How to use voltage divider between ESP8266 (3.3v) and IR proximity sensor (5V)?
My experience with esp8266 tells me that if you power esp8266 with a 3.3V supply and you provide 5V/0V signal to its pins (either Tx/Rx or pin0,1) nothing's gonna happen. It will work fine.

Based on this experience, i would like to suggest you to 


power your esp8266 with 3.3V pin of your TTL converter
power your IR sensor using 5V output pin of your TTL converter
connect signal pin of IR sensor to your esp8266 digital pin. (just
in case esp8266 heats up, disconnect circuit and try using voltage
divided only for this particular connection.


If using those external power supplies don't forget to common GND (or -ive terminal) of those power supplies.