2000 Volume 16 Issue 12 Pages 1323-1326
A specially designed experimental setup including a newly constructed KBr cell, a light source, a monochromator and an IR detection system suitable for strictly calibrated IR absorption measurements was constructed in order to elucidate strange phenomenon associated with cis-trans photo-isomerization at 6.26 µm of the azobenzene core located at the center of an aryl-ether dendrimer (L5AZO). The setup used an ordinary Nichrome source to measure the photon flux, irradiation area, and photon absorption rate as exactly as possible. The photon absorption rate was obtained as 1.2×10-3 photons/s·molecule and the absorption cross section of L5AZO molecules was estimated to be 3.1×10-19 cm2/molecule. Since these values of the absorption rate and absorption cross section are not abnormal, the occurrence of a simultaneous five-photon absorption is almost impossible. Therefore, the five-photon absorption and photo-isomerization shown by L5AZO suggested that the multiphoton process was not simultaneous absorption, but possibly a sequential absorption and energy storage until the equivalent energy of isomerization was reached.
