Radiative and radiationless transition phenomena in 1,4-, 1,3-, and 1,2-diazanaphthalene vapors

Abstract

A pulsed, frequency doubled dye laser has been used to study time and wavelength resolved emission from low pressure quinoxaline, quinazoline, and cinnoline vapors. The S₁, ¹(n−π*) states of quinoxaline and quinazoline undergo statistical limit intersystem crossing, while the S₂ (π−π*) states undergo S₂−S₁ and singlet‐triplet intermediate strong coupling. Excitation into S₂ yields a two‐component ``fluorescence'' having an S₁‐type emission spectrum, and a longer component lifetime 10²–10³ longer than predicted by the S₀−S₂ f number. This anomalous emission is discussed principally in terms of a sequential decay theory of Tric and co‐workers. Intermediate strong coupling appears to evolve into statistical limit coupling as a function of excitation energy. The ³B₂ quinoxaline collision free phophorescence lifetime is within a factor of 2 of its value in condensed phases at low temperature. Thus the existance of rotational degrees of freedom in the gas does not significantly enhance the T₁→S₀ intersystem crossing rate, in disagreement with a recent theory. Cinnoline exhibits no detectable long‐lived phosphorescence or intermediate strong coupling emission.