Reversibly light-modulated dirac point of graphene functionalized with spiropyran.

Graphene has been functionalized with spiropyran (SP), a well-known photochromic molecule. It has been realized with pyrene-modified SP, which has been adsorbed on graphene by π-π interaction between pyrene and graphene. The field-effect transistor (FET) with SP-functionalized graphene exhibited n-doping effect and interesting optoelectronic behaviors. The Dirac point of graphene in the FET could be controlled by light modulation because spiropyran can be reversibly switched between two different conformations, a neutral form (colorless SP) and a charge-separated form (purple colored merocyanine, MC), on UV and visible light irradiation. The MC form is produced during UV light irradiation, inducing the shift of the Dirac point of graphene toward negative gate voltage. The reverse process back to the neutral SP form occurred under visible light irradiation or in darkness, inducing a shift of the Dirac point toward positive gate voltage. The change of the Dirac point by UV and visible light was reproducibly repeated. SP molecules also improved the conductance change in the FET device. Furthermore, dynamics on conversion from MC to SP on graphene was different from that in solution and solid samples with SP-grafted polymer or that on gold nanoparticles.