Theoretical Approach to Evaluate the Gas-Sensing Performance of Graphene Nanoribbon/Oligothiophene Composites.

Composite formation with graphene is an effective approach to increase the sensitivity of polythiophene ( n PT) gas sensors. The interaction mechanism between gaseous analytes and graphene/ n PT composite systems is still not clear, and density functional theory calculations are used to explore the interaction mechanism between graphene/ n PT nanoribbon composites (with n = 3-9 thiophene units) and gaseous analytes CO, NH 3 , SO 2 , and NO 2 . For the studied analytes, the interaction energy ranges from -44.28 kcal/mol for (C 54 H 30 -3PT)-NO 2 to -2.37 kcal/mol for (C 54 H 30 -3PT)-CO at the counterpoise-corrected ωB97M-V/def2-TZVPD level of theory. The sensing mechanism is further evaluated by geometric analysis, ultraviolet-visible spectroscopy, density of-states analysis, calculation of global reactivity indices, and both frontier and natural bond orbital analyses. The variation in the highest occupied molecular orbital/lowest unoccupied molecular orbital gap of the composite indicates the change in conductivity upon complexation with the analyte. Energy decomposition analysis reveals that dispersion and charge transfer make the largest contributions to the interaction energy. The graphene/oligothiophene composite is more sensitive toward these analytes than either component taken alone due to larger changes in the orbital gap. The computational framework established in the present work can be used to evaluate and design graphene/ n PT nanoribbon composite materials for gas sensors.