Ok...so your talking about:
1-(4-phenylphenyl)propan-2-amine and 1-(4-benzylphenyl)propan-2-amine. I have not heard of any bioassays on this material and a quick search revealed nothing of interest.
1-[4-(3-phenylpropyl)phenyl]propan-2-amine was found to be a 5-HT2A agonist (60nm) approximately twice as potent as its methoxy parent:
1-[4-(3-Phenylalkyl)phenyl]-2-aminopropanes as 5-HT2A Partial Agonists
Cynthia S. Dowd,,, Katharine Herrick-Davis,, Christina Egan,, Ann DuPre,, Carol Smith,, Milt Teitler, and, Richard A. Glennon,
Journal of Medicinal Chemistry 2000 43 (16), 3074-3084
Are you thinking the tert-butyl group would mimic 4-phenylethyl/4-phenylmethyl?