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- Fluorescent bis-calix[4]arene-carbazole conjugates: synthesis and inclusion complexation studies with fullerenes C-60 and C-70Publication . Barata, Patrícia; Costa, Alexandra I.; Costa, Sérgio; Prata, José V.Supramolecular chemistry has become a central theme in chemical and biological sciences over the last decades. Supramolecular structures are being increasingly used in biomedical applications, particularly in devices requiring specific stimuli-responsiveness. Fullerenes, and supramolecular assemblies thereof, have gained great visibility in biomedical sciences and engineering. Sensitive and selective methods are required for the study of their inclusion in complexes in various application fields. With this in mind, two new fluorescent bis-calix[4]arene-carbazole conjugates (4 and 5) have been designed. Herein, their synthesis and ability to behave as specific hosts for fullerenes C-60 and C-70 is described. The optical properties of the novel compounds and their complexes with C-60 and C-70 were thoroughly studied by UV-Vis and steady-state and time-resolved fluorescence spectroscopies. The association constants (K-a) for the complexation of C-60 and C-70 by 4 and 5 were determined by fluorescence techniques. A higher stability was found for the C-70@4 supramolecule (K-a = 5.6 x 10(4) M-1; Delta G = -6.48 kcal/mol). Evidence for the formation of true inclusion complexes between the host 4 and C-60/C-70 was obtained from NMR spectroscopy performed at low temperatures. The experimental findings were fully corroborated by density functional theory (DFT) models performed on the host-guest assemblies (C-60@4 and C-70@4).
- Fluorescent calix[4]arene-carbazole-containing polymers as sensors for nitroaromatic explosivesPublication . Barata, Patrícia; Prata, José VirgílioTwo highly fluorescent calix[4]arene-containing phenylene-alt-ethynylene-carbazolylene polymers (Calix-PPE-CBZs) were used in the detection of explosives from the nitroaromatic compounds (NACs) family, in solution and in vapour phases. Both fluorophores exhibit high sensitivity and selectivity towards NACs detection. The quenching efficiencies in solution, assessed through static Stern-Volmer constants (K-SV), follow the order picric acid (PA) >> 2,4,6-trinitrotoluene (TNT) > 2,4-dinitrotoluene > (2,4-DNT) > nitrobenzene (NB). These correlate very well with the NACs electron affinities, as evaluated from their lowest unoccupied molecular orbitals (LUMOs) energies, indicating a photo-induced electron transfer as the dominant mechanism in fluorescence quenching. Moreover, and most interesting, detection of TNT, 2,4-DNT and NB vapours via thin-films of Calix-PPE-CBZs revealed a remarkably sensitive response to these analytes, comparable to state-of-the-art chemosensors. The study also analyses and compares the current results to previous disclosed data on the detection of NACs by several calix[4]arene-based conjugated polymers and non-polymeric calix[4]arenes-carbazole conjugates, overall highlighting the superior role of calixarene and carbazole structural motifs in NACs' detection performance. Density functional theory (DFT) calculations performed on polymer models were used to support some of the experimental findings.