New zinc phthalocyanine derivatives for nitrogen dioxide sensors: A theoretical optoelectronic investigation.

Zinc-phthalocyanines ZnPc derivatives including quinoleinoxy groups have been studied through DFT calculations. The most stable geometries were characterized for the unsubstituted to the tetra substituted ZnPcs. The energy gap decreased from 2.146 eV for ZnPc to 2.050 eV for ZnPcR, in agreement with the experimental trend, and indicating the reliability of the electrochemical evaluation of LUMO and HOMO energy levels. Optical transitions computed at the CAM-B3LYP-D3 with triple zeta basis sets were found to be in good agreement with experimental values for both the B and Q bands. Subsequently, structures were also characterized for NO adsorbed complexes, in order to assess the potential role of ZnPc as a NO sensor. A clear sigma bonding chemisorption of NO on Zn atom is observed for all derivatives, followed by a charge transfer from the π Pc conjugated system to the Zn-NO moiety. More importantly, after NO chemisorption on ZnPc derivative a remarkable red-shift is observed in the optical spectra, particularly for NO/ZnPcR complex, thus offering a good index to detect the binding of NO. The optical spectra and the vibrational spectra can therefore be used to detect the presence of NO and ZnPc derivatives show appropriate properties to constitute good NO sensors.