Yes, if you intend to sponsor a Public Service Announcement Campaign, this business expense would be considered a promotion or advertising expense. The entire expense would be deductible.
The tax deductible donation is not treated in a similar fashion for in an S corporation, as in this case the donation is a K-1 item and would be reported as a distributable item on the individual shareholders K-1!
For a C corporation, the tax deductible donation is also treated differently and in this case, the IRS rules state the the Corporation is entitled to deduct upto a maximum of 10% of a Corporations net taxable income without consideration of NOL and Charitable contribution. In other words, calculate the taxable income w/o deduction of charitable contribution, and a maximum limit is 10% of this taxable income.
Therefore, if there is no taxable income, the corporations would not be able to deduct charitable contributions for that calendar year.