Hi Michael,
As the '4093 is a NAND gate, the ouput will be inverted, how are you driving the IR LED?
If you have a two channel 'scope, put 1 channel on your data from the PIC and the other on the output of the '4093. You should see a high level when your data is low and a series of low pulses when the data is high.

HTH,
Robert G8RPI.