Over the last 25 years, the introduction of two dimensional (2D) materials has led to a revolution in condensed-matter physics. As opposed to the bulk semiconductor, the exciton binding energy in 2D systems can be as large as 0.5 eV, meaning that the exciton dominates the light-matter interactions. In this talk, excitons in heterostructures composed of transition metal dichalcogenide (TMD) 2D materials and molecular thin films are discussed. Time- and angle-resolved photoemission spectroscopy (tr-ARPES) is introduced as a tool for studying excitons in the perturbative regime, where exciton-exciton interactions are negligible. In addition to observing a new exciton species, the tr-ARPES shows that the band alignment in the WS2/MoSe2 heterostructure can be tuned from type 1 to type 2 by tuning the relative twist angle between the layers. Future experiments with organic thin film-TMD heterostructures are proposed. The talk is accessible to graduate students without a background in condensed-matter physics.