TDDFT investigation of electronic and optical properties of diaryl-substituted naphtho[1,2-d:5,6-d′]bis-(oxaphosphole) compounds

Abstract

Density functional theory (DFT) and time-dependent DFT calculations using the CAM-B3LYP functional were performed to investigate the electronic and optical properties of 2,7-Ph2-naphtho[1,2-d:5,6-d′]bis-(oxaphosphole) (Ph2-NBOP). Furthermore, we examined the effect of several structural modifications of Ph2-NBOP on the energy gap between the highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO, respectively). The HOMO-LUMO gap (ΔEH-L) can be tuned by controlling the π-orbital overlap. Substituting As for P hinders the effective π-orbital overlap due to the inherently different size of pz orbitals perpendicular to the molecular plane, and results in a decrease of ΔEH-L (5.58 eV) than that (5.79 eV) of Ph2-NBOP. Moreover, asymmetric addition of substituents to the terminal phenyl ring increases the polarization of P or As, leading to a decrease in ΔEH-L due to the more ionic character of the corresponding bonds. Based on these results, we designed a minimal ΔEH-L model (CN1(NH2)1-NBOAs), P atoms of Ph2-NBOP are replaced to As and both CN and NH2 are attached to the terminal points of the phenyl rings of Ph2-NBOP, whose ΔEH-L (4.88 eV) is almost 1 eV smaller than that (5.79 eV) of Ph2-NBOP.