High selectivity of cyclic tetrapyrrole over tetrafuran and tetrathiophene toward toxic chemicals; A first-principles study

Although, the sensor applications of straight chain conducting polymers are well explored, but, the cyclic analogues are not much explored in this regard. The density functional theory calculations are performed to study the interaction behaviour of tetracyclic oligomers such as tetrapyrrole (4CP), tetrafuran (4CF) and tetrathiophene (4CT) for the detection of harmful gases like, phosgene, thiophosgene and formaldehyde. The most stable interaction configurations, interaction energies (E-int), interaction distance (D-int), SAPTO energies, NCl, NBO charge transfer, HOMO-LUMO gaps and maximum absorbance are evaluated to understand the sensitivity and selectivity of these cyclic analogues toward poisonous gases. The results of all these properties illustrate that 4CP exhibits the highest sensitivity towards analytes with the sequence of formaldehyde > phosgene > thiophosgene. The interaction energies are -10.91, -9.03 and -7.58 kcal mol(-1) for fd@4CP, ph@4CP and tph@4CP complexes, respectively. SAPT0 results depict that the electrostatic forces have strong influence in these complexes which indicate the presence of strong hydrogen bond between 4CP and analytes. However, this is not the case in other oligomer-analyte complexes especially in 4CT based complexes. The highest sensitivity of 4CP enables it to act as promising sensing material for formaldehyde, phosgene and thiophosgene as compared to 4CF and 4CT.