Phyton - Lookup of a data in another sheet and copy to a new file if not found

I am new to programming and I am trying to learn. I am comparing 2 documents that have very similar data. I want to find out if data from column "concatenate" is found in the same column "contatenate" from the other document because I want to find out what changes where made during the last update of the file.
If the value cannot be found this whole row should be copied to a new document. Then I know that this dataset has been changed.

Here is the code I have:

import pandas as pd

# load the data from the two files into Pandas dataframes
df1 = pd.read_excel('/Users/bjoern/Desktop/PythonProjects/Comparison/MergedKeepa_2023-02-05.xlsx')
df2 = pd.read_excel('/Users/bjoern/Desktop/PythonProjects/Comparison/MergedKeepa_2023-02-04.xlsx')

# extract the values from column Concatenate in both dataframes
col_a_df1 = df1['concatenate']
col_a_df2 = df2['concatenate']

# find the intersection of the values in column A of both dataframes
intersection = col_a_df1.isin(col_a_df2)

# filter the rows of df1 where the value in column A is not found in df2
df1 = df1[intersection]

# write the filtered data to a new Excel file
df1.to_excel('/Users/bjoern/Desktop/PythonProjects/Comparison/filtered_data.xlsx', index=False)

I just duplicated the 2 inputfiles which means I should receive a blank document but the document is still copying data to the new sheet.

What did I do wrong?

Many thanks for your support!

> If the value cannot be found, this whole row should be copied to a new
> document.

IIUC, you need (~), the NOT operator, to negate your boolean mask :

df1 = df1[~intersection]