Chemosensor Engineering: Effects of Halogen Attached to Carbon-Carbon Triple Bond Substituent on Absorption energy of Pyridine: DFT-Study

Pyridine, C5H5N, and pyridine derivatives of the structure C5(S)nH5-nN (S = -C≡C-X; X = F, Cl, Br, I) have been studied theoretically using DFT computation employing the B3LYP/LanL2DZ level of theory. Effects of substituent halogenation on electron density enrichment of the pyridine nitrogen, and thus its effectiveness as an electron donor have been investigated. Computational results showed that the substituent halogenation does affect the charge density accumulation on the nitrogen atom of pyridine as well as the C2=N and -C≡C- bond lengths and the C2- N- C6 bond angle. In addition, charge density localization on the nitrogen atom has been found to depend on the number and position of side substituents. Hardness of the halogen atom attached to the tail of the side substituent has been proved to be a determining factor in promoting and qualifying substituted pyridines to act as effective electron donors. The influence of substituent halogenation on electronic localization or delocalization is further viewed by showing (1) charge density distribution surfaces and (2) occupancy of the HOMO molecular orbitals. The conclusions extracted from this investigation support our previous findings in earlier studies through which we attempt to gain more insights toward putting hands on key factors that are anticipated to qualify chelates to be good stabilizers for metal ion complexes that are demanded as chemosensors. Furthermore, this study is considered an important step of progress in our pursued research work that aims to promote inorganic complexes to act as accessible and low energy absorbers. This is essential when inorganic complexes are needed to be employed as colorimertric detectors in the field of chemosensation.