Design of Novel Alkali Metals (Li, Na, K) Doped [6] Cycloparaphenylenes with High Nonlinear Optical Response

Abstract

Nonlinear optical (NLO) materials have gained tremendous attention because of their vast applications in different fields such as optoelectronics, telecommunication and data storage etc. In this work, geometric, electronic, linear and nonlinear optical properties of alkali metals (Li, Na and K) doped cyclic organic systems i.e., [6] cycloparaphenylene ([6]CPP) and methylene bridged [6] cycloparaphenylene (MB[6]CPP) are investigated via density functional theory (DFT). The diffuse excess electrons generated by alkali metals have significantly tuned their electro-optical properties. The alkali metals doped CPP based complexes have exhibited a large thermodynamic stability up to -32.1 kcal/mol. Moreover, reduction in HOMO-LUMO (H-L) energy gap has been observed up to 2.92 eV because of the generation of new HOMO which is further confirmed by density of state (DOS) analysis. The NBO analysis has revealed the charge transfer from metals to the CPPs. In addition, NCI and QTAIM analyses have exploited the nature of intramolecular interactions. Doping of alkali metal atoms significantly has increased the first hyperpolarizability (βₒ) of all the complexes. The K@r6-[6]CPP has exhibited the highest hyperpolarizability value of 1.10 x 107 au. Moreover, the absorption spectra have revealed the bathochromic shift for the alkali metals doped complexes. Furthermore, the frequency dependent first hyperpolarizability calculations have been done for M@r6 doped [6]CPP and MB[6]CPP at two routinely used frequencies (532 nm and 1064 nm). The results have shown that the highest response of both SHG (2.25 × 107 au) and EOPE (2.81 × 106 au) are obtained for K@r6-[6]CPP at 1064 nm. These fascinating results will be helpful to utilize the designed [6]CPP and MB[6]CPP based complexes for the generation of advanced optoelectronic devices and high performance NLO materials.