Graphene/polythiophene composites are widely used in a variety of optoelectronic devices and applications, e.g., as electrode materials in capacitors and solar cells, but the detailed molecular-level relationship between their structural and electronic properties is not well understood. We present a density functional theory study of these composites using model systems consisting of graphene nanosheets and nanoribbons sandwiched between oligothiophenes (up to 13 monomers in length). These systems are investigated by computing optical band gaps, UV− visible spectra, densities of states, and by analyzing noncovalent interactions in terms of the reduced density gradient. Frontier molecular orbital analysis reveals a significant decrease in the optical band gap upon increasing the concentration of graphene, which can be tuned by adjusting the proportion of graphene using larger nanoribbons. This finding has implications for device design in these materials.

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Graphene composite of polyaniline (PANI) emeraldine salt is systematically studied to explain its experimentally observed enhanced sensitivity for methylamine and ammonia as compared with simple PANI emeraldine salt conducting polymer sensor. The interaction behavior is studied with M062X method of density functional theory. Optimization of geometries, calculation of interaction energies, and natural bond orbital charge analyses are performed to study and explain the sensing behavior. Charge analysis is performed to know the magnitude and direction of electronic charge flow during sensing phenomenon. Frontier orbitals interaction theory is used to compare the strength of interaction of analytes with simple and composite sensors. The selectivity of both sensors toward analytes is also verified using the same theory. Absorption behavior of simple and composite sensors against incident electromagnetic radiations is also studied before and after sensing. Non-covalent interaction analysis is performed to identify and distinguish different types of attractive and repulsive forces present within addition products. It is concluded that graphene composited PANI sensor shows greater sensitivity toward considered analytes as compared with PANI emeraldine salt sensor and this outcome is in agreement with reported results based on experimental observations. The better efficiency of composite sensor is due to direct interaction of analytes with graphene in addition to their interaction with PANI conducting polymer.

Composite formation with graphene is an effective approach to increase the sensitivity of polythiophene (nPT) gas sensors. The interaction mechanism between gaseous analytes and graphene/nPT composite systems is still not clear, and density functional theory calculations are used to explore the interaction mechanism between graphene/nPT 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/nPT nanoribbon composite materials for gas sensors.