Design And Synthesis Of Activatable Organic Two-Photon Photosensitizer And Applications Research

Photodynamic therapy is a minimally invasive therapy based on photochemical reactions.It has non-invasiveness,highly selectively,low systemic toxicity,good targeting,repeated treatment,the fast healing process resulting in little or no scarring,and the lack of associated side effects compared to conventional therapies.Because of its advantages,it has been widely used in clinical medicine in recent years.However,excitation light penetration depth is shallow and a photo-toxicity on skin ultraviolet excitation are two major bottlenecks of the early photodynamic therapy?PDT?,which greatly limits the development and application of PDT in the field of biomedicine.Although the near-infrared excited PDT concept has been proposed in recent years,partly solved the problem of the penetration depth,but unfortunately,the photosensitizing process of the single-photon excitation not only produces cytotoxicity at the site of the lesion,but also produces unexpected cytotoxicity to the light-pathway tissues.Two-photon materials have a longer excitation wavelength?700-1000 nm?and a smaller excitation region near the focal point,so the two-photon photodynamic therapy has a deeper penetration depth and higher spatial resolution than the traditional single-photon photodynamic therapy.On the other hand,PDT of traditional photosensitizers has two major problems:non-specific localization and non-specific activation,non-specific localization may lead to unpredictable toxicity to normal tissues,while non-specific activation does not ensure photosensitizer aggregation in lesion tissues.Activatable photosensitizers are a special class of photosensitizers that are turned on by specific targeting molecules stimuli?microenvironments,enzymes,nucleic acids,etc.?,resulting in the production of singlet oxygen with strong cytotoxicity for targeted therapy,this has become a very active research direction in the field of photodynamic therapy.Although activatable photosensitizers for PDT have achieved significant progress in the last two or three decades,most of the materials obtained are single-photon excited,and there are few reports of two-photon excitation,which has seriously affected its In-depth application of bioimaging and biomedicine.Hence,this dissertation aims to design a class of reasonably activatable organic two-photon photosensitizers and expand its application in the field of photodynamic therapy.The research content of the dissertation includes the following three parts:?1?In this chapter,we designed and synthesized a nitric oxide?NO?activatable two-photon photosensitizer DBB-NO.The amidation reaction couples the NO-responsive group o-phenylenediamine?OPD?with the zwitterionic DBB,not only eliminating the possibility of dehydroascorbic acid and ascorbic acid interfering with fluorescence imaging,but also ensuring efficient photoinduced electron transfer?PeT?.The experimental results of the photophysical properties show that DBB-NO has an extinction coefficient(?=1.3×10⁵ M^-11 cm^-1)at 361 nm,which is two orders of magnitude higher than that of commercial two-photon materials,therefore DBB-NO has excellent light-absorbing ability.?2?In this chapter,the spectra and biological characterization of DBB-NO were carried out.Upon responding to NO,DBB-NO shows not only a remarkably enhanced fluorescence quantum yield??_F,0.17%vs 9.3%?and singlet oxygen quantum yield???,1.2%vs 82%?but also an extremely elevated TPA cross-section??,270 vs 2800 GM?.Simultaneous enhancement of??,?_F and?allows unprecedented two-photon fluorescence brightness??×?_F=260.4 GM?and two-photon PDT?TP-PDT?efficiency??×??=2296 GM?which precedes the value for commercial two-photon photosensitizer by two orders of magnitude.In addition,the photosensitizer has good chemical stability,low cytotoxicity,high selectivity toward NO,and the detection line of DBB-NO is 14 nM.Two-photon fluorescence imaging experiments show that DBB-NO can not only respond to NO to complete two-photon fluorescence imaging,but also has potential as a smart probe to distinguish activated macrophages from normal ones.Two-photon photodynamic therapy experiments have shown that DBB-NO can not only be activated by endogenous NO,but also produce phototoxic effects on inflammatory tissues,and it can be served as a smart theranostic agent to selectively destroy activated macrophage from normal ones for a precision therapy.?3?In this chapter,we designed and synthesized two two-photon photosensitizers BAB and DBB with the same host conjugated backbone and different side chains.Through the host-guest complexation,water-soluble pillar[5]arene?WP5?was combined with the two photosensitizer side chain quaternary ammonium group,this can almost completely block its intersystem crossing?ISC?to inhibit the generation of singlet oxygen.Before host-guest complexation,the singlet oxygen quantum yields????of BAB,and DBB were 51%,and 89%respectively,and after host-guest complexation,the??of WP5???BAB,and WP5???DBB were 21%and 5.7%respectively.Due to the special responsiveness of WP5 to acidic pH,WP5???DBB has the potential to act as an excellent pH-activatable two-photon photosensitizer,constructing a pH-activatable two-photon photodynamic therapy system.