How to politely turn down others' request for collaboration?

Question

When I first started my PhD, I would grab every opportunity to collaborate with others because there weren't many and I wanted to learn as much as possible. However, as I become a senior PhD student, more and more people invited me to collaborate with them which can be quite overwhelming sometimes and I found it hard to turn down these requests. I wonder if there is any way to politely turn down these requests, especially ones from researchers senior to me?

Answer 1

Thank you so much for keeping me in mind for this. Even though the idea sounds exciting, I'm currently swamped with work, and cannot join a new collaboration at this point. I'm very sorry!

Depending on whether you see the chance to collaborate in the future, or you just want to get rid of them: You can also add that they can contact you again at some later point, or even that you will contact them.