Energy Band Gap Investigation using First Principle Simulation and Tauc Plot Method of Calixarene and Calixarene-Drug Inclusion Complexes

Abstract

Calixarene has attract attention especially in drug delivery and drug sensor systems due to its peculiar properties, such as functional diversity of the upper and lower rims, hydrophobic cavity, chemical stability, zero toxicity, and controlled release profile. These properties make this supramolecule an ideal candidate for drug encapsulation and sensors. P-aminobenzoic acid (PABA) is a drug in sunscreen which is widely used as a ultraviolet (UV) filter and sunburn protector to protect against solar rays. The calix[n]arene (n=4,6,8) and the host-guest interaction of calix[n]-PABA were characterized using UV–visible spectroscopy and the first-principles pseudopotential method, based on the density functional theory (DFT) and the plane-wave method as implemented into Quantum Espresso code. The DFT calculation is performed to find the estimated calix[n]arene and calix[n]arene-drug band gap. The band gap calculated using DFT has usually underestimated the insulating materials for about 30 – 50% of the experimental gap values, depending on the selected type of exchange-correlation chosen. The optical band gap value of calix[n]arene and calix[n]-PABA obtained from the UV-Visible absorption spectrum estimated using the Tauc plot are then compared with the band gap computed by DFT. The band gap narrowing shown by the complexes indicates that calix[n]arene and PABA reacted. Besides, calix[8]arene is the most promising host in this study since the calix[8]-PABA complex has the most significant binding energy. The band gaps and binding energy results will become a reference for future research in calixarene and calixarene-drug material.