Vibrancy of chocolate sauce dessert chefs,

I make chocolate sauce for my drinks. My recipe is, in order, 1x unsweetened bakers chocolate (whole bar, chopped), 3x water, heat, 2.5x brown sugar, dash of salt, vanilla, strain. Transfer to mason jar, and allow to heat seal. 

I use it on the first day and the freshness is just bursting -- the flavor seems to impart up to the inner nostrils.

My problem is that on the second day, the vibrancy, the inner nostril sensations, seem to fade, though the chocolate flavor is still there of course. 

Is chocolate really this delicate and fickle? Is there something wrong with my recipe, solvent used?

A barista in a popular cafe in Manhattan told me that their chocolate sauce is brought daily to the store. Pretty costly operation for chocolate, IMO.
There is nothing wrong with your recipe. This is not only typical, it can't be changed. 

The human sense of smell is triggered by molecules floating in the air we breathe. When you make a chocolate sauce, some of its molecules are volatile - that is, not very attached to the sauce, ready to leave the surface and float off into the air like a helium balloon when a gust of wind tears its string - and others (most of them) are not, they stay put where they are. 

The volatile molecules get into the air, we breathe them in and so we smell the chocolate. But after some time, all the ones which were volatile to begin with have floated away, and are not any longer there. 

The other thing which is happening are probably some chemical reactions. I am not sure of the details, but with something as complex as chocolate, there has to be a bit of degradation going on. With chocolate being so stable over long periods of time, I'd say this contributes much less to the effect, but I am adding it here for thoroughness. 

So there is nothing to be done. If you try to somehow "anchor" the smell molecules to the chocolate, they won't go away, but they won't be available for being smelled either. Either way, you cannot get the smell to linger. If you want sauce which smells fresh, you have to make it fresh.