Fluorescence Lifetime and Quenching Rates for N,N,N′,N′-Tetramethyl- P -Phenylenediamine in the Vapor Phase

The fluorescence lifetime of N,N,N′,N′-tetramethyl-p-phenyIenediamine (TMPD) in the vapor phase has been determined to be 3.2 ± 0.3 ns for excitation at 337 nm. The rate constants for quenching of electronically excited TMPD by ground-state TMPD, O₂, and CO₂ have been determined to be <1 × 10⁻¹⁰ cm³/s, (9.9 ± 1.0) × 10⁻¹⁰ cm³/s, and <4 × 10⁻¹³ cm³/s, respectively. The rate for TMPD implies that self-quenching is negligible up to pressures of at least 10 Torr. The quenching rate by oxygen is sufficiently high to ensure that use of TMPD as a quantitative marker for fuel evaporation in exciplex-based vapor/liquid visualization systems is probably not possible if significant quantities of oxygen—as would be the case in combustion environments—are present.