A dark, excited electronic state of thiophosgene in the near ultraviolet

Authors:

• Andrzej Maciejewski,
• M. Szymanski,
• R.P. Steer

Abstract

The absorption, emission and excitation spectra of thiophosgene, Cl₂CS, have been measured in inert perfluoroalkane solvents. A new, weak (f≈5 ×10^-5 band at 285 ≤λ≤340 nm has been positively identified in the absorption spectrum of the pure, monomeric solute. Excitation in this band populates a "dark" excited state (DES) which exhibits no measurable emission (φ_f≤10^-8) at any wavelength between 330 and 800 nm. The lifetime of the DES is estimated on this basis to be substantially less than a picosecond as a result of its rapid radiationless decay to the ground state. The preferred identify of this state is one of primarily ¹(n^O_S, π^*2_CS doubly excited configuration, although a triplet of ³(n_Cl, π^*_CS) configuration cannot be ruled out altogether. The DES absorption is overlapped to the blue the strong ¹A₁-¹Ain1 transition which populates the fluorescent ¹(π, π^*) state. Deconvolution of the two absorption bands, and measurement of the lifetime and corrected quantum yields of emission gives values of the radiative and total non-radiative rate constants of the fluorescent state of 1.0×10⁷ and 2.3×10⁸s^-1, respectively. © 1992.