Electronic structure of organic films in the first excited states determined using scanning tunneling spectroscopy: An experimental and theoretical study

We report a pilot study of whether laser-assisted scanning tunneling spectroscopy (STS) can be used to investigate the changes in electronic structure between the ground state and first singlet (S-1) excited states of thin films of organic molecules. STS measurements of 4",3"-dimethylsexithiophene and pentacene, excited into their S-1 states using suitable continuous wave laser excitation, show a narrowing of the electronic gap. These results are consistent with theoretical calculations of the electronic structure of these molecules in their S-1 states.