoboronic Acid Probes That Show Optical Sensitivity to Glucose Based on 4-Sulfo-1,8-naphthalic Anhydride

Two highly water-soluble monoboronic acid probes that display the more desirable off-on fluorescence response were synthesized based on 4-sulfo-1,8-naphthalic anhydride and a remarkable sensitivity for glucose rather than fructose and galactose was also observed.

An organic white light-emitting dye: very small molecular architecture displays panchromatic emission

The synthesis and photophysical characterization of a new white-light fluorophore is described. The optimization of excitation wavelengths allows the naphthalimide (NI) dyes to display blue, green or white light emission depending on the excitation wavelength.

An abiotic fluorescent probe for cardiac troponin I.

The first ratiometric fluorescent reporter was designed for the detection of cardiac troponin I (cTnI), a key protein elicited during cardiac muscle cell death. In designing this abiotic fluorescent probe, docking simulation studies were performed to predict the probe/protein interactions along the solvent exposed regions of cTnI. Simple cuvette titration experiments in aqueous buffered solution indicate remarkable selectivity for cardiac troponin in the clinically relevant nM region versus skeletal troponin.

A Comparative Study into Two Dual Fluorescent Mechanisms via Positional Isomers of N-hydroxyarene-1,8-naphthalimides

Three isomers of hydroxy substituted N-aryl-1, 8-naphthalimides based on N-aryl naphthalic anhydride fluorophore have been synthesized. The decrease in fluorescence intensity from ortho to para substitution of hydroxy group on N-aryl reveals that para substituted isomer undergoes ESEC (Excited State with Extended Conjugation) mechanism which is proved by low quantum yield and appearance of dual emission. The ortho isomer, however, has high quantum yield and no tautomer emission, indicating ESIPT (Excited State Intramolecular Proton Transfer) mechanism is not operating. Similarly, all these isomers show strong fluorescence quenching in presence of strong H-bonding solvents like DMSO and pyridine, but there was neither the shift of emission bands nor the appearance of new bands for proton transfer to these solvents. Thus, it also indicates the absence of excited state proton transfer mechanism. Both the ortho isomer, and to a greater degree the meta isomer, showed larger quenching constants (Kapp) with pyridine than DMSO. This trend opposes the hydrogen-bond affinity for these solvents with phenol and points to a 2-point recognition interaction. In addition, a naphthalimide derivative using 2-aminoimidazole was prepared and examined for optimal positioning of a six-membered ring hydrogen bond pattern. No dual fluorescence was observed for this compound either.

Theme and Variation on N -Aryl-1, 8-Napthalimides: Minimal Modification to Red-Shifted Fluorescence and Applications in Fluorescent Chemosensors

Our continuing efforts into the development of N-aryl-1,8-naphthalic dicarboximides (NI) as dual fluorescent (DF) dyes for biomedical applications has led to new insights into the photophysical features that these simple dyes can be designed to display. Consequently, the development of new DF dyes with improved fluorescent properties represents a major focus of our research. The first section of this review presents results involving a “minimal modification approach” to red-shifted absorption and fluorescence in NIs and affords some key design concepts for improved DF dyes. In this section, we demonstrate the significant effect of appropriately placed charges can have on the emission properties of these unique dyes. In the next section, dual fluorescent probes for the ions of potassium and sodium are introduced with the NI framework and crown ether receptors. The ratiometric features of these dyes from absorption as well as fluorescence spectroscopy are highlighted. Finally, in the third section, we demonstrate dual fluorescence detection of saccharides with the same DF dye component as our ion probe, in this case, however, a simple phenylboronic acid is utilized as a saccharide binding component.

New Dual Fluorescent Dyes Based on Modified “Excited State with Extended Conjunction” Photophysical Model

This review presents research that centers on verification of a new photophysical model for the excited state properties of N-phenyl-1,8-naphthalimides. The first section of the review highlights the critical advantages that two-color dyes possess relative to single color dyes with respect to internal calibration and quantitative analysis. Recent examples are provided to show the development of the modified photophysical model and the fluorescence properties on which this model is based upon. Results shown in this section serve as a guide or roadmap toward future strategies, specifically, which substituents are required for the promotion of dual fluorescence (DF). Based on these concepts, a 3×3 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of DF. The matrix elements included for this study were based on a predictive model that we propose as a seesaw balanced photophysical model. This model serves as guide to optimize the dual fluorescence emission from N-phenyl-1,8-naphthalimdes by appropriate placement of substituent groups at both the 4-position of the N-arene as well as the 4ʹ-position of the naphthalene ring. Steady-state fluorescence studies under a variety of solvents indicate that four of the nine dyes in the matrix are dual fluorescent. Given the difficulties in predicting excited state properties such as molecular fluorescence, this ratio of four out of nine “hits’ for discovering DF signifies proof of principle for this proposed model and should provide a rational basis for the synthesis of future DF 1,8-naphthalimide systems.

N-Aryl Arenedicarboximides as Tunable Panchromatic Dyes for Molecular Solar Cells

Three organic dyes designed as molecular dyads were prepared that feature a common naphthalimide acceptor and N-aryl donors. One of these incorporated an additional cyanoacrylic acid linker and conjugated thiophene bridge inserted between donor and acceptor groups. Electrochemical and photochemical characterizations have been carried out on nanocrystalline TiO2 dye-sensitized solar cells which were fabricated with these dyes as the sensitizing component. HOMO and LUMO energies were also calculated using TDDFT methods and validated by the cyclic voltammetry method. A key finding from this study indicates that computational methods can provide energy values in close agreement to experimental for the N-aryl-naphthalimide system. Relative to HOMO/LUMO energy levels of N719, the dyes based on naphthalimide chromophore are promising candidates for metal-free DSSCs.