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We investigate p-type doping of polys9,9-dioctylfluorenyl-2,7-diyld (PFO) films with tetrafluorotetracyanoquinodimethane (F4-TCNQ) introduced via cosolution. Doped and undoped films are compared using ultraviolet photoelectron spectroscopy (UPS) and current-voltage (I-V) measurement. In spite of the difference between the ionization energy of PFO (5.8 eV) and the electron affinity of F4-TCNQ (5.24 eV), p doping occurs, as seen from the movement of the Fermi level (EF) toward the polymer highest occupied molecular orbital (HOMO). Interface hole barriers are measured for undoped and doped PFO deposited on three substrates with different work functions, indium-tin-oxide (ITO), gold (Au), and poly-3,4- ethylenedioxythiophene.polystyrenesulfonate (PEDOT.PSS). Doping leads to the formation of a depletion region at the PFO/ITO and PFO/Au interfaces. The depletion region is believed to be at the origin of the sholed current enhancement observed on simple metal/PFO/substrate devices. [ABSTRACT FROM AUTHOR]

A series of silole molecules with fluorenyl substituents at varying positions—1-(9,9-dimethylfluoren-2-yl)-1,2,3,4,5-pentaphenylsilole, 1-(fluoren-9-yl)-1,2,3,4,5-pentaphenylsilole, 1,1,3,4-tetraphenyl-2,5-bis(9,9-dimethylfluoren-2-yl)silole, and 1,1-diphenyl-2,3,4,5-tetrakis(9,9-dimethylfluoren-2-yl)silole—has been synthesized and compared to the previously reported compounds, 1,1,2,3,4,5-hexaphenylsilole and 1,1-bis(9,9-dimethylfluoren-2-yl)-2,3,4,5-tetraphenylsilole. The effect of fluorenyl substitution pattern on the geometric, thermal, electronic, optical, and electroluminescence properties was investigated both experimentally and theoretically. Analysis of the X-ray crystal packing diagrams for two new fluorenyl-substituted siloles indicates the presence of π–π stacking and CH⋯π interactions in the solid state. Across the series, excellent thermal and morphological stabilities are displayed. Photoelectron/inverse-photoelectron spectroscopy measurements and density functional theory (DFT) calculations suggest that increased conjugation length through substitution at the 2- and 5-positions plays a more significant role in tuning the ionization potentials and electron affinities of these siloles than do inductive effects through substitution of the silicon. The electronic structure (e.g., HOMO–LUMO gap) and, hence, the optical absorption and fluorescence properties are also sensitive to the positions at which the fluorenyl groups are introduced, with substitution at the 2,5-positions having the largest effect. Solution-processed electroluminescent devices fabricated with the fluorenyl-substituted siloles as the emissive layer have luminous efficiencies as high as 3.6 cd A−1. [ABSTRACT FROM AUTHOR]