Constructing a simple Cone–Chain motif to significantly enhance the first hyperpolarizability of horn-shaped carbon nanocones

According to the density functional theory (DFT) calculations, the first hyperpolarizabilities of the carbon nanocone (CNC)–based systems in a D–π–A framework can be prominently improved by constructing the mixed π-conjugated bridge. The hybrid π-conjugated bridge is constructed by modifying the bottom edge of CNC with –(CHCH)x–NH2/NO2 chain. By connecting the –(CHCH)x–NH2 chain with electron-donating characteristic, the first hyperpolarizabilities of these cone-chain systems can be enhanced more availably, and the substitution position can also play an important role in determining the β0 value. The TDDFT calculations show that building the simple cone-chain motif can effectively improve the degree of charge transfer and reduce the transition energy, thus leading to a considerably large first hyperpolarizability, which is much larger than that of the corresponding directly NH2-decorated CNC system with the same conjugated length. Especially, the first hyperpolarizabilities of these cone-chain motifs (CNC–(CHCH)x–NH2) can increase dramatically with the extension of –(CHCH)x–NH2 chain. Furthermore, in view of the unique horn-shaped structure of CNC, another –(CHCH)x–NH2 chain is added at the bottom edge for double-substitution, and it can further augment the first hyperpolarizability compared with the single-substitution. In addition, the length ratio of cone to chain in the mixed π-conjugate bridge can also have a crucial effect on the β0 value of these cone-chain motifs. Using the –(CHCH)x–NH2 with a comparable conjugated size to modify the bottom edge of cone can be an effective strategy for achieving the remarkable NLO response in the CNC-based system with D–π–A framework. These fascinating findings are advantageous for the design of new high-performance NLO materials based on CNCs.