shirt tie jacket

There are two reasons it looks bad in my opinion.
Reason one is historical / aesthetical. Shirts are basically underwear, and thus traditional etiquette requires them to be covered in public situations. Also, since dress shirts are bright and plain or modestly patterned, they even look like underwear, unsexy and "naked" without a jacket or a vest.
Reason two is social. Dress shirts without a jacket is the "don't care" uniform of corporate bottomfeeders. A tie only makes it worse, giving you the stiffness of a formal attire without the dignity. One might as well tattoo "wage slave" on his forehead.
My personal philosophy is, either be a rebel or a lord. Wearing a dress shirt with a tie and no jacket is neither rebel nor lord. It's a droid.

If I'm in a suit or an odd jacket, I do wear my jacket while sitting down. Reasons for it to come off would include eating messy indian food, making out with a lady, doing manual labor, going to the toilet, etc.
There is a middle ground though. Knitwear, especially a thin sweater with a V-neck can act as a vest over your shirt and tie, and thus spare you the need to wear a jacket. It might make you look like a prep school pupil, but that might actually be a cool look to pull off.

The answer to your quandary is the simplest thing imaginable: don't wear a tie.

 

I'd actually expand that with "wear jeans or informal chinos, an informal shirt like an oxford or a patterned summer shirt, and of course leave the collar unbuttoned".

 

If that is too informal for the workplace, then yes, I would wear a linen or seersucker jacket if it's too hot.