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


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


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.


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