Time-resolved spectroscopic studies of psoralens, khellin, visnagin and lumichrome and derivatives

Psoralens, coumarins and flavins are biologically active photosensitizers, which have been used in pathogen inactivation of blood products, cancer treatment and skin diseases. Laser flash photolysis (LFP) with UV-visible and infrared detection and Density Functional Theory (DFT) calculations were used to directly observe and identify the triplet states of psoralens, coumarins and lumichromes, and their intermediate derivatives, and to understand their chemical reactivity. The triplet-excited states of the parent psoralen as well as 8-methoxypsoralen, 5-methoxypsoralen and trimethylpsoralen were directly observed in acetonitrile using UV-visible or time-resolved infrared (TRIR) spectroscopy. TRIR spectra of trimethylpsoralen radical ions were also obtained. These experimental observations were supported by computational studies.; The vibrational spectra of triplet visnagin and khellin, and their radical cations and anions were obtained upon 266 nm LFP in acetonitrile. Visnagin and khellin triplet excited states react with chloranil to form their radical cations and the chloranil radical anion. The radical cation of khellin and visnagin both present a vibrational band at 1136 cm-1. The excited states of khellin, visnagin and chloranil are all involved in the light induced electron transfer reaction. Khellin and visnagin triplets both react with anionic electron donors (NaI or KSCN) to form the related radical anions. Triplet visnagin reacts with hydroquinone to form semiquinone radicals. The vibrational band at 1225 cm-1 of the visnagin derived radical was assigned to a C-H rocking mode on the basis of DFT calculations.; In the exploratory photochemistry of lumichrome and its oxides, both nanosecond and ultrafast laser flash photolysis with UV-visible and TRIR spectroscopy were used to observe the transient species generated photochemically from lumichrome (LC), lumichrome-N-oxide (LCO) and lumichrome-di-N-oxide (LCO 2) and the data were interpreted with the aid of DFT calculations. The transient absorption spectra and the lifetimes of the triplet states of lumichrome, lumichrome N-oxide and lumichrome di-N-oxide were measured by LFP methods with UV-vis detection and TRIR spectroscopy upon 266 nm LFP in acetonitrile. The transient UV-vis spectra of 3LC*, 3 LCO* and 3LCO2* were obtained upon 266 nm LFP in argon saturated acetonitrile and their lifetimes were determined to be about 1 mus in deoxygenated acetonitrile. The transient vibrational spectra of LC, LCO and LCO2 triplet excited states were obtained upon 266 nm and present similar features with strong IR bands assigned to the carbonyl C=O and C=N stretching vibrations as predicted by the DFT calculations. The singlet states of lumichrome, lumichrome-N-oxide, lumichrome-di-N-oxide, isoquinoline N-oxide and pyridine N-oxide were identified by picosecond time-resolved absorption spectroscopy. Time-correlated single photon counting (TCSPC) and fluorescence spectroscopy were used to determine the lifetimes of the singlet states and fluorescence quantum yields of these aromatic N-oxides as well as isoquinoline N-oxide (IQNO), pyridine N-oxide (PNO), riboflavin tetraacetate and riboflavin tetrabenzoate.