The gap increases from 3.1 eV (PTI-LiBr) to 3.5 eV (PTI-IF) by VB-EELS. The lower optical gap and band gap of PTI-LiBr can be ascribed to two concomitant mechanisms: (1) the formation of ion pairs (i.e. static dipoles) within the pores from the intercalated species that break the symmetry of the system. Eventually, this leads to the splitting of the degenerate levels at Γ; (2) the presence of intra-optical-gap defect states associated to the p orbitals of Br anion (Figure ). PTI-type intercalation compounds reported hitherto in literature typically show lower optical gaps (2.2-2.7 eV) due to carbonization. The presence of a non-bonding band above the πband (Figure ) is significant as it does not allow for effective carrier injection into the πband. This leads to the absence of the photoluminescence band in the electroluminescence spectrum and, hence, to the defect dominated electroluminescence spectrum as well as the low luminance of the organic light emitting device (OLED). Holes injected into the VB will be trapped due to the nature of the highly localized lone-pair orbitals and recombination will be forbidden. To complement the understanding of the electronic structure with data characterizing the electronic carriers we performed time domain-THz spectroscopy. Intrinsic (i.e. undoped) organic semiconductors typically have a charge carrier density of 10 0 cm -3 and low mobility, as charge carriers are localized at single molecular units leading to hopping as dominant transport mechanism. Nano-crystalline PTI-IF and PTI-LiBr films from nano-crystals typically show low conductivity (PTI-IF 10 -10 S cm -1 , PTI-LiBr 10 -7 S cm -1 ) and only small photo-currents in lateral thin-film devices. To answer the question whether the low conductivity of PTI-films is an intrinsic material property or whether it is induced by the nano-crystalline character of the sample, we subjected free standing pressed pellets of PTI-LiBr and of PTI-IF to time domain-terahertz spectroscopy (THz-TDS) experiments.