private void richTextBoxSend_KeyPress(object sender, KeyPressEventArgs e)
{
    if (e.KeyChar == (char)Keys.Enter)
    {
    }
    else if (e.KeyChar == (char)Keys.F1)
    {        
    }
    else if (e.KeyChar == (char)Keys.F2)
    {
    }
}

private void richTextBoxSend_KeyDown(object sender, KeyEventArgs e)
{
      if (e.KeyData == Keys.F1)
      {
      }
      else if (e.KeyData == Keys.F2)
      {
      }
}