UV–visible absorption, fluorescence characteristics and laser activity of (E,E)-2,5-bis(4-methoxystyryl)pyrazine (BMSP)

The electronic absorption and emission spectra of (E,E)-2,5-bis(4-methoxystyryl)pyrazine (BMSP) dye was studied in various solvents at 298 K. A bathochromic shift was observed in absorption spectrum(ca. 10 nm) and fluorescence (ca. 20 nm) spectra upon increase of solvent polarity, which indicates that the transition is π−π⁎ in nature and the singlet excited state of BMSP is more polar than the singlet ground state. The fluorescence quantum yield of BMSP increases as the solvent polarity increases due to solvent of polarity decreasing the vibronic mixing between 1(π, π⁎) and 1(n, π⁎) states of BMSP. BMSP dye is insoluble in water but undergoes solubilization in the hydrocarbon core of micelles such as SDS( anionic surfactant), CTAB(cationic surfactant) and TX-100 (neutral surfactant). Ground and excited state protonation constants of BMSP were calculated as -0.2 and 5.26 respectively which indicates that the excited state of BMSP is more basic than the ground state. The photochemical quantum yield (φc) of photo-oxidation of BMSP was calculated in DMSO, EtOH and CHCl3. The values of φc were found to be 0.004, 0.0052 and 0.009 in DMSO, EtOH and CHCl3, respectively. Dye solutions in DMSO, EtOH and CHCl3 give laser emission in the blue region excitation by a 337.1 nm nitrogen pulse. The gain coefficient(α), emission cross section(σe) and fluorescence lifetime have been determined. Excitation energy transfer from BMSP to rhodamine B was studied to improve the laser emission from this dye when excited by 337 nm.