Optical properties of bilayer quantum dot models based on coronene and its BN analogues with a BODIPY dye: Theoretical TD-CAM-B3LYP-D3 investigation.

Abstract

Quantum dots (QD) belong to a class of materials considered technologically important for their tunable absorption and emission properties and a huge application potential in optoelectronic technologies. To date, only simplified monolayer models of QDs and their dimers have been considered when modeling their absorption and/or emission spectra and effects of edge functionalization. Here, we analyze the optical properties of new type electron donor-acceptor bilayer quantum dot models based on coronene and its boron-nitride analogues (electron donors) with a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene dye (Bdp, an electron acceptor) dye by using time-dependent density functional theory. To understand the nature of transition shifts in electronic spectra, we use BN models with strong modification of the HOMO and LUMO: m-BNC (middle hexagonal ring CC bonds are substituted by BN), p-BNC (all peripheral CC bonds are substituted by BN), and f-BNC (all C atoms are replaced by B and N in an alternate manner). Adiabatic ionization potentials of all coronenes were also calculated. The obtained results show that significant interlayer charge transfer (CT) on excitation of bilayer QDs in S1, S2, and S3 states from strong electron donors, coronene (6.93 eV) and m-BNC (6.52 eV), to Bdp will occur. As a result, one can observe only very weak absorption of CT-character in the low-energy spectrum region as well as strong fluorescence quenching of Bdp. On the contrary, for the weak electron donors, p-BNC (7.22 eV) and f-BNC (8.22 eV), strong Bdp-like absorption and fluorescence bands of local excitation character in the low-energy region are expected. Correlation of optical properties of bilayer QDs with ionization potentials of coronene monolayers has been founded. The obtained results can be useful for future graphene-based optoelectronic applications.