Fluorescence and NMR binding studies of N-aryl-N'-(9-methylanthryl)diaza-18-crown-6 derivatives

Thermodynamically feasible photoelectron transfer from bioactive π-expanded imidazole luminophores to ZnO nanocrystals

The chemical affinity between the nitrogen atom of the imidazole and the zinc ion on the surface of the nano oxide may be a reason for strong interaction of the ligand on nanoparticles causing the enhancement.

Sensitive and selective PET-based π-expanded phenanthrimidazole luminophore for Zn2+ ion

The novel photoinduced electron transfer (PET) chemosensor, 1-(1-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [MPPN] and its zinc complex were synthesised and characterized by electronic spectral and Frontier molecular orbital energy analysis. MPPN becomes efficient fluorescent chemosensor upon binding with metal ions and shows a strong preference toward Zn(2+) ion. Density Functional theory (DFT) calculations reveal that luminescence of free MPPN originates from its orbital structure in which two π-orbitals (HOMO and HOMO-1) of the imidazole ring are situated between two π-orbitals (HOMO-2 and LUMO) of the naphthyl fragment. Therefore the absorption and emission processes occur between the two π- orbitals (HOMO-2 and LUMO). The two higher energy imidazole orbitals (HOMO and HOMO-1) serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding with Zn(2+) ion, MPPN becomes a highly luminescent with λemi - 421 nm. The significant enhancement of luminescence upon binding with Zn(2+) ion is attributed to the stabilization of HOMO-2 and HOMO-1 π-orbitals of imidazole ring upon their engagement in new bonds with Zn(2+) ion. The affinity of MPPN to zinc ion is found to be very high [K = 6 × 10(6) M(-1)] when compared with other metals ions. The nonlinear absorption coefficient γ for MPPN is 1.9 × 10(-12) m/W and 3.9 × 10(-11) m/W for MPPN-Zn complex.

A new dual functional sensor: highly selective colorimetric chemosensor for Fe3+ and fluorescent sensor for Mg2+

A new artificial receptor 1 was synthesized for the detection of Fe(3+) and Mg(2+) in solution as a colorimetric and fluorescent sensor, respectively. The sensor exhibited highly selective and sensitive recognition towards Fe(3+) in CH(3)CN via color change from colorless to brown. Also it showed a significant fluorescence enhancement (70-fold) towards Mg(2+) in the mixture of solution CH(3)CN/H(2)O (8:2, v/v). The selectivity of either Fe(3+) or Mg(2+) was not interfered by the presence of other metal ions such as Cr(3+), Mn(2+), Co(3+), Ni(2+), Cu(2+), Ag(+), Cd(2+), Pb(2+), Ca(2+) and K(+) ions.

New fluorescent perylene bisimide indicators--a platform for broadband pH optodes

Asymmetric perylene bisimide (PBI) dyes are prepared and are shown to be suitable for the preparation of fluorescence chemosensors for pH. They carry one amino-functional substituent which introduces pH sensitivity via photoinduced electron transfer (PET) while the other one increases solubility. The luminescence quantum yields for the new indicators exceed 75% in the protonated form. The new indicators are non-covalently entrapped in polyurethane hydrogel D4 and poly(hydroxyalkylmethacrylates). Several PET functions including aliphatic and aromatic amino groups were successfully used to tune the dynamic range of the sensor. Because of their virtually identical spectral properties, various PBIs with selected PET functions can easily be integrated into a single sensor with enlarged dynamic range (over 4 pH units). PBIs with two different substitution patterns in the bay position are investigated and possess variable spectral properties. Compared with their tetrachloro analogues, tetra-tert-butyl-substituted PBIs yield more long-wave excitable sensors which feature excellent photostability. Cross-sensitivity to ionic strength was found to be negligible. The practical applicability of the sensors may be compromised by the long response times (especially in case of tetra-tert-butyl-substituted PBIs).