The effect on 2D molecular crystallization caused by the addition of propylthioether side groups to the 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) molecule is investigated using scanning tunneling microscopy (STM). The molecule was deposited from 1-phenyloctane onto highly oriented pyrolytic graphite (HOPG) and imaged at the liquid-solid interface. We observe a different structure to previously reported arrangements of PTCDA due to the presence of the propylthioether side groups which inhibits the formation of the herringbone phase. A model, supported by calculations based oil density functional theory, is proposed ill Which molecules form rows stabilized by hydrogen bonding.