What Goes on in Photosystems at the Molecular/Atomic Level?
The energy transfer is achieved by a process called "resonance energy transfer". It needs the positioning of the donor and the acceptor in very close proximity to each other - the light harvesting complexes are optimized for this. This allows the collection of small amounts of light energy and still enables photosynthesis. The figure shows how this works schematically:



The figure is from this webpage, which gives a good introduction.