Investigation of Excitation Wavelength and Solvent Polarity Dependence of Dual Fluorescence of A Newly Synthesized Schiff Base, N-(4-(Dimethylamino) Benzylidene)-2h-1, 2, 4-Triazol-3-Amine (Dmaba-Amtr)
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Date
2009-07
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Addis Ababa University
Abstract
Steady state absorption, fluorescence excitation and emission spectra of DMABA-Amtr have been
measured at room temperature in cyclohexane (CHEX), 1,4-dioxane (DOX), dichloromethane (DCM),
acetonitrile (ACN) and hexanol solutions. The compound is found to exhibit dual emission in polar
solvents while a single emission was observed in a nonpolar solvent cyclohexane. The effect of solvent
polarity on the absorption spectra shows a general bathochromic shift. Dependence of the emission
spectra on solvent polarity and excitation wavelength has also been studied. The fluorescence excitation
spectra of DMABA-Amtr monitored at different emission bands are found to be different. Moreover, area
normalized emission spectra in polar solvents exhibit an isoemissive point showing the presence of two
equilibrated ground state conformations of the same molecule. Thus, the presence of two different
conformations of the same molecule in the ground state in polar solvents has led to two wxcited states,
locally excited (LE) and charge transfer (CT), and thereby results in the dual fluorescence of the
compound.
The experimental studies were supported by computational results, force field theory/ Molecular
Mechanics/ MM+
, by making use of Hyperchem 7.5 software. The ground state geometry optimization
and value of the ground state dipole moment was computed at Density Functional Theory (DFT) level
with B3LYP functional and 6-31G basis set.
On the basis of the experimental and computational results, two conformers of DMABA-Amtr are
suggested which are stable in the ground state, equilibrated in polar solvents at room temperature that
give rise to dual fluorescence up on excitation.
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Keywords
Investigation, Excitation Wavelength, Solvent Polarity, Dual Fluorescence, Newly Synthesized, Schiff Base