THE ELECTRONIC SPECTROSCOPY AND PHOTOPHYSICS OF SATURATED PHOSPHINES

The near-UV absorption spectra of PH3 and its trialkylderivatives trimethylphosphine (TMP), triethylphosphine (TEP), and tri-n-propylphosphine (TPP) are reported for the gas phase between 42 000 and 54 000 cm-1. The diffuse structure observed in the spectrum of PH3 is enhanced using second derivative (SD) spectroscopy, and the locations of 14 features are reported. The spacing between the lowest eight features (44 504 and 49 456 cm-1) is approximately constant, 707 ± 15 cm-1. The absorption spectra of the trialkylphosphines are completely diffuse, and are devoid of SD features. The absorption spectra shift to lower energies with increasing alkylation. Absorption maxima (and extinction coefficients) for TMP, TEP, and TPP are 49 850 (1.5 × 104), 48 080 (9.0 × 103), and 47 620 (6.0 × 103) cm-1 (M-1 cm-1). Unlike the saturated amines, which are strongly fluorescent in the gas phase, the trialkylphosphines do not produce measurable emission. An upper limit of 10-4 is placed on the emission quantum efficiency. TPP was found to quench the fluorescence of N,N-dimethyloctylamine with a rate constant of 8.5 × 108, M-1 s-1 in n-hexane solution at 283 K; this corresponds to ca. 0.042 times the diffusion-controlled value and 0.20 times the self-quenching rate constant of the amine. © 1992.