Spectroscopy of amplified spontaneous emission laser spikes in phenyloxazoles. Prototype classes

Ultraviolet amplified spontaneous emission (ASE) laser spikes are demonstrated for the phenyloxazoles. The principal laser spikes are at 333 nm for 2-phenylbenzoxazole (PBO) and at 374 nm for 2,5-diphenyloxazole (PPO), with two laser spikes at 365 and 385 nm for 2-(1-naphthyl)-5-phenyl-1,3,4-oxadiazole (alpha-NPD), all in hydrocarbon solution at 298 K. The extended symmetrical molecule 1,4-bis(4-methyl-5-phenyloxazol-2-yl)benzene (DPOPOP) has a laser spike at 420 nm, The lasing action is stable with time for stirred hydrocarbon solutions deoxygenated by Ar bubbling. Gain coefficients up to 10 cm(-1) have been observed in the cases cited. It is demonstrated that the phenyloxazoles can be categorized by the ASE laser spike spectroscopy observed. In the simple case, ASE spike appears at the position of the strongest fluorescence vibronic peak. Phenyloxazoles with asymmetric substitution (PPO, alpha-NPD) exhibit dual laser spikes, with dominance of that laser spike corresponding to a vibronic band of secondary intensity, This highly anomalous behavior is attributed to two normal mode segments of the electronic systems, with solitonic transfer of vibrational distortion between the segments driven by entropic and energetic preference, It is demonstrated that ASE laser spectroscopy offers excitation dynamics information not revealed in stationary state spectroscopy.