Add folder exclusion for windows defender using powershell through C#

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C#4.0

Hello everyone,
I am trying to add Folder Exclusion for Windows Defender using PowerShell through C#
This only works if the path is short, for example:
"C:\New folder"
If the path is a bit longer it doesn't work, for example:
"C:\New folder\New folder1"
What's the problem? Can someone help me please. Thank you.
Below is my code which works fine only if the folder path is short.

What I have tried:

private void addFolderToExclusion()
         {
             try
             {
                FolderBrowserDialog fbd = new FolderBrowserDialog();
                if (fbd.ShowDialog() == System.Windows.Forms.DialogResult.OK)              
                string path = openFileDialog1.FileName;
                startInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
                startInfo.FileName = "powershell.exe";
                startInfo.Arguments = "-command \"Add-MpPreference -ExclusionPath " + path + "\"";
                process.StartInfo = startInfo;
                process.Start();
                process.WaitForExit();
             }
             catch
             {    
             }
         }