Efficient electrophosphorescence from a platinum metallopolyyne featuring a 2,7-carbazole chromophore

The synthesis, thermal and emission properties of an electrophosphorescent platinum (II) metallopolyyne polymer consisting of 9-butylcarbazole-2,7-diyl spacer P1 are described. The optical and electronic properties of P1 are compared to their molecular diplatinum (II) and digold (I) model complexes. The photophysical properties of P1 are somehow analogous to its 2,7-fluorene-linked congener but differs significantly from that for the 3,6-carbazole derivative. Its optical band gap is notably reduced as compared to that for the 3,6-carbazole analog. Multi-layer polymer light-emitting diodes (PLEDs) were fabricated with P1 as the emitting layer which gave a strong green-yellow electrophosphorescence. The best PLED can reach the maximum current efficiency of 4.7 cd. A^-1 at 5 wt.-% doping level, corresponding to an external quantum efficiency of 1.5%. This represents the first literature example of efficient PLEDs exhibiting pure triplet emission under electrical excitation for metallopolyynes without the concomitant singlet emission. For safety concern, this was also tested for possible cytotoxicity and it does not show significant cytotoxic activity on liver and breast derived human cells at reasonable doses, rendering this functional material safe to use in practical devices.