Abstract
The sensitivity of 5, 10, 15, 20-tetraphenylporphyrin (H2TPP) to the presence of NO2 gas in diluted solutions and in Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) films was investigated by UV-visible spectroscopy. The shift of Soret and Q bands were analyzed and the energies involved were calculated. The exposure of LB porphyrin films deposited onto glass slides to NO2 has performed as an active chemsensor with 7000 ppm gas concentration. Furthermore, the UV-vis dichroism absorption results associated with the Soret bands have given evidence of the tilt angle of the macrocycle related to the substrate. H2TPP in LB film was tilted by an angle of 51 ± 5° and in the LS film was tilted by an angle of 36° ± 5° indicating the formation of a preferential organization of the molecular films depending on the deposition method.
Highlights
Tetraphenyl porphyrins or H2TPP are the simplest porphyrins which have been investigated
Considering the uncertainty of ± 5° that comes from the polarized UV–vis method[2], the results indicated that the macrocycle of H TPP in LB film was tilted by an angle of 51 ± 5° and in the LS film was tilted by an angle of 36 ± 5° (Figure 9)
The response of 5, 10, 15, 20-tetraphenylporphyrin to the presence of NO2 gas in diluted solutions and in Langmuir-Blodgett and Langmuir-Schaefer films was verified by UV-visible spectroscopy based upon the shift of Soret and Q bands
Summary
Tetraphenyl porphyrins or H2TPP are the simplest porphyrins which have been investigated. These porphyrins yield isotherms with an extrapolated area of only 13-17 Å2 per molecule[1] This contrasts with an expected value of 225 Å2 per molecule, if the molecules lie flat on the water surface, and with an expected value of 90 Å2 per molecule for a vertical packing array of molecules[2]. For these macrocyclic molecules, organized supramolecular structures can be formed in monolayers. The presence of double-conjugated bonds attributes the sp[2] planar configuration with several possibilities of π-π* transitions These structures, referred to as a playing-card model, have been confirmed by AFM measurements of Langmuir and self-assembled monolayers of porphyrins and phthalocyanines[2]. The limitation of 3D conformation due to the planar structure restricts the overall mobility on reaching a thermodynamic energy minimum
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