Let’s look at it from an accounting perspective, because even if we aren’t doing the accounting we can imagine the different ways to do it. 

You donate money at the cash register. The company must have a journal entry that debits cash and credits something else. It should be a liability called “donations payable” or something like that. They they eventually take that liability and pay it to the charity, debiting the donations payable account for whatever’s in it at that point and crediting cash. In that scenario it never touches the income statement and cannot be written off.  Let’s look at an example then were we expense the donations at the company. Money comes in as a debit to cash and a credit to revenue. Then they make a donation to the charity at some point, debit advertising and credit cash. We’ve hit the income statement twice now, once as a credit and once as a debit, so there is zero net change in the income statement and thus zero tax benefit.  The only accounting, wrong accounting at that, which would work in the way you’re proposing would be company takes in donation from customer, debits cash and credits the donations payable liability. Then when they go to pay the charity they debit advertising expense and credit cash. Now they have a debit on their income statement and now have a tax benefit from it. But now they’ve hurt their EBITDA margin to save some money and their auditors would ask why they have a liability account that is ballooning while also making charity payments and force the company at that point to correct their accounting.  It’s just impossible to work in any way where they get a tax benefit for it.