In this study we examine charge transfer between graphene and molecular semiconductors, parahexaphenyl and C60. Through in situ measurements of the current, we directly probe the charge transfer as the interfacial dipole is formed. We demonstrate that adsorbed molecules do not affect electron scattering rates in graphene. However, the molecules introduce p-type doping with only about one thousandth of an electron transferred per molecule. In addition, we show results on charge trapping and light-assisted charge transfer within polar pentacene derivate dihydrotetraazaheptacene, supported by hexagonal boron nitride and graphene.