at d8 this spell seems to basically make Shocking Grasp irrelevant.

Thank you for your feedback!

I wouldn't say irrelevant. I think Shocking Grasp still has its place. It prevents the target from taking reactions until the start of its next turn, in addition to granting advantage against targets wearing metal—while a niche feature, perhaps, it comes in handy when your wizard finds themselves face to face with an armored soldier. It doesn't require a weapon either.

This cantrip is based off of Booming Blade, but with an inverted conditional. They fulfill different roles. Booming Blade incentivizes a creature to stick to the caster; a dangerous place for a caster to be. Charged Blade, on the other hand, incentivizes a creature to back out of the caster's reach (yes, possibly drawing an Attack of Opportunity, but casters will likely want their reactions for more important things, imo). This, in turn, might give the caster a chance to put more distance between themselves and danger on the subsequent turn.

Just like other cantrips, you could definitely build around it, finding synergies, like coupling this and Booming Blade with Warcaster. Hit them with Lightning, and then, if they run, Thunder. And that's fun and thematic!

I loved the Design, Will definitely allow this for my players. But I Would reduce the post effect damage to d6's instead.

Why:
Comparing it to booming blade, booming blade punishes your enemy for running away from you. But after the damage the enemy is "safe".
Charged blade, on the other hand, punishes the enemy to keep engagement with you. So it is a really powerful tool for two cases:
-If you are a squish caster and want enemies to stay away
-If you are a DPS focused arcane fighter and want to increase DPS by either forcing an opportunity attack or the damage itself.

On the first case, it is still a little bit stronger then booming blade.
But on the second case, it is just OP.
Both options your enemy have are bad, either taking 1-4d8 damage guarantee or an opportunity attack.

I will reduce the damage to 1d6 and remove the "no reaction" debuff for this spell to use it in my campaigns.

The intent might be for squishies to encourage disengage but any melee character could take magic initiate to learn this and it’s just broken. On a bladesinger wizard it’s already broken—no feat cost even associated. Add sentinel and now you have almost guaranteed extra damage if the enemy tries to flee because now they CAN’T leave the range of the spell. 
i love the intent of this spell and the mirrored effect of booming blade, but as written, with the high guaranteed massive damage boost AND removal of reactions this is just so OP.

Within the spell's range? It should probably just say "within 5 feet of you" to be clearer.

And I agree with others: Take off the losing reactions since it already does as much damage as shocking grasp.

I understand the intent is to motivate a creature to back away from a caster as the inverse to booming blade, however this fails to remain balanced due to the disengage mechanics of the game. As others have already pointed out, forcing an opponent creature to choose between taking an opportunity attack, taking spell damage or burning an action to disengage is waaay too strong for a cantrip. Booming Blade is balanced in the sense that the targeted creature has just two very simple options of taking damage if it needs to move or just standing still and hitting whatever is in range. In essence it's both a kiting mechanic and a taunt-like mechanic. To achieve the desired effect of giving a caster some wiggle room, it may be better to tie the damage to the target creatures attacks. I've written a variant below which I feel is far more suitable to what you're trying to achieve without breaking the combat mechanics:

You brandish the weapon used in the spell’s casting and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and then becomes positively charged with electrostatic magic until the start of your next turn. If the target makes a melee attack against you before then, the target takes 1d8 lightning damage, and it can't take reactions until the start of its next turn.

This spell’s damage increases when you reach certain levels. At 5th level, the melee attack deals an extra 1d8 lightning damage to the target on a hit, and the damage the target takes for making a melee attack against you increases to 2d8. Both damage rolls increase by 1d8 at 11th level (2d8 and 3d8) and again at 17th level (3d8 and 4d8).

Why this works... a martial class will have extra attack which will be far more beneficial then casting a spell which only allows for one attack. Also unlike shocking grasp which uses the spell attack bonus, this uses either STR or DEX to hit (honourable mentions to Artificer and Hexblade I know). This also means the targeted creature still has the option of using their action to attack something else or even risking an opportunity attack to get in range of attacking something else. Ideally in the latter instance it's taking an opportunity attack from a spellcaster so it won't be as big a threat as a martial class. If it's up close and personal with a martial class that used this, well it's still not taking as much damage as it would have from 2 attacks in the initial attack, and there's always the chance it can use the help action for an allied creature within 5ft to attack the caster too.

should be on the artificer's spell list as well, since both this one's sister spells are also on the artificer list.

I agree with JeanLow (use d6s) and Lycaon (artificer list).  I definitely hear what robrhema is saying too -- this seems like a must-have.  Making people move away from a caster is awesome.  Look at all the other movement cantrips - lightning lure, for example, or thorn whip - they all move creatures closer to the caster, but do nice damage.  Feels like the ability to push and do nice damage might be too much.

Think about being a bladesinger 6 fighter 2 making your 2 attacks with charged bladed and a normal attack, then action surge and make 2 more attacks with booming blade and 1 normal attack. does someone else hear the song "should i stay or should i go now?" XD

Yes but this would also remove any melee characters multi attack which would balance it out. Also the same can be said for the booming blade which is literally the same

Not true for a bladesinger. When they get extra attack at level 6 they also can replace one attack with a cantrip. Eldritch knight gets effectively the same at level 7. 

yea but that is an exception u dont balance things around 1 or 2 things unless its ment to be used only by them

Think about a bladesinger 6 fighter 2 making two attacks, one with booming blade and one normal. Then action surge, make one attack and cast conjure bonfire under the target's feet.

Yes, if a level 8 PC uses a once-per-short rest ability they can do some powerful things. The "problem" you're identifying there is action surge, which isn't really even a problem.

I play it as the same square that they were attacked (since that is how i intrepreted it). So my creatures just move to the left or the right without provoking AOO and avoid the damage. And it works well in Hallways where is shines or when a creature is stuck somehow. In that sense it's not too strong is it?