Comparing the distribution of the electronic gap of an organic molecule with its photoluminescence spectrum

The electronic gap structure of the organic molecule N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine, also known as TPD, has been studied by means of a Scanning Tunneling Microscope (STM) and by Photoluminescence (PL) analysis. Hundreds of current-voltage characteristics measured at different spots of the sample show the typical behavior of a semiconductor. The analysis of the curves allows to construct a gap distribution histogram which reassembles the PL spectrum of this compound. This analysis demonstrates that STM can give relevant information, not only related to the expected value of a semiconductor gap but also on its distribution which affects its physical properties such as its PL.

We acknowledge financial support of the Spanish Government (Grant Nos. FIS2010-21883-C02-01, MAT2011-28167-C02-01, and No. CONSOLIDER CSD2007-0010) and Comunidad Valenciana (ACOMP/2012/127 and PROMETEO/2012/011). This research has been partial funded by FEDER funds of the EU.