Quantum chemical study on sensing of NH3, NF3, NCl3 and NBr3 by using cyclic tetrapyrrole

Toxic gas sensors with ultrahigh sensitivity are highly desirable and those can be achieved with the help of infinite it-conjugation of cyclic conducting polymers. In this DFT study, we demonstrate the adsorption performance of tetracyclic oligopyrrole (CTPy) towards NH3 and nitrogen halides including NF3, NCl3 and NBr3. The CTPy possesses infinite conjugation and highly active cavity which provides an excellent platform for the adsorption of upcoming gas molecules. Thermodynamically, the observed interaction energies of NH3, NF3, NCl3 and NBr3 analytes with CTPy at coB97XD/6-31+G(d,p) level of theory are -13.14, -3.00, -6.00 and -7.50 kcal/ mol, respectively. In addition, the molecular dynamic simulations are performed at GFN2-xTB method to confirm the stability of CTPy and respective complexes. The SAPT0 and NCI analyses reveal that dispersion forces play a significant role to stablize these complexes. Moreover, the electrostatic component also contributes in stabilizing the NH3@CTPy, NCl3@CTPy and NBr3@CTPy complexes. The variation in the electronic properties including HOMO-LUMO gaps of complexes along with the significant NBO charge transfer indicate the increasing conductivity of CTPy upon complexation with reported analytes. The prominent charge transfer on interaction might be due to the increasing it to it* transition, thus the ?max is shifted to longer wavelength in UV?vis spectra.