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

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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.