Synthesis, optical properties, laser activity and DFT studies of (E,E)-2,5-bis[2-(1-methyl-1H-pyrrole-2-yl)-vinyl]pyrazine (BMPVP)

The optical absorption and emission properties of (E,E)-2,5-bis[2-(1-methyl-1H-pyrrole-2-yl)-vinyl] pyrazine (BMPVP) have been studied in different solvents. The BMPVP dye shows strong solvatochromic emission upon changing the solvent polarity from nonpolar to polar; indicating that the emission state is of intramolecular charge transfer (ICT) character. The solvent effect on the spectral properties such as singlet absorption, molar absorptivity, oscillator strength and fluorescence quantum yield of BMPVP have been studied in detail. The Lippert-Mataga and Reichardt correlations were used to estimate the difference between the excited and ground state dipole moments (Δm). Electronic excited states in different solvents were investigated using TD-DFT. The intramolecular charge transfer was analyzed by the NBO technique. The BMPVP dye is highly photostable in polar protic and polar aprotic solvents, while it displays photodecomposition in chloromethane solvents via formation of a contact ion pair. The photochemical quantum yield depends on the electron affinity of the solvent. A solution of (8 × 10−5 M) BMPVP in THF, dioxane, CH3CN or DMSO gives laser emission when pumped by a nitrogen laser pulse (λex = 337.1 nm) of 800ps duration and 1.48 mJ pulse energy. The BMPVP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs) in ethanol with a fluorescence quenching rate constant of 1.40 × 109 M−1. The fluorescence data revealed that the dynamic quenching and the energy transfer play major roles in the fluorescence quenching mechanism.