2,3,7, 8,12,13-Hexakis[2-(2-methoxyethoxy)ethoxy]-tricycloquinazoline: a discogen which allows enhanced levels of n-doping

A synthesis has been developed for 2,3,7,8, 12,13-hexakis[2-( 2-methoxyethoxy) ethoxy]-tricycloquinazoline ( TCQ6EO2M) in which the ethylenoxy side chains are introduced before elaboration of the heterocylic core. This discogen gives a hexagonal columnar phase (Col(h)) between 77 and 233 degreesC. n-Doping using potassium metal is facilitated firstly by the electron poor/pi -defficient nature of the core and secondly by the polyethylenoxy side chains which complex the potassium K+ counter-ions. The conductivity of the Col(h) phase of TCQ6EO2M doped with 10 mol% potassium (sigma (parallel to) = 1.1 x 10(-3) S m(-1)) is substantially higher than that previously reported for 2,3,7,8, 12,13-hexa(hexylthio) tricycloquinazoline doped with 6 mol% potassium (sigma (parallel to) = 2.9 x 10(-5) S m(-1)). Photoconductivity studies of TCQ6EO2M using a time of flight sample configuration show transient photocurrents for both holes and electrons. From these an upper limit on the mobility for the electrons is estimated as similar to 10(-4) cm(2) V-1 s(-1) at 150 degreesC which is of the same magnitude as that for hole mobilities in other columnar discotic liquid crystals.