Molecular fluorescence from H₂TBP porphyrin film on Ag substrate excited by tunneling electrons

Molecular fluorescence from H₂TBP porphyrin (H₂TBPP) films on Ag substrate is excited by a scanning tunneling microscope (STM) at ambient conditions. The molecular films are prepared by spin-casting method. The thickness of films can be controlled by the times of dropping H₂TBPP solution. Molecular fluorescence of as-above prepared H₂TBPP films with 4-14 nm thickness at both polarities of applied bias voltage are well defined in good matching with its photoluminescence spectrum, which suggests the same decay channel associated with the HOMO-LUMO radiative transitions similar to H₂TBPP/Au. The thickness dependence of light emission intensity of molecular fluorescence has been studied. The results show that for thicker film, molecular fluoresceence tends to be much stronger due to the effective decoupling of the emitter from the metal substrate.