Nonlinear optical and charge transfer properties of tetracene adsorbed on silver: A DFT approach

Abstract

Charge transfer properties and adsorption mechanism of tetracene on silver are investigated based on DFT and SERS. Optimized geometries indicate distortions in hexagonal structure and deviations in co-planarity of carbon atoms due to the variations in bond angles and dihedral angles after adsorption on silver. Natural population analysis (NPA) confirms the charge transfers from silver to tetracene. Natural bond orbital (NBO) analysis illustrates the overlapping of π(CC) and π*(CC) orbitals and that of Ag valence orbitals with π(CC) of tetracene indicating charge transfers consequent to the process of adsorption. Theoretically simulated absorption spectrum has a surface plasmon resonance peak around 520nm with major contributions arising from the charge transfers from HOMO to LUMO, HOMO-1 to LUMO and HOMO to LUMO+2 excitations. Theoretically predicted SERS confirms the tilted orientation of tetracene on silver surface and the charge transfers reported. Chemically reactive sites were identified through Fukui functions. Localization of electron density arising from redistribution of electrostatic potential along with the reduction in bandgap of tetracene after adsorption on silver suggests its utility in the design of electro active organic semiconducting devices. Enhancement in dipole moment, polarizability and hyperpolarizability of tetracene after adsorption on silver indicates its potential in the design of novel NLO materials.