Semiempirical study on the absorption spectra of the coronene-like molecular models of graphene quantum dots.

Affiliation

Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Electronic address: [Email]

Abstract

Polycyclic aromatic hydrocarbons of the general formula C6n2H6n (coronene family) were used as molecular models of graphene quantum dots (GQDs). Absorption spectra of the model compounds were calculated by ZINDO/S method. The S0 → S1 transition energy (E1) was found to decrease with n as E1 = 4.75 × n-0.633 eV. This transition is forbidden in symmetric compounds but 'switches on' upon symmetry breaking. The energy of the first bright optical peak (Ebr) was found to decrease with n as Ebr = 6.31 × n-0.6 eV. The data obtained corroborate the earlier finding that the size-independent optical properties of GQDs are determined by relatively small isolated sp2 clusters separated by sp3 (oxygen-contained) 'defects' rather than the whole (corrupted) graphene sheets; such nanoparticles actually are not quantum dots. GQDs of pure (without defects) graphene sheets with fully π-conjugated sp2 systems should exhibit size-dependent optical properties due to the quantum confinement effect.

Keywords

Absorption,Cluster,Coronene,Graphene quantum dot,ZINDO/S,