External electric field driven conformation of the wing-shaped nanographene to close: enhancing and tuning nonlinear optical properties

The nanographene has attracted intensive research interest due to its unique structure and remarkable proper-ties. In the present work, we applied the external electric field (F & PLUSMN; z) to the wing-shaped N-doped nanographene with the bicyclo[2.2.2]-octadiene(BCOD)-bridged bis-hexapyrrolohex-aazacoronene (HPHAC), the BCOD-HPHAC in the direction of the negative and the positive z-axis, respectively. Interestingly, the geometric structures of the BCOD-HPHAC are from patulous to closed under the F & PLUSMN; z, the centrosymmetric symmetry of system is broken. Further, the molecular electrostatic potential (ESP) maps show that the F & PLUSMN; z can effectively regulate the charge distribution of the BCOD-HPHAC. Markedly, the first hyperpolarizabilities (& beta;tot) are regulated efficiently under the F & PLUSMN; z. Compared with the F-z, the Fz induces a larger & beta;tot value of ranging from 2.07 x 102 au (F & PLUSMN; z = 0 au) to 1.01 x 104 au (Fz = 200 x 10-4 au). Moreover, the evolutions of the absorption spectra can explain well the trend of & beta;tot values under the F & PLUSMN; z. We hope that the current work can inspire the investigations of the centrosymmetric nanographenes in the field of NLO response controlled by the external electric field.