Change in optoelectronic properties of ExBox+4 on functionalization and guest encapsulation

The impact of functionalization as well as guest encapsulation on the optoelectronic properties of the ExBox+4 moiety has been investigated with the aid of density functional theory (DFT) based calculations. To this end, three functionalized variants of the ExBox+4 moiety have been modelled in silico, viz. NH2-ExBox+4-F, CN-ExBox+4-NH2 and NO2-ExBox+4-NH2, whereas coronene (Cor), B-doped coronene (BCor), N-doped coronene (NCor), tetrathiafulvalene (TTF), biphenyl (BiPh), tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) molecules have been employed as guests. The results indicate that as a result of functionalization, the ExBox+4 moiety can exhibit tangible non-linear optical (NLO) response properties as vindicated by the first static hyperpolarizability (β). As a result of guest encapsulation, significant variation in the optoelectronic properties of the chosen hosts takes place. BCor/TCNQ/NCor molecules enhance the NLO activity of the hosts while TTF/TCNE suppresses the same. In particular, NCor@host moieties demonstrate very high β values at the static field limit. Time dependent DFT results suggest that in general, the ability of the guest in tuning the transition energy associated with the pivotal electronic transitions of the host plays the dominant role in the observed variation in β. In addition, BCor/NCor@host moieties demonstrate broadband optical absorption capability thereby elucidating the possibility of deriving multi-purpose optoelectronic features such as NLO activity as well as utility in photovoltaic systems. Thermochemical results suggest that all the guest@host systems are stable at 298.15 K. Non-covalent and electrostatic binding forces stabilize the studied systems.