The string "0001F600" is the hexadecimal representation of a Unicode code point. As it is not in the BMP, you either need UTF32 or a UTF16 surrogate pair to represent it.

Here is some code to perform the requested conversion using UTF32 representation:

1. Parse as 32-bit integer:

   var utf32Char = uint.Parse("0001F600", NumberStyles.AllowHexSpecifier);

2. Convert this to a 4-element byte array in litte-endian byte order:

   var utf32Bytes = BitConverter.GetBytes(utf32Char);
   if (!BitConverter.IsLittleEndian)
       Array.Reverse(utf32Bytes);
   

3. Finally, use Encoding.UTF32 to make a string from it.

   var str = Encoding.UTF32.GetString(utf32Bytes);
   Console.WriteLine(str);
   

The string "1F600" is the hexadecimal representation of a Unicode code point. As it is not in the BMP, you either need UTF32 or a UTF16 surrogate pair to represent it.

Here is some code to perform the requested conversion using UTF32 representation:

1. Parse as 32-bit integer:

   var utf32Char = uint.Parse("1F600", NumberStyles.AllowHexSpecifier);

2. Convert this to a 4-element byte array in litte-endian byte order:

   var utf32Bytes = BitConverter.GetBytes(utf32Char);
   if (!BitConverter.IsLittleEndian)
       Array.Reverse(utf32Bytes);
   

3. Finally, use Encoding.UTF32 to make a string from it.

   var str = Encoding.UTF32.GetString(utf32Bytes);
   Console.WriteLine(str);