Methylene Blue (This DVD will self-destruct in 48 hours....)

Methylene blue is a well-known dye. It is useful as a biological stain, binds to DNA, and can turn your urine blue.. Incredibly, I'm opting to talk about how it's used in time-sensitive DVDs.

Awhile back, a DVD format called Flexplay was introduced. The idea here is that since DVDs are so relatively cheap to produce, there's no real reason to have the customer return them (except to avoid diluting the value of purchased DVDs). One ill-fated format, DIVX, came about a few years back, but it was unwieldy and essentially a pay-per-view system - special players had to be hooked up to a phone line.

Flexplay attempted to address this problem with chemistry. How successful it is from a business standpoint, I'm not sure - I've never actually seen a Flexplay DVD in the wild, but I digress. We're here to talk about how it works:

Flexplay (and some related systems) are a lot like regular DVDs, but they have a sort of time-bomb feature - they only work for a couple days after you open them. They do this with oxygen-sensitive dyes. Most DVD players (except for the newest ones) use red lasers to read the disc. Flexplay DVDs are much like a regular DVD, but they contain dyes that are colorless until aerially oxidized. One such dye mentioned in the patent is methylene blue - a prodigous absorber of red light. Once the dye's oxidized, it absorbs too much laser light to read properly, and your disc is done. Here's a structure:

The lower structure, with the saturated heteroatoms (nitrogen and sulfur) in the center ring, is called "leucomethylene blue" because it is a member of a broad class of dyes that are colorless until, well, something happens to them. Here, it is an oxidation. Oxygen from the air is enough to oxidize it to the upper structure, which is plain old methylene blue. Colorless leucomethylene blue+Oxygen-> methylene blue -> dead DVD. That simple, right?

Not quite. Judging from the patent, this works a little TOO well, and the leuco dye is oxidized a little too quickly. Solution? Add another step to limit the rate of conversion. To combat this, an organic chemistry technique, broadly referred to as a protecting group is used. The protected leucomethylene blue cannot be oxidized. Normally, you have to set up special reaction conditions to remove a protecting group. Flexplay didn't have that luxury, so they had to work with what was around - in air. Nitrogen's not going to do much, and there arent many air-reactive protecting groups you'd want to use. Fortunately, water is ubiquitous in the atmosphere, so they used a protecting group that reacts with water:

So now, we have TIPSOC-leucomethylene blue + Water -> Leucomethylene blue + Oxygen -> Methylene blue. Apparently, this slows the reaction down enough (and is reproducible enough that the DVD won't last months in dusty Las Vegas, or half an hour in foggy San Francisco).

Not sure how I feel about single-use DVDs, but it's neat chemistry!