conversion failed when converting date and or time from character string

i want to search record with dropdown list and text box 

i have fields in dropdown like 

1.Orthopedics

2.Clinic

3.Pharmacy

4.ENT

when i select one field and type date in text box i want a list of record submitted on this date with the specific field 

I Tried This 

protected void Button1_Click(object sender, EventArgs e)
        {

        
            DateTime date1 = Convert.ToDateTime(TextBox1.Text);
            con.Open();
            SqlCommand cmd = new SqlCommand("SELECT * FROM KSMCemp_data WHERE Exp_Date='" + date1 + "'",con);
         
           
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            GridView1.DataSource = ds;
            GridView1.DataBind();
          

          
        }

Giving this error 

conversion failed when converting date and/or time from character string