Two sets of new mononuclear
cyclometalated complexes of the types
[MIII(ppy)2(L)] (Ir1 and Rh1) and [MIII(bzq)2(L)] (Ir2 and Rh2) [where M = Rh/Ir; L = N-(furan-2-ylmethyl)-2-pyridinecarboxamide; ppy = 2-phenylpyridine
(1); bzq = benzo[h]quinoline (2)] are presented to understand the significant differences
of emission behaviors between Ir(III) and Rh(III) complexes. The complexes
were fully characterized by using physicochemical and spectroscopic
tools along with the detailed structural studies of Ir1 and Rh2 by single-crystal X-ray diffraction. Structural
analyses showed that in both complexes the metal exhibits a distorted
octahedral geometry. The geometries, electronic structures, lowest-lying
singlet–singlet absorptions, vertical singlet–triplet
excitation, and triplet–singlet emission behaviors of all the
complexes (Ir1–2 and Rh1–2) were examined by means of DFT and TDDFT approaches. In order to
find out the considerable differences in experimentally observed emission
properties of Ir(III) (5d6) and Rh(III) (4d6) complexes, the radiative and nonradiative processes were calculated
and compared quantitatively and somewhat qualitatively. The results
indicate that the smallest S1–T1 splitting
energy (ΔE
S1-T1), large
transition dipole moment (μS1), and reverse order
of energy states between the triplet metal-to-ligand charge transfer
(3MLCT) and triplet metal-centered (3MC) states
were responsible for the higher radiative process of Ir(III) complexes
than those of Rh(III) complexes. Since the nonradiative decay process
plays an important role in the photodeactivation process, the potential
energy profile for the deactivation process from 3MLCT
via 3MC was explored. In addition to the relative energies
of 3MLCT and 3MC states, the position of minimum
energy 3MC/1GS crossing point (MECP) was also
computed.
A new rhodamine-based Schiff base (L) has been synthesized and characterized by physicochemical and spectroscopic tools. This organic molecule selectively reacts with Cu 2+ ions with a remarkably significant optical change, which supports the development of a chemosensor for Cu 2+ ions as low as nanomolar level in aqueous medium. On the basis of the experimental work, the 'turn-on' colorimetric/fluorimetric spectroscopic change is due to Cu 2+ ion-assisted hydrolysis followed by spirolactam ring opening of the probe (L) in 20 mM HEPES buffer [pH 7.4; water/acetonitrile (9:1 v/v)]. The competitive ions do not affect the selectivity and specificity of the probe (L) in the detection of Cu 2+ ions. The cell imaging study using fluorescence microscope showed that this non-cytotoxic probe is useful to detect the distribution of Cu 2+ ions in AGS cells lines.
A newly designed and structurally characterized non-cytotoxic benzimidazole containing quinazoline derivative (HL) acts as a ‘turn-on’ greenish-yellow fluorescent sensor selective for Zn2+ions at as low as 39.91 nM in 5 mM HEPES buffer (DMSO/water: 1/5, v/v) at biological pH.
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