**2. Photodynamic therapy**

Tetrapyrrolic pigments with porphyrinoid origin are frequently used as photosensitizing agents in PDT [3]. The reactive oxygen species (ROS) required for the photodynamic effect can be produced efficiently by these porphyrinoid systems. Apart from that, these porphyrin-based systems exhibit fluorescence. The fluorescent photosensitizers with cancer-targeting properties can be used to perform cancer diagnosis and fluorescence-guided surgery with fluorescence imaging techniques. Porphyrinoids can form strong coordination complexes with a variety of metals including gadolinium. This approach can be effectively utilized for developing porphyrin-based magnetic resonance imaging (MRI) contrasting agents for MRI imaging as a diagnostic tool. The current treatment modalities change more toward theranostic approaches. These multifunctional substances have both medicinal and diagnostic capabilities in a single molecule and are the major focus of the current research [10, 11]. Theranostic will be heavily used in future tailored therapies and medication delivery. It could be called "P4 medications," or in other words, preventive, personalized, participatory, and predictive medicine [12, 13]. In addition to fluorescence-guided imaging, other diagnostic techniques, such as magnetic resonance imaging and photoacoustic imaging, can be tried depending on the PS when constructing PDT [14, 15]. One of the most difficult challenges in the molecular design of PS for PDT is the ability to selectively target a specific sick tissue or organ. Different carrier techniques or formulation approaches can be tested to improve cancer targeting to provide a selectively focused effect [16, 17]. Various methods, such as carbon nanodots, pH- and temperature-sensitive nanoparticles, and liposomes, have been developed to deliver medications deeply into tumors [18, 19]. Apart from cancer, PDT has greater acceptance in the treatment of conditions, such as acne vulgaris alopecia, and vitiligo [20, 21]. As a result, PDT is a viable therapeutic approach with all of its benefits.
