  We find a new class of exact solutions for rotating black holes in $f(R)$
gravity in presence of imperfect fluid. We find that the exact solutions are
holographically dual to a hidden conformal field theory. Moreover we consider
another class of exact solutions for rotating black holes in $f(R)$ gravity,
which is obtained through a Lorentz boost transformation on a static spherical
symmetry solutions in $f(R)$ gravity. We also find that the boosted exact
solutions are holographically dual to a hidden conformal field theory.
Comparing the CFT temperatures and the mode numbers of the two CFTs, we suggest
a conjecture that, "Two identical rotating black holes (the same mass and the
horizon) in $f(R)$ theory could be distinguished by looking at their dual CFT
temperatures, and the dual CFT mode numbers. The rotating black hole in the
presence of matter has higher CFT temperatures and higher CFT mode numbers,
compared to the vacuum boosted rotating black hole".
