Ultrafast electronic and vibrational dynamics in brominated aluminum corroles: Energy relaxation and triplet formation

Abstract

We combined femtosecond (fs) VIS pump–IR probe spectroscopy with fs VIS pump–supercontinuum probe spectroscopy to characterize the photoreaction of the hexacoordinated Al(tpfc-Br8)(py)2 in a comprehensive way. Upon fs excitation at ∼400 nm in the Soret band, the excitation energy relaxes with a time constant of (250 ± 80) fs to the S2 and S1 electronic excited states. This is evident from the rise time of the stimulated emission signal in the visible spectral range. On the same time scale, narrowing of broad infrared signals in the C=C stretching region around 1500 cm−1 is observed. Energy redistribution processes are visible in the vibrational and electronic dynamics with time constants between ∼2 ps and ∼20 ps. Triplet formation is detected with a time constant of (95 ± 3) ps. This is tracked by the complete loss of stimulated emission. Electronic transition of the emerging triplet absorption band overlaps considerably with the singlet excited state absorption. In contrast, two well separated vibrational marker bands for triplet formation were identified at 1477 cm−1 and at 1508 cm−1. These marker bands allow a precise identification of triplet dynamics in corrole systems.

The First Silicon(IV) Corrole Complexes: Synthesis, Structures, Properties, and Formation of a μ‐Oxo Dimer

“…In contrast, the decay of the TA spectra of 3 a at λ probe =610 nm was fitted with triple exponential decay components of τ 1 =2.2 ps (8 %), τ 2 =23 ps (11 %), τ 3 =7.2 ns (71 %), and a constant residual (10 %) in the ESA domain (Figures S8‐2 c and d in the Supporting Information). The very fast decaying and rising components in a picosecond time domain observed for both 2 a and 3 a ( τ 1 =1 and 2.2 ps, respectively) have been considered to correspond to the vibrational relaxation process in the singlet excited states, as previously reported in the case of brominated aluminum corroles . The fast rising component with τ 2 =23 ps observed in 3 a has been attributed to a structural relaxation to the S 1 state and thus, components with τ 2 =4.8 ns for 2 a and τ 3 =7.2 ns for 3 a have been assigned to decays of conformationally relaxed S 1 states of 2 a and 3 a to give their triplet states with long lifetimes (the observed constant residuals) and the ground states.…”

Influence of Heterogeneity on the Ultrafast Photoisomerization Dynamics of Pfr in Cph1 Phytochrome

“…The major component showed a Lumi‐F photoproduct generation with a time constant of 1.5 ps and a hot ground‐state generation with decay constants of 770 fs and 2.8 ps . Because electronic state dynamics of phytochromes are spectrally complex, we analyzed the system by combining electronic state dynamics measured by femtosecond (fs) visible (Vis) pump–supercontinuum Vis probe spectroscopy with angle‐balanced polarization‐resolved femtosecond Vis pump–infrared (IR) probe spectroscopy . This allows us to separate electronic dynamics from photoproduct generation and hot ground‐state relaxation .…”

Photophysical Heavy-Atom Effect in Iodinated Metallocorroles: Spin–Orbit Coupling and Density of States

“…Indeed, a near-unity triplet yield was determined by time-resolved IR spectroscopy for Br 8 -Al. 45 Ge(TTC)(OH) 9.98×10 8 1000 ref. 48 a k nr 0 + k ISC value determined in pyridine; 5 b k nr 0 + k ISC value determined in benzene; 5 c Triplet formation occurs with a low quantum yield.…”

“…Typically, these triplet states live hundreds of microseconds 7,9,47 and undergo efficient energy-transfer quenching by oxygen. For free-base corroles, the ISC rate depends on the extent of fluorination of the meso-phenyl groups, 8 increases upon β-bromination of the pyrrol rings, 39,45 introducing a Cl or I atom on one of the meso-phenyls, 33,41 or upon complexation with main-group elements Ga III and Al III , 42 as well as P V and Ge IV . 48 The (near) absence of fluorescence in emission spectra of phosphorescent Ir III and Au III complexes point to a very fast ISC, although its rate has not been reported.…”