Interest in artificial solid-state molecular rotator systems is growing as they enable systems to be designed for achieving specific physical functions. The phase transition behavior of four halomesitylene crystals indicated dynamic in-plane molecular rotator characteristics in dibromoio-domesitylene, tribromomesitylene, and dibromomesitylene crystals. Such molecular rotation in diiodomesitylene crystals was suppressed by effective I center dot center dot center dot I intermolecular interactions. The in-plane molecular rotation accompanied by a change in dipole moment resulted in dielectric phase transitions in polar dibromoiodomesitylene and dibromomesitylene crystals. No dielectric anomaly was observed for the in-plane molecular rotation of tribromomesitylene in the absence of this dipole moment change. Typical antiferroelectric-paraelectric phase transitions were observed in the dibromomesitylene crystal, whereas the dielectric anomaly of dibromoiodomesitylene crystals was associated with the collective in-plane molecular rotation of polar pi-molecules in the pi-stack. We found that the single-rope-like collective in-plane molecular rotator was dominated by intermolecular I center dot center dot center dot I interactions along the pi-stacking column of polar dibromoiodomesitylene.