Catching ultrafast photo-processes in the act: the virtual time-resolved spectrometer

Recent advances in theoretical models enable the use of computational tools as a virtual ultrafast spectrometer1, allowing to simultaneously disentangle ultrafast photo-processes and deliver their underlying time-resolved spectroscopies. The theoretical characterization of unraveled photoinduced molecular dynamics opens the door to potential directions of developments, driving experiments vs future unexpected employments and applications. This computational approach has been systematically validated on different chromophores (see Figure 1) and in different environments (native, in solution or in vacuum). An example of a study that is revealing unexpected properties with interesting potential application are thiobases2, sulfur-substituted nucleobases analogs, exhibiting completely different photophysical properties than canonical bases. As they are characterized by high quantum yield of triplet population through intersystem crossing processes, they have long been considered crucial in biomedical applications, particularly in photodynamic therapies. By combining time-resolved photoelectron spectroscopy and theoretical quantum chemistry models, doubly thionated 2,4-dithioUracil revealed unpredicted multiple decay processes that dependent on excitation energies. Surprisingly, such different pathways traced the distinctive behavior of singly substituted 2- or 4-thioUracil by simply shifting the pump pulse through the UV-A and UV-B windows. The double thionated base thus becomes a system/instrument whose lifetime and rates of triplet formation become properties that can be easily tuned and controlled, offering unpredictable developments for the field of organic light-emitting diodes (OLEDs), which are emerging in an increasing number of applications.