Thanks for responding.
How do you know there is really photochemistry happening? Color change? TLC? NMR evidence?
I have checked HPLC after photolyzing the compound and performed mass spectrometry (with the control sample, i.e. no light) to show that the compound is no longer the intact parent molecule. Also, the compound also changed color after photolysis.
Depending on the ionization method, even perfectly stable compounds undergo fragmentation during mass spectral analysis. Hopefully observing the fragments isn't your only indication that you think your compound is decomposing.
The control (without light) under the same ionizing condition did not give the same fragmentation pattern. The intact molecule is still present 100%.
2- and 4-nitrobenzyl ethers and esters do undergo cleavage by light, eliminating the alkoxide or carboxylate. Maybe your reaction is related.
I will have to check this out.