Abstract

We report here for the first time the observation of both fluorescence and phosphorescence emissions from extensively purified samples of pyridine. An ultra-pure sample of pyridine was obtained through the following purification steps. E. Merck spectrograde pyridine was first treated with hydrochloric acid (GR arade) and the pyridine hydrochloride thus formed was subjected to repeated fractional distillation. The final middle fraction pyridine hydrochloride was then treated with sodium hydroxide. The pyridine liberated was fractionally distilled several times, dried over anhydrous sodium hydroxide, and finally fractionated before use. Pyridine when freed of impurities (viz., pyrazine) has been found to exhibit weak but readily observable fluorescence as well as phosphorescence emissions, both of π, π * character, in its pure crystalline state and in a variety of glassy and crystalline matrices (e.g., benzene, cyclohexane, methylcyclohexane, ethanol and water) at 77 K. Phosphorescence of pyridine is characterized by a long phosphorescence lifetime (τ~ 2s) and a broad and structureless spectrum with λ_max~ 420 nm. The fluorescence spectrum (λ_max~ 290 nm) shows some vibrational structure in crystalline media. In addition to these S₂ ( π, π^*) → S₀ and T₁ ( π, π^*) → S₀ emissions, a very weak emission attributable to S₁ ( n, π^*) → S₀ fluorescence (stretching a spectral region 310 — 350 nm) has also been observed in the emission spectrum of pyridine in rigid matrices. No fluorescence emission could be dected either in the vapor or in solution phase at room temperature.

© 1984 Optical Society of America