The electronic and magnetic properties of polyacenes become quite fascinating as the number of linearly conjugated benzene rings increases. Higher-order conjugated polyacenes develop radicaloid characters due to the transition of electronic structures from closed-shell to the open-shell system. Here we have investigated the role of such polyacenes as the magnetic coupler when placed between the two spin-sources based on nitroxy radicals. To do so, the magnetic exchange interactions (2J) are computed employing broken-symmetry (BS) approach within the density functional theory (DFT). In this approach, various genre of exchange- correlation (XC) functionals such as generalized gradient approximation (GGA), meta-GGA, hybrid functional, constrained spin density (i.e. CDFT) and on-site Coulomb correlation corrected GGA + U functionals are adopted. All DFT based calculations estimate an exponential increase in 2J values with the length of the couplers. This observation has been understood in terms of increase in number of near-degenerate or quasi-degenerate molecular orbitals (MOs), reduction of HOMO-LUMO energy gap and descend of low-lying excited states as the number of fused benzene rings are increased.
We are working at the Institute of Nano Science and Technology Mohali, one of the leading research institutes in India in the field of Nano Science. INST is located in Chandigarh, one of the major cities of India.