Absorption properties of a BODIPY-curved graphene nanoflake system: A theoretical investigation.

Abstract

Modifications in the electronic transitions of a popular 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (boron dipyrromethene, BODIPY) dye caused by quasi-parallel stacking with corannulene (C) were studied by means of time-dependent density functional theory (TD-DFT) with the CAM-B3LYP functional. The effects of the electron-withdrawing (CN) and electron-donating (NH2) substituents at the meso (8) position in the BODIPY core and the corannulene rim position on the character, location, and oscillator strengths (f) of some transitions of complexes were also discussed. To understand better the nature of the transitions, their occupied and virtual orbitals involved into the first electronic transitions as well as the electron density difference plots between excited and ground states of the complexes were investigated. The S0 → S1 transitions of 8H-B/C and 8NH2-B/C complexes have a small admixture of the charge transfer (CT) character in direction from BODIPY to corannulene (B → C). They located at 2.80 and 3.11 eV, respectively, and have f of ∼0.15. The 8CN-B/C complex with a stronger acceptor BODIPY part has the S0 → S1 transition with a higher degree of CT (B → C) at 2.32 eV with f = 0.08. The 8H-B/2NH2-C complex with a stronger donor corannulene part has the S0 → S1 transition with an expressed CT(B → C)-character at 2.58 eV with f = 0.003, whereas the S0 → S2 transition acquires in a some extent the features of the LE(B → B) character. A much interesting situation exists in the case of the 8NH2-B/2CN-C complex. Here we can find both CT (B → C) and CT (C → B) among the first five states. Besides this, different, higher in energy CT states and states delocalized on both molecules were observed.