37 research outputs found
Cancellation of Contact Quenching : A Simple Concept for Selective Chemosensing of Basic Fluoride and Acetate Anions
A weakly fluorescent acid-base pair formed by reacting fluorescent acridine orange with the quencher picric acid is reported for the detection of basic fluoride and acetate anions. Deprotonation by these anions causes disengagement of the fluorescent acridine orange from the quencher, picric acid. This phenomenon cancels the quenching existing in the native probe, thereby allowing for the optical signalling of fluoride and acetate anions by color modulation as well fluorescence switch-on response. Anions such as Br-, I-, Cl-, NO3-, SCN-, HSO4-, and H2PO4- offer no detectable interferences even in excess concentrations
Synthesis of macrocycles derived from vanillin and isovanillin
5-10Readily available vanillin 1 and isovanillin
2 have been exploited for the first time to synthesise thia and aza-bridged
macrocycles. Utilising a common approach, 1 and 2 are first
converted into the corresponding key intermediates, dicholoro compounds 5
and 10. Cyclocondensations of these molecules with Na2S under
high di lution provide thia-bridged
macrocycles 6 and 11 and with
p-toluenesulphonamide under basic condition, the aza- bridged macrocycles
7 and 12, respectively are obtained. The structures are fully supported
by elemental analysis, mass and high resolution NMR data. Variable NMR
measurements on 6 and 11 suggest that these macrocycles are
conformationally mobile even at -55°C on the
NMR time scale
Attempt towards [2,2](2,4) anti-thiazolophane: Synthesis and conformational analysis of the key intermediate bislactone-bridged thiazolophane
127-131Using the
Mukaiyama's protocol, compound 11 is successfully assembled via
lactonization of hydroxy acid 9. On the basis of dynamic 1H
NMR analysis, thiazolophane 11 is found to be a conformationally mobile
system. Unfortunately, the conversion of 11 to the title heterophane 2
could not be realized under either photochemical or thermal conditions
<span style="font-size:12.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-ansi-language: EN-IN;mso-fareast-language:EN-IN;mso-bidi-language:AR-SA" lang="EN-IN">Synthesis of <i style="mso-bidi-font-style:normal">anti</i>-[2.2](2.6)benzothiazolophane via 10π-10π: coupling protocol</span>
959-961<span style="font-size:12.0pt;font-family:
" times="" new="" roman";mso-fareast-font-family:"times="" roman";mso-ansi-language:="" en-in;mso-fareast-language:en-in;mso-bidi-language:ar-sa"="" lang="EN-IN">The known
6-methoxymethyl-2-methylbenzothiazole 6
has been converted into quaternary ammonium hydroxide <b style="mso-bidi-font-weight:
normal">4 via demethoxy-bromination followed by quaternization with (CH3)3N
and treatment with silver oxide. Pyrrolysis of <b style="mso-bidi-font-weight:
normal">4, expected to generate both anti-1 and <i style="mso-bidi-font-style:
normal">syn-[2.2](2.6) benzothiazolophane <b style="mso-bidi-font-weight:
normal">2 via 10π-10π couplings of the quinodimethane intermediate
5, gives in practice only anti-benzothiazolophane
1. The structure has been established
by comparison with an authentic sample of 1
recently synthesized by an unambigous route.</span
Donor–acceptor thieno[2,3-b]thiophene systems: synthesis and structural study of 3-anisyl-4-pyridyl(pyridinium) thieno[2,3-b]thiophenes
Synthesis of a new class of cofacially oriented neutral donor–acceptor thienothiophene, namely 3-anisyl-4-pyridyl thieno[2,3-b]thiophenes 7 and its ionic analog 8 has been described to probe the presence of through-space charge transfer interaction. However, structural studies by 1H NMR and UV–visible data indicate at best rather weak charge transfer interaction. The single crystal X-ray analysis of the ionic donor–acceptor thienothiophene 8 reveals many interesting features, i.e. (i) the donor and acceptor rings are not parallel to each other (ii) the interchromophoric distance is much larger (4.08 Å) than the van der Waals distance and (iii) the torsional angle between the pyridinium ring and the thienothiophene is unusually small, being only 38°. These structural features preclude effective through-space charge transfer interaction in 8. Conformational analysis of a model system, 3,4-diphenyl thienothiophene indicated that conformations with reduced torsion between the phenyl rings and the thienothiophene plane are possible to maintain a balance between conjugation and steric congestion and the calculated low energy barrier between the high and low energy conformations of the model system suggest the possibility of aryl ring rotations in peri disubstituted thienothiophenes.
Synthesis, optical spectral studies of photoemmitive benzopyranone crown ether and its application for metal ion extraction
1269-1273Synthesi<span style="color:
#151515;mso-bidi-language:HI">s <span style="color:black;mso-bidi-language:
HI">of a new photoemmitive<span style="color:#151515;mso-bidi-language:
HI">, benzopy<span style="color:black;
mso-bidi-language:HI">ranone 15-crown-5 (1) has been reported starting
from 2-formyl benzo-15- crown-5 by us<span style="color:black;
mso-bidi-language:HI">ing a straightforward protocol. Metal ion extractio<span style="color:black;
mso-bidi-language:HI">n profil<span style="color:#151515;mso-bidi-language:
HI">e revealed 1 to
extract K+ more selectively ov<span style="color:black;
mso-bidi-language:HI">er N<span style="color:#151515;mso-bidi-language:
HI">a+ and Li+ compared to the
known benzo-15-crown-5. However, e<span style="color:black;
mso-bidi-language:HI">xcept f<span style="color:#151515;mso-bidi-language:
HI">or slight
enhancements (8 to 27<span style="color:#151515;
mso-bidi-language:HI">%) <span style="color:black;mso-bidi-language:
HI">in the emission inten<span style="color:#151515;mso-bidi-language:
HI">sities, no
appreciable changes either in the absorption or emission spectra of 1 were
noticeable in the presen<span style="color:#151515;mso-bidi-language:
HI">ce of se<span style="color:black;
mso-bidi-language:HI">lected group I and II metal ions. The
absence of significant optical perturbations <span style="color:#151515;
mso-bidi-language:HI">suggests
at best only weak interaction between the metal
ions and the benzopyranone chromophore<span style="color:#151515;
mso-bidi-language:HI">.
</span
Novel bipolar diaryloxadiazole-benzofuran conjugates: Synthesis, optical, electrochemical and thermal studies
368-373<span style="font-size:9.0pt;mso-bidi-font-size:
8.0pt;font-family:" times="" new="" roman","serif";mso-fareast-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">A
series of diaryloxadiazole chromophores incorporating benzofuran rings of
varying donor characters has been readily synthesized in a one step protocol.
These donor-acceptor-donor systems, designated as <b style="mso-bidi-font-weight:
normal">Benzmox-1-4 exhibit positive solvatochromic behavior and thermal
stabilities in excess of 300°C. From cyclic
voltammetry and emission band data, the HOMO and LUMO energies of Benzmox-1-4 have been calculated to be in the range of 6.43 to
5.65 eV and 2.96 to 3.29 eV, respectively. Of the four chromophoric
systems studied, Benzmox-2 and<span style="mso-bidi-font-weight:
bold"> Benzmox-3 display band gaps of
3.22 and 3.16 eV, and high luminescence efficiency of 0.34 and
0.55, respectively. These features make Benzmox-2 and<b style="mso-bidi-font-weight:
normal"> Benzmox-3 promising
bipolar blue light emitting host materials.</span
Synthesis and structures of thieno[2,3-b]thiophene incorporated [3.3]dithiacyclophanes. Enhanced first hyperpolarizability in an unsymmetrically polarized cyclophane
Dithiacyclophanes incorporating thieno[2,3-b]thiophene have been synthesized. in order to investigate the nonlinear optical properties of donor-acceptor cyclophane 7. Cyclophane 7 displayed significantly higher first hyperpolarizability beta (21.6 x 10(-30) esu) compared to model 10 (9.58 x 10(-30) esu). Relatively higher in 7 presumably arises from an extra electron redistribution arising from through-space charge transfer, a feature lacking in 10. Moreover. the thermal decomposition temperature of 7 (300 degrees C) is higher than that reported for the NLO prototype DAN (295 degrees C). (c) 2006 Elsevier Ltd. All rights reserved