Search for $ {\chi }_{c1}\to {\pi }^{+}{\pi }^{-}{\eta }_{c}$ via $ \psi (3686)\to \gamma {\chi }_{c1}$

Utilizing $ (2712.4\pm 14.3)\times {10}^{6}\text{}\text{}\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, we search for the hadronic transition process $ {\chi }_{c1}\to {\pi }^{+}{\pi }^{-}{\eta }_{c}$ following the decay $ \psi (3686)\to \gamma {\chi }_{c1}$. No significant signal is observed, and an upper limit of $ \mathcal{B}({\chi }_{c1}\to {\pi }^{+}{\pi }^{-}{\eta }_{c})$ is determined to be $ 3.1\times {10}^{-4}$ at 90% confidence level, which is 1 order of magnitude more stringent than the previous measurement.