The physical state of <i>para</i>-nitroaniline (<i>p</i>-NA) adsorbed in the channels of AIPO<sub>4</sub>-5 molecular sieves has been investigated by means of Raman spectroscopy. The Raman spectra show that the <i>p</i>-NA molecules within the channels form either a phase of head-to-tail chains similar to that in the solid crystaline <i>p</i>-NA with a characteristic ω<sub>3</sub> band at 1282 cm<sup>-1</sup> or a second phase, which is characterized by the similarly strong band around 1295 cm<sup>-1</sup>. This second phase consists of weakly interacting <i>p</i>-NA molecules in a similar pseudo-quinonoidic state as molten <i>p</i>-NA. Despite the missing formation of solid-like chains, molecules in the second phase are also highly orientated. However, their mean nutation angle with respect to the crystal axis z is about 16°, and, thus, it is larger than that of the chains.
W. Hill, F. Marlow, and J. Kornatowski, "Raman Spectroscopic Investigation of the Physical State of para-Nitroaniline in Channels of the AIPO4-5 Molecular Sieve," Appl. Spectrosc. 48, 224-227 (1994)