Molecular molybdenum sulfides, or thiomolybdates, are well-established noble-metal free molecular catalysts for the hydrogen evolution reaction (HER). To-date, there is a knowledge-gap regarding the impact of organo-functionalization on reactivity, stability and heterogenization of this compound class. Here, we report the development of synthetic routes for controlled introduction of organic N-donor ligands as a first step toward establishing structure-property-reactivity relationships in this new compound class. Photophysical studies combined with computational modelling are used to rationalize trends in the observed light-driven homogeneous HER activity. This work lays the foundation to develop organo-functionalized thiomolybdate HER catalysts suitable for covalent or supramolecular linkage to photosensitizers and for anchoring on heterogeneous supports, e.g. photocathodes.