Spectroscopic investigation, photophysical parameters and DFT calculations of 4,4′-(1E,1′E)-2,2′-(pyrazine-2,5-diyl)bis(ethene-2,1-diyl)bis(N,N-dimethylaniline) (PENDA) in different solvents

Abstract

A comprehensive investigation on the photophysics of a π-conjugated potential push–pull chromophore system 4,4′-(1E,1′E)-2,2′-(Pyrazine-2,5-diyl)bis(ethene-2,1-diyl)bis(N,N-dimethylaniline) (PENDA) has been carried out spectroscopically. The optical absorption and emission properties of this molecule have been studied in different solvents. The molecule PENDA shows strong solvatochromic emission upon changing the solvent polarity from nonpolar to polar; indicating that emission state is of intramolecular charge transfer (ICT) character. The solvent effect on the spectral properties such as singlet absorption, molar absorptivity, oscillator strength, dipole moment and fluorescence quantum yield of PENDA have been studied in detail. Lippert–Mataga and Reichardt correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). Ground and electronic excited states geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TDDFT), respectively, with the Gaussian 09 package. A solution of (8×10−5M) PENDA in THF, dioxane, CH3CN and CHCl3 gives laser emission when pumped by a nitrogen laser pulse (λex=337.1nm) of 800ps duration and 1.48mJ pulse energy. PENDA dye displays fluorescence quenching by colloidal silver nanoparticles (Ag NPs) in ethanol. The fluorescence data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching mechanism.