The absorption maxima of compounds 4a-d are located around 450-460 nm, similar to the parent compound 2, except for 4c, which shows a deviation. The absorption maxima vary significantly among derivatives 3a-d: 3a absorbs at 457 nm, 3b and 3d at about 490 nm, while 3cat 518 nm. This difference can be attributed to the lack of conjugation between the acceptor group and the perylene core in substances 4a to 4d that arises from the antiperiplanar arrangement of perylene and the thiophene linker. Conversely, in compounds 3a-3d, the perylene core is conjugated with both the double bond and the acceptor group, significantly influencing the photophysical properties of these molecules. The quantum yield of singlet oxygen (ΦΔ) was measured for all synthesized compounds. Riboflavin was chosen as the standard due to its absorption spectrum partially overlapping with those of the investigated substances. Since literature data for the quantum yield of singlet oxygen generation by riboflavin in methylene chloride were unavailable, we calculated ΦΔ using riboflavin in methanol as the reference standard. Compounds 3a-3d exhibited very low siglet oxygen generation (ΦΔ ~0.01), while compounds 4a-d demonstrated a significantly higher capacity for singlet oxygen generation (Figure ). This difference can be attributed to the presence of the thiophene fragment in 4a-d, which strongly enhances the ROSgenerating ability of the perylene core .