Terbium Crown-Ether Complex as a Stable Photoprobe

Terbium ion-4'carboxybenzo-18crown-6-ether complex (TbCCE) photoprobe is a sensitive and stable luminescent photoprobe used to detect low (9.4 x10(-9) mol L-1) concentrations of nalbuphine (NAL) in serum and pharmaceutical formulations. Here we discuss molecular modeling of the interacting species using DFT and TD-DFT. The results reveal strong binding energy of TbCCE (-153.36 kJ/mol) and explain the results of Stern-Volmer bimolecular quenching analysis due to the presence of NAL in the proximity (at 2.403 angstrom apart from Tb ion) of the emissive TbCCE. Ab Initio molecular dynamic (AIMD) simulations are used to explain the dynamical changes of TbCCE molecular kinetic energy in its S-1 state induced by collision with NAL. The AIMD simulates collisions between interacting molecules, which are reflected in the observed quenching of the photoprobe. Kinetic energy changes during molecular motions in the S-1 state of TbCCE in presence of NAL indicate energy transfer process leading to quenching starting at 57 fs at NAL-TbCCE distance is 1.6 angstrom. The excited state AIMD simulations carried out in this work suggest a new avenue for future research on luminescence quenching.