Hole transport in arylamine doped polymers

Fluorescent and charge transport properties of columnar phases made of mono and bi-phenazine derivatives

Mesogenic dibenzophenazine derivatives have been synthesized and their liquid crystalline, fluorescent and electrochemical properties have been studied. All compounds form the Col_hd phase, one of them (4-hydroxyphenyl 2,3,6,7-tetrakisoctyloxy-dibenzo[a,c]phenazine-11-carboxylate, 4) additionally shows an unusual columnar structure with p2mg symmetry, which is a partially lamellarized columnar phase. The emission spectra exhibit a huge Stokes shift that is due to the different molecular conformation in ground and excited states. The non-dispersive hole transport current under UV laser illumination was observed and the charge mobility in the range 10^-4-10^-3 cm² V^-1 s^-1 was determined with the time of flight (ToF) method. The measurements have been interpreted according to the Gaussian disorder model, providing material parameters that reflect the energetic distribution of localized states (diagonal disorder, σ) and distribution of coupling parameters between transport sites (off-diagonal disorder, Σ).

Photochemical properties of multi-azobenzene compounds

A systematic study is reported of the photochemical properties of the multi-azobenzene compounds bis[4-(phenylazo)phenyl]amine (BPAPA) and tris[4-(phenylazo)phenyl]amine (TPAPA) compared to the parent molecule 4-aminoazobenzene (AAB). The bis- and tris-azobenzenes were synthesised by a variant of the Ullmann reaction and exist in their stable all-E forms at room temperature. Striking changes in the spectral positions and intensities of their first ππ* absorption bands compared to AAB reveal strong electronic coupling between the AB units. The nature of the excited states was explored by quantum chemical calculations at the approximate coupled-cluster (CC2) level. Upon UV/VIS irradiation, the molecules isomerise to the Z-isomer (AAB), ZE- and ZZ-isomers (BPAPA), and ZEE-, ZZE- and ZZZ-isomers (TPAPA), respectively. The photoswitching behaviours were investigated by UV/VIS and NMR spectroscopies. All individual isomers were detected by one-dimensional (1D) (1)H NMR spectroscopy (BPAPA) and two-dimensional (2D) HSQC NMR spectroscopy (TPAPA). A kinetic analysis provided the isomer-specific thermal lifetimes. The variance of the thermal lifetimes demonstrates a dependence of the Z-E isomerisation on the chromophore size and number of AB units.