Femtosecond intersystem crossing to the reactive triplet state of the 2,6-dithiopurine skin cancer photosensitizer

Abstract

This study elucidates the electronic relaxation mechanism leading to the population of the reactive triplet state in 2,6-dithiopurine; the most effective dithionated nucleobase skin cancer photosensitizer agent reported thus far.

Ultrafast Intersystem Crossing in Selenium-Annulated Perylene Bisimide

“…62 Highly reactive and prevalent singlet oxygen finds application in photodynamic therapeutic purposes since it kills the tumorous or diseased cells. 47,63 During the singlet oxygen quantification analysis, the triplet excitation energy of Se-PBI ( 3 *Se-PBI; photosensitizer) is transferred to ground-state (triplet) oxygen ( 3 Σ g ), resulting in singlet oxygen ( 1 Δ g ) generation. The singlet oxygen quantum yield, = 73.8% for Se-PBI, is one of the remarkable values reported among the modified PBI derivatives (Table S2 and Figure S13).…”

Thieno[3,4-d]pyrimidin-4(3H)-thione: an effective, oxygenation independent, heavy-atom-free photosensitizer for cancer cells

“…100 μm) than 2,6-dithiopurine, one of the most promising thiobase PDT agents reported to date. 42,48…”

“…100 mm) than 2,6-dithiopurine, one of the most promising thiobase PDT agents reported to date. 42,48 The emission spectra of ThiaHX in phosphate buffer (pH 7.4) and in MeCN are presented in Fig. S1.…”

“…We note that the lifetime associated with the intersystem crossing event is longer than the lifetimes measured for this process in the thiobases and other thionated derivatives, which occur in a sub-picosecond timescale. 13,18,44,48,[54][55][56][57][58][59] We proposed that the reason for the slower intersystem crossing is largely due to the weaker spin-orbit coupling (SOC = 83 cm −1 , relative to thiobases and other thionated compounds) calculated between the states involved in the intersystem crossing pathways and the energy barrier that must be overcome to access the crossing region. Typically, the SOCs for thiobases and other thionated derivatives are >100 cm −1 .…”

“…Typically, the SOCs for thiobases and other thionated derivatives are >100 cm −1 . 18,48,57,59 Photodynamic efficacy of ThiathioHX against monolayer cancer cells Conventional PDT requires the employment of a photosensitizer that upon photoactivation, populates the reactive triplet state and generates ROS such as singlet oxygen, hydroxyl radical, hydrogen peroxide and super oxide anion, through Type I and/or Type II photosensitization mechanisms. 60 These ROS can damage intracellular lipids, proteins and nucleic acids to ultimately cause cell death.…”