datetimepicke convert problem

private void button4_Click(object sender, EventArgs e)
       {
 
           Convert.ToDateTime(this.dateTimePicker1.Value).ToString("MM/dd/YYYY");
           textBox1.Text = dateTimePicker1.Text;
       }
 
       private void button1_Click(object sender, EventArgs e)
       {
           try
           {
              
               con.Open();
                   
               String q = "insert into Development_Detal values('" + Ename.Text + "','" + UserPass.Text + "','" + EmpID.Text + "','" + address.Text + "','" + emaill.Text + "','" +textBox1.Text+"','" + mobNo.Text + "','" + city.Text + "' )";
 
               SqlCommand cmd = new SqlCommand(q, con);
              
 
               if ((Ename.Text == "") || (UserPass.Text == "") || (EmpID.Text == "") || (address.Text == "") || (mobNo.Text == "") || (city.Text == ""))
               {
                   MessageBox.Show("Must be fill all data ");
               }
               else
               {
                   cmd.ExecuteNonQuery();
                   MessageBox.Show("Employee Registration Successfully");
               }
           }
 
               catch(Exception ex)
               {
                   MessageBox.Show(ex.Message);
               }
           finally
           {
               con.Close();
           }
 

         }