Table 2.

Ideal properties of a photosensitizer (PS) for photodynamic therapy (PDT).

Property	Description	References
Easy synthesis	Optimizing PS synthesis is crucial for high yields and purity, affecting production scale and cost.	[3,113]
Absorption in the visible and near-infrared regions	Low-energy radiation reduces harm to healthy tissues and increases light permeability in biological tissues for deeper activation of PS.
Amphiphilicity	Amphiphilic compounds are water-soluble and can easily cross the lipid membranes of cells, ensuring their availability and distribution, allowing the PS to target and accumulate in abnormal tissues more efficiently.	[123]
Various routes of administration	The PS or its formulation must allow safe and painless administration, whether performed orally, topically, or intravenously. In addition, several administration routes will enable the use of the same molecule in a broader range of diseases.	[124]
Selective tumor accumulation	It should be able to reach the neoplasia in a short time as well as selectively accumulate in tumor cells.	[125]
Harmless in the absence of light	Molecules that intrinsically have cytotoxicity should not be studied as potential PSs. To be applied in PDT, photosensitizing candidates must exhibit zero to low toxicity in the dark and significant cytotoxicity only when irradiated.	[123,126]
Resistance to photobleaching	The term “photobleaching” refers to the loss of the ability of the PS to absorb light due to its degradation during irradiation. Resistance to this phenomenon allows the use of higher energy light sources, which may result in deeper tissue penetration and greater therapeutic efficacy.	[127,128]
Long-term triplet state lifetime	The triplet state PS reacts with triplet molecular oxygen to produce ROS for type I and II PSs. Long-term triplet state lifetime enables a prolonged generation of cytotoxic species, which is crucial for the death of target cells.	[129]
Rapid clearance from the body	A rapidly cleared PS from the organism significantly decreases the duration of its presence in the body, thereby minimizing the risk of toxicity to healthy tissue and reducing the risk of side effects such as skin photosensitivity.	[126]