Is infrared photosynthesis possible?
I would hardly ever say never where biology is concerned.  In this case that utilizing red rather than blue light for a plant would require many of the basic assumptions of photosynthesis in terrestrial plants to be revised, but since we're talking about another planet, that might not really be an issue.  

If we are asking only about how we could change our plants to work with IR light, I'd say that might take a few hundred million years of selection and its harder to imagine. 

Firstly photosynthesis in another planet doesn't have to fix carbon or produce oxygen - both of these chemical processes utilize the relatively greater energy produced in blue and red light photosynthesis we see in plants here. 

Secondly using IR would have its particular questions associated with it.  In this case the energy quanta are very small and in fact in the same range as chemical bond vibrational energies.  Such energy might be hard to capture with any efficiency since simple heat would tend to compete with the photon, so this would work better if the entire system were at a relatively low temperature.  

The leaves could be black or they could be completely clear by the way.