Abstract
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 Å 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 S1 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 S1 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 Å. The excited state AIMD simulations carried out in this work suggest a new avenue for future research on luminescence quenching.
The energy transfer process (ET) from the HOMO of the ligand to the LUMO localized on Tb3+ ion followed by emission from 5D4 level to different 7FJ of Tb3+ (experimental spectrum shows the transitions to J = 6, 5 and 4 levels).
