The physical state of para-nitroaniline (p-NA) adsorbed in the channels of AIPO4-5 molecular sieves has been investigated by means of Raman spectroscopy. The Raman spectra show that the p-NA molecules within the channels form either a phase of head-to-tail chains similar to that in the solid crystaline p-NA with a characteristic ω3 band at 1282 cm-1 or a second phase, which is characterized by the similarly strong band around 1295 cm-1. This second phase consists of weakly interacting p-NA molecules in a similar pseudo-quinonoidic state as molten p-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)