Carbazole-based molecular units are ubiquitous in organic optoelectronic materials; however, the excited-state relaxation of these compounds is still underexplored. Here, we provide a detailed investigation of carbazole (Cz) and 3,6-di-
tert-butylcarbazole (
t-Bu-Cz) in organic solvents using femtosecond and nanosecond UV–Vis–NIR
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Carbazole-based molecular units are ubiquitous in organic optoelectronic materials; however, the excited-state relaxation of these compounds is still underexplored. Here, we provide a detailed investigation of carbazole (Cz) and 3,6-di-
tert-butylcarbazole (
t-Bu-Cz) in organic solvents using femtosecond and nanosecond UV–Vis–NIR transient absorption spectroscopy, as well as time-resolved fluorescence experiments upon photoexcitation in the deep-UV range. The initially prepared S
x singlet state has a (sub-)picosecond lifetime and decays to the S
1 state by internal conversion (IC). The S
1 state exhibits absorption peaks at 350, 600 and 1100 nm and has a lifetime of 13–15 ns, which is weakly dependent on the solvent. Energy transfer from vibrationally hot S
1 molecules (S
1*) to the surrounding solvent molecules takes place with a time constant of 8–20 ps. The T
1 triplet state is populated by intersystem crossing (ISC) from S
1 with a typical quantum yield of 51–56% and shows a lifetime which is typically in the few microseconds regime. The S
1 and T
1 states of both carbazole compounds in solution are strongly quenched by O
2. Two-photon excitation leads to the formation of a small amount of the respective radical cation. The influence of the
tert-butyl substituents on the photophysics is relatively weak and mainly reflects itself in a small increase in the Stokes shift. The results provide important photophysical information for the interpretation of carbazole relaxation in more complex environments.
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