PABA is para-aminobenzoic acid. This is a "classical" push-pull substituted molecule. The amino group donates (pushes) and carboxyl group accepts (pulls). Compounds with push-pull substitution have low HOMO-LUMO gaps. PAPA was used as a UV-B absorbing sunscreen. Notice that the amino group is NOT sp²-hybridized but the N-atom is clearly pyramidal!
The MO eigenvalues of PABA are provided in the file behind the link eigenvalues. Find the eigenvalues of the HOMO and the LUMO and compare the HOMO-LUMO gap to the respective gaps in aniline and benzoic acid.