Experimental and theoretical study of the intramolecular charge transfer on the derivatives 4-methoxy and 4-acetamide 1,8-naphthalimide N-substituted

Synthesis and photophysical properties of photostable 1,8-naphthalimide dyes incorporating benzotriazole-based UV absorbers

We developed a series of blue-emitting 1,8-naphthalimide dyes covalently attached to 2-(2-hydroxyphenyl)-2H-benzotriazoles that retard photodegradation of the fluorophore. The dyes displayed weaker fluorescence emissions than the parent 1.8-naphthalimide. Quantum chemical calculations suggested that the decreased fluorescence was caused by the nonradiative deactivation promoted through the excited state intramolecular proton transfer (ESIPT) in benzotriazole components. The dyes' phosphorescences in a degassed solution at 77 K were more efficient than that of the parent 1.8-naphthalimide, indicating a possible deactivation pathway through intersystem crossing. PMMA films doped with these dyes showed higher resistance against photoaging than the film doped with an equimolar mixture of constituent 1.8-naphthalimide and the benzotriazole derivatives. Thus, the covalently linked benzotriazole units slow fluorophore degradation not only by preferential absorption of harmful UV light, which is found in the film with a simple mixture of two components, but also by the nonradiative deactivation involved in benzotriazole units.

Highly photostable blue fluorescence dyes were developed by hybridization of 1,8-naphthalimides with benzotriazole-based UV absorbers enabling a non-radiative energy dissipation process of excited-state intramolecular proton transfer (ESIPT).

Experimental evidence of TICT state in 4-piperidinyl-1,8-naphthalimide – a kinetic and mechanistic study

The excited state processes in N-propyl-4-piperidinyl-1,8-naphthalimide have been studied by measuring its fluorescence spectra and decay curves in solvents of different polarity and viscosity and also in a frozen solvent glass.

Synthesis and Photophysical Studies on Naphthalimide Derived Fluorophores as Markers in Drug Delivery

Derivatives of 4-amino-1,8-naphthalimide containing a free alkyl chain bearing carboxyl group as linker and different substituents at 4-amino function have been synthesized, characterized and studied for their photophysical properties. Steady state fluorescence studies showed quantum yield varied from 0.45 to 0.65 with Stokes shift in the range of 5824-8558 cm(-1). Spectroscopic and physicochemical parameters, like electronic absorption, emission, and extinction coefficient were investigated in order to explore the analytical potential of compounds. Solvatochromic studies demonstrated that all compounds were sensitive towards the polarity of different solvents showing the highest degree of fluorescence in acetonitrile. In addition, the compounds in the presence of ions, viz. Na(+), K(+) and Mg(2+) at concentration of 0.1-2 equivalents, showed a decreasing trend in fluorescence with increasing ionic concentration. TCSPC set - up was used to measure the fluorescence lifetime of compounds, which was found to be bi-exponential with longer and shorter component at their respective amplitudes. The average lifetime of compounds was observed to be 5.76-9.96 ns indicating the possibility of their greater utilization in research and diagnosis.

Excited-state intramolecular hydrogen bonding of compounds based on 2-(2-hydroxyphenyl)-1,3-benzoxazole in solution: a TDDFT study

The excited-state properties of intramolecular hydrogen bonding in the compounds based on 2-(2-hydroxyphenyl)-1,3-benzoxazole (6 and its tautomers 6a and 6b) have been investigated using theoretical methods. According to the geometric optimization and IR spectra in the ground and excited states calculated by density functional theory (DFT) and time-dependent DFT (TD-DFT) methods respectively, the type of intramolecular hydrogen bonding N⋯HO in 6 and 6a is demonstrated to be significantly strengthened, while NH⋯O in the tautomers 6a and 6b are proved to be sharply weakened upon excitation to excited state S1. The calculated absorption peaks of 6 are in good accordance with the experimental results. Moreover, other compounds based on 6 that R1 and R2 are both substituted as well as that only R1 is substituted are investigated to understand the effect of substituent on intramolecular hydrogen bonding. It is found that the hydrogen bond strength can be controlled by the inductive field effect of the substituent. In addition, the intramolecular charge transfers (ICT) of the S1 state for 6 and its tautomers 6a and 6b were theoretically investigated by analyses of molecular orbital.

Crystallographic structure and quantum chemical computations of 1-(3,4-dimethylphenyl)-3-phenyl-5-(4-methoxyphenyl)-2-pyrazoline

In this study the experimental crystallographic structure and the calculated optimized geometric parameters, vibrational wavenumbers, (1)H NMR and (13)C NMR chemical shift values, electronic absorption maximum wavelength values, HOMO-LUMO analysis, and molecular electrostatic potential (MEP) of 1-(3,4-dimethylphenyl)-3-phenyl-5-(4-methoxyphenyl)-2-pyrazoline (in abbreviated 1h), molecule, (C24H24N2O), by using density functional theory (DFT/B3LYP) method with 6-311++G(d,p) basis set in the ground state have been reported for the first time. Furthermore the IR and Raman spectra of title molecule were simulated by using calculated vibrational results. Geometric parameters (bond lengths and bond angles) vibrational wavenumbers and (13)C &(1)H NMR chemical shift values for the mentioned compound calculated at B3LYP/6-311++G(d,p) level are in good agreement with the experimental data.

Effects of the 3- and 4-methoxy and acetamide substituents and solvent environment on the electronic properties of N-substituted 1,8-naphthalimide derivatives

The photophysical properties of polar molecules in solution with an intramolecular charge-transfer effect in the excited state depend strongly on the polarity and proticity of the solvents. UV-visible spectra of 1,8-naphthalimide and some N-substituted derivatives in acetic acid, acetonitrile, dichloromethane, and p-dioxane were carried out. Several molecular cluster geometries formed with N-substituted 1,8-naphthalimide derivatives and a large set of random positioning of some solvent molecules in their environment were optimized by a semiempirical method. It provided a complete screening of possible solute-solvent configurations and resulted in a multiple minima hypersurface of the supramolecular systems. With such local minima energies, the main thermodynamic association functions were found. They also provided selected cluster geometries for calculations of vertical electronic transitions with a time-dependent density functional theory (TD-DFT), if the lowest energy structures were considered. Calculated vertical electronic transition energies at the TD-DFT level were compared with experimental data. The experimental absorption UV-visible spectra for the six compounds in the four solvents were performed in our laboratory. Moreover, X-ray photoelectron spectroscospy of the 1,8-naphthalimide was carried out in the ICP-CSIC laboratory. Thermodynamic function values show different association energies between each solvent and the molecules, in correlation with the possibility of hydrogen bond formation and the polarity and dielectric constant of the solvents. The 3- and 4-acetamide 1,8-naphthalimide derivatives have the highest conformer number and the most negative Gibbs free association energy values for a determined solvent. This indicates the importance of the entropic factors.