The ultrafast relaxation of jet-cooled aniline was followed by time-resolved ionization, after excitation in the 294-234 interval. The studied range of energy covers the absorption of the two bright ππ∗ excitations, S(1) and S(3), and the almost dark S(2) (πσ∗) state. The employed probe wavelengths permit to identify different ultrafast time constants related with the coupling of the involved electronic surfaces. A τ(1) = 165 ± 30 fs lifetime is attributed to dynamics along the S(2) (πσ∗) repulsive surface. Other relaxation channels as the S(1)→S(0) and S(3)→S(1) internal conversion are also identified and characterized. The work provides a general view of the photophysics of aniline, particularly regarding the role of the πσ∗ state. This state appears as minor dissipation process due to the ineffective coupling with the bright S(1) and S(3) states, being the S(1)→S(0) internal conversion the main non-radiative process in the full studied energy range. Additionally, the influence of the off-resonance adiabatic excitation of higher energy electronic states, particularly S(3), is also observed and discussed.

The photoprotective capabilities of a family of synthetic MAA analogues have been investigated.

The evolution of the isolated pyrrole molecule has been followed after excitation in the 265-217 nm range by using femtosecond time delayed ionization. The transients collected in the whole excitation range show the vanishing of the ionization signal in the femtosecond time scale, caused by the relaxation along a πσ(∗) type state (3s a(1)←π 1a(2)), which is the lowest excited electronic state of the molecule. This surface is dissociative along the NH bond, yielding a 15 ± 3 fs lifetime that reflects the loss of the ionization cross-section induced by the ultrafast wavepacket motion. Although a weak πσ(∗) absorption is detected, the state is mainly reached through internal conversion of the higher bright ππ(∗) transitions, which occurs with a 19 ± 3 fs lifetime. In addition to its resonant excitation, the intense ππ(∗) absorption extending in the 220-190 nm interval is also out-of-resonance populated at energies far to the red from its absorption onset. This coherent adiabatic excitation of the ππ(∗) transition should follow the excitation pulse (coherent population return effect), but instead the system relaxes toward the lower πσ(∗) surface through a conical intersection during the interaction time, leading to the population of πσ(∗) state at wavelengths as long as 265 nm. According to the observed behavior, the time evolution of the system in the full excitation range studied is modeled by a coherent treatment that provides key insights on the photophysical properties of the molecule.

The photodynamics of an orthogonal BODIPY dimer, particularly the formation of triplet states, has been explored by femtosecond and nanosecond transient absorption measurements. The short time scale data show the appearance of transient features of triplet character that, according to quantitative analysis of their intensities, account for more than 100% of the initially excited molecules, which reveals the occurrence of a singlet fission process in the isolated dimers. The formation rate of the triplet correlated state (TT) is found to depend on the solvent polarity, pointing to the mediation of a charge transfer character state. The dissociation of the(TT) state into pairs of individual triplets determines the triplet yield measured in the long time scales. The kinetic model derived from the results provides a comprehensive view of the photodynamics of BODIPY dimers and permits rationalization of the photophysical parameters of these systems.

The relaxation dynamics of the isolated indole molecule has been tracked by femtosecond time-resolved ionization. The excitation region explored (283-243 nm) covers three excited states: the two ππ* L(b) and L(a) states, and the dark πσ* state with dissociative character. In the low energy region (λ > 273 nm) the transients collected reflect the absorption of the long living L(b) state. The L(a) state is met 1000-1500 cm(-1) above the L(b) origin, giving rise to an ultrafast lifetime of 40 fs caused by the internal conversion to the lower L(b) minimum through a conical intersection. An additional ~400 fs component, found at excitation wavelengths shorter than 263 nm, is ascribed to dynamics along the πσ* state, which is likely populated through coupling to the photoexcited L(a) state. The study provides a general view of the indole photophysics, which is driven by the interplay between these three excited surfaces and the ground state.