Mushrooms such as the dermocyboid Cortinarius rubrophyllus are characterized by strikingly colorful fruiting bodies. The molecular dyes responsible for such colors recently experienced a comeback as photoactive compounds with remarkable photophysical and photobiological properties. One of them—7,7′-biphyscion—is a dimeric anthraquinone that showed promising anticancer effects in the low nanomolar range under blue-light irradiation. Compared to acidic anthraquinones, 7,7′-biphyscion was more efficiently taken up by cells and induced apoptosis after photoactivation. However, seasonal collection of mushrooms producing this compound, low extraction yields, and tricky fungal identification hamper further developments to the clinics. To bypass these limitations, we demonstrate here an alternative approach utilizing a precursor of 7,7′-biphyscion, i.e., the pre-anthraquinone flavomannin-6,6′-dimethyl ether, which is abundant in many species of the subgenus Dermocybe. Controlled oxidation of the crude extract significantly increased the yield of 7,7′-biphyscion by 100%, which eased the isolation process. We also present the mycochemical and photobiological characterization of the yet chemically undescribed species, i.e. C. rubrophyllus. In total, eight pigments (1–8) were isolated, including two new glycosylated anthraquinones (1 and 2). Light-dependent generation of singlet oxygen was detected for the first time for emodin-1-O-β-d-glucopyranoside (3) [photophysical measurement: Φ∆ = 0.11 (CD3OD)]. Furthermore, emodin (7) was characterized as promising compound in the photocytotoxicity assay with EC50-values in the low micromolar range under irradiation against cells of the cancer cell lines AGS, A549, and T24. Graphical abstract