The
photochemistry and photophysics of thiocarbonyl compounds,
analogues of carbonyl compounds with sulfur, have long been overshadowed
by their counterparts. However, recent interest in visible light reactions
has reignited attention toward these compounds due to their unique
excited-state properties. This study delves into the ultrafast dynamics
of 7-diethylaminothiocoumarin (TC1), a close analogue of the well-known
probe molecule coumarin 1 (C1), to estimate intersystem crossing rates,
understand the mechanisms of fluorescence and phosphorescence, and
evaluate TC1’s potential as a solvation dynamics probe. Enclosing
TC1 within an organic capsule indicates its potential applications,
even in aqueous environments. Ultrafast studies reveal a dominant
subpicosecond intersystem crossing process, indicating the importance
of upper excited singlet and triplet states in the molecule’s
photochemistry. The distinct fluorescence and phosphorescence origins,
along with the presence of closely spaced singlet excited states,
support the observed efficient intersystem crossing. The sulfur atom
alters the excited-state behavior, shedding light on reactive triplet
states and paving the way for further investigations.