The effect of solvents on the absorption and emission spectra of 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP) laser dye has been studied in various solvents at 298 K. A bathochromic shift was observed in absorption and fluorescence spectra upon increase of solvent polarity, which indicates that this transition is π-π *. The ground and excited state dipole moments were calculated as 2.23 and 6.34 Debye, respectively. The dye solution in MeOH, n-heptane, and methyl isobutyl ketone gives laser emission in the blue region upon excitation by a 337.1 nm nitrogen pulse; the gain coefficient and emission cross section as well as normalized photostability have been determined. Excitation energy transfer from POPOP to rhodamine B and fluorescine was studied to improve the laser emission from these dyes. Such an energy transfer dye laser system (ETDL) obeys a long range columbic energy transfer mechanism with a critical transfer distance, R 0 , of 25 and 33Å and k q equal to 10.4 × 10 12 and 26.2 × 10 12 M −1 s −1 for the POPOP/RB and POPOP/fluorescine pair, respectively. The POPOP dye is highly photostable in polar protic and polar aprotic solvents, while it displays photodecomposition in chloromethane solvent via formation of a contact ion pair. The photochemical quantum yield and rate of photodecomposition depend on the electron affinity of solvent.

The titled dye (1) shows very high fluorescence quantum yield values as well as photostability. The dye undergoes molecular aggregation both in the ground state (at a critical concentration of ca. 2XKT4 mol dm-3) and in the excited state (giving excimerlike emission at ca. 600 nm). It displays solvatochromism in both emission and UV-visible absorption spectra. The dye does not give laser emission upon pumping ethanolic solutions with a nitrogen laser (XMC = 337.1 nm, peak power of 100 kW) but acts as an efficient quencher of l,4-bis(/S-pyridyl-2-vinyl)benzene (P2VB) laser dye. The quenching process obeys a static type mechanism. Equimolar mixtures of dye 1 and P2VB or 2,5-distyrylpyrazine (DSP) laser dyes also give no laser emission. With even higher peak power (200 kW, pulse duration of 8001 ps) a laser emission can be obtained from chloroform solutions of dye 1.

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