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/LanL2DZlevel of theory. Effects of substituent halogenation on electron density enrichment of the pyridinenitrogen, and thus its effectiveness as an electron donor have been investigated. Computationalresults showed that the substituent halogenation does affect the charge density accumulation onthe nitrogen atom of pyridine as well as the C2=N and -C≡C- bond lengths and the C2 NC6 bond angle. In addition, charge density localization on the nitrogen atom has been found todepend on the number and position of side substituents.Hardness of the halogen atom attached to the tail of the side substituent has been provedto be a determining factor in promoting and qualifying substituted pyridines to act as effectiveelectron donors. The influence of substituent halogenation on electronic localization ordelocalization is further viewed by showing (1) charge density distribution surfaces and (2)occupancy of the HOMO molecular orbitals. The conclusions extracted from this investigationsupport our previous findings in earlier studies through which we attempt to gain more insightstoward putting hands on key factors that are anticipated to qualify chelates to be good stabilizersfor metal ion complexes that are demanded as chemosensors. Furthermore, this study isconsidered an important step of progress in our pursued research work that aims to promoteinorganic complexes to act as accessible and low energy absorbers. This is essential wheninorganic complexes are needed to be employed as colorimertric detectors in the field ofchemosensation.