No abstract

Diphenyldiazomethane with four iodine groups at the ortho positions and two tert-butyl groups at the para positions, i.e., bis(4-tert-butyl-2,6-diiodophenyl)diazomethane (1a-N 2 ), was synthesized as a sterically hindered triplet carbene precursor. Irradiation of 1a-N 2 in solution effectively generated the corresponding triplet diphenylcarbene 3 1a, which was characterized by UV-vis spectroscopy at low temperature, along with laser flash photolysis techniques at room temperature. The UV-vis spectrum of 3 1a was obtained by irradiating 1a-N 2 in a 2-methyltetrahydrofuran matrix at 77 K. The ESR spectrum showed no triplet carbene signals, while a radical species was observed at the anticipated temperature of the decomposition of triplet carbene 3 1a. Transient absorption bands ascribable to 3 1a were observed by laser flash photolysis of 1a-N 2 in a degassed benzene solution and decayed very slowly with a second-order rate constant (2k/εl) of 5.5 × 10 −3 ·s −1 . Steady-state irradiation of 1a-N 2 in degassed benzene afforded 9,10-diarylphenanthrene derivative 2a in a 31% yield. Triplet carbene 3 1a was also trapped by either oxygen (k O2 = 6.5 × 10 5 M −1 ·s −1 ) or 1,4-cyclohexadiene (k CHD = 1.5 M −1 ·s −1 ) to afford the corresponding ketone 1a-O or the diarylmethane 1a-H 2 . The carbene was shown to be much less reactive than the triplet diphenylcarbene that is protected by two ortho-iodo and two ortho-bromo groups, 3 1b.

The photoquenching effect of electroluminescence (EL) has been observed for the first time in thin-film ZnS:TbF3 EL devices. The luminescent intensity and the conductive charge are quenched, when the device is exposed to a visible light of energy between 1.75–2.75 eV. The maximum photoquenching rate of 45% is observed at a voltage slightly higher than the EL threshold voltage. The recovering time from the photoquenching is of the order of several seconds. This photoquenching effect is likely to be due to deep hole traps.