How can I easily convert an analog signal to a digital signal?
If your MCU has an on-board comparator that can be configured to generate an interrupt, then you can simply use it. Many MCUs have such functionality. 

Otherwise you can simply add an external comparator such as 1/2 an LM393 or a more modern part if you need very low power. You need a voltage divider to set the threshold- in your case you might use 1.20V (picked because it's exactly between the two levels you mention), so you could use a 1.2K resistor and a 2.1K resistor from the 3.3V supply. You also need a pullup resistor on the output, such as 4.7K. A bit of hysteresis could be added too, but that's outside the scope of this question. 

A 741 won't work in this application- not enough supply voltage, and it can't work to near enough to the supply rails either. Well, if you wanted to give it +/-5V supplies and add a transistor after it to provide 3.3V logic levels you could force it to work (but it would work-to-rule, which is slowly)-- that's a bit silly.