in Genesis 1:3 god creates light. There is light present, just not an obvious source from which it orignates.
Genesis 1:11-12 god creates vegetation, notice that he did this after he created light.
in Genesis 1:14-15 god creates stars as first source of light
In Genesis 1:16-18 he put a clear break between day and night by creating two big lights.
but this doesn't answer your question right? Everyone can throw with bible verses.
here's it in clear english.
First god the earth, oceans, etc.. then he created light, without clear origin(probaly god himself) then he created plants. the plants had water to drink from, earth to grow in, air to breathe, etc... the plants also had the light to live from.
After that god created the first big light sources(the stars), after he created the stars he created the sun and the moon. He used the sun and the moon to make a clear difference between day and night.
So you see, there was already light to give plants the needed energy for photosynthesis.
if you wish more explanation please say so.
Mike