Organic semiconductors are promising materials for the fabrication of next-generation organic-based electronic devices. In particular, PTCDA molecules are interesting for thin film development due to their rectangular shape and hydrogen bonding. Moreover, the electron properties of the organic thin film can be tuned by alkali metal doping. Here, we study the influence of Cs doping on the structural and electronic properties of the model system PTCDA/Aa(111). Using momentum microscopy and applying the framework of photoemission orbital tomography, we can simultaneously access changes in occupation of the molecular orbitals and determine modifications of the azimuthal orientation of the PTCDA molecules upon Cs doping. We can identify two structural Cs-PTCDA phases depending on the Cs concentration. With increasing Cs concentration, we observe a gradual structural reorientation of the molecules that is accompanied by a modification of the population of the molecular states. The structural reorientation of the pTCDA molecules can be attributed to the electrostatic interactions between the partially ionized Cs atoms and the negatively polarized oxygen end groups of PTCDA.