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Unravelling the Quenching Mechanisms of a Luminescent Ru II Probe for Cu II
Author(s) -
Santos André Ribeiro,
Escudero Daniel,
González Leticia,
Orellana Guillermo
Publication year - 2015
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201403340
Subject(s) - excited state , chemistry , density functional theory , photochemistry , quenching (fluorescence) , luminescence , intersystem crossing , photoluminescence , population , fluorescence , atomic physics , computational chemistry , materials science , physics , optoelectronics , demography , quantum mechanics , sociology , singlet state
Abstract We have investigated the photophysical and photochemical features of a luminescent heteroleptic Ru II ‐polypyridyl probe and of its corresponding Ru II ‐Cu II dinuclear complex formed upon the analyte binding through extensive density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations. The molecular probe contains the tailored imidazo[4,5‐ f ]‐1,10‐phenanthroline (IIP) ligand for simultaneously binding the Ru II core and the target metal ion in aqueous solution. We have rationalized the static photoluminescence quenching observed upon the Cu II coordination, on the grounds of distinct excited state deactivation mechanisms which are absent in the free Ru II complex probe. Additionally, the emission quenching found upon increasing the solution pH has also been investigated. When coordinated IIP deprotonates, the nature of the lowest excited state of its complex changes from 3 MLCT to 3 LLCT/ 3 IL. The strong base‐induced emission quenching can be understood in terms of both the energy‐gap law, since the 3 LLCT/ 3 IL states lie at a significantly lower energy than the 3 MLCT state increasing the contribution of non‐radiative mechanisms, and the expected slower radiative rates from such 3 LLCT/ 3 IL states. After Cu II binding, the lowest triplet excited state is similar to the analyte‐free probe in both energy and electronic nature. However, Cu‐centered non‐radiative excited states, populated after photoinduced electron transfer and intersystem crossing processes, are responsible for the population drainage of the emissive state.