Your last sentence doesn't make sense. Bromo-Dragonfly doesn't mainly have long duration because of the bromo-atom / bromo-moiety / bromo-group (NOT bromo-molecule), it has a long duration for other reasons, but mainly the alpha-methyl group on the far right which prevents it from being broken down sooner. It is not only what makes it last a lot longer but also a lot more potent than the drug 2C-B-Fly which is identical only without that alpha-methyl.
The alpha methyl is what makes this one a substituted amphetamine, on top of a substituted phenethylamine.
Other than that the occurrence of the bromo-group is purely coincidental, just like bromazepam has nothing to do with any of this. It is just one of many parts of the molecule and as far as the drug's actions due to pharmacology go, the entire molecule and in what receptors can fit is concerned as the whole sum of parts, not just simply the separate parts.
There is an article with basically a report on 5-bromo-DMT somewhere, I'll have a look if I can find it really quickly.
Despite what I explained, it seems the 5-Bromo group on 5-Br-DMT could make it more potent and longer acting because again it is probably not broken down as easily or quickly as DMT itself. The reason for this is probably that it doesn't fit as well in the enzyme that is supposed to break it down.
That the bromo group is responsible for it here is - I must make clear again - kind of coincidental, it could have just as easily been a 5-MeO group and indeed a methoxy on the very same position has a similar effect on metabolism.
But it also makes it a differently acting substance. Not because of how it is broken down but how it fits in receptors. 5-MeO-DMT does a lot of other stuff DMT does not, just like 5-Br-DMT can be a bit different.
edit: here it is:
http://www.vice.com/read/sea-dmt-000481-v20n3
