We report the results of an extended time-resolved study of DNA nucleobases in aqueous solutions conducted in the deep UV using broadband femtosecond transient absorption and electronic two-dimensional spectroscopies. We found that the photodeactivation in all DNA nucleobases occurs in two steps -fast relaxation (500-700 fs) from the excited state ππ* to a "dark" state, and its depopulation to the ground state within 1-2 ps. Our experimental observations and performed theoretical modeling allow us to conclude that this dark state can be associated with the nπ* electronic state, which is connected to the excited and ground states via conical intersections. TOC

The ultrafast excited-state dynamics of flavin mononucleotide (FMN) was monitored upon light irradiation by a hybrid experimental/computational approach.

We determined the complete relaxation dynamics of pyrene in ethanol from the second bright state, employing experimental and theoretical broadband heterodyne detected transient grating and two-dimensional photon echo (2DPE) spectroscopy, using pulses with duration of 6 fs and covering a spectral range spanning from 250 to 300 nm. Multiple lifetimes are assigned to conical intersections through a cascade of electronic states, eventually leading to a rapid population of the lowest long-living excited state and subsequent slow vibrational cooling. The lineshapes in the 2DPE spectra indicate that the efficiency of the population transfer depends on the kinetic energy deposited into modes required to reach a sloped conical intersection, which mediates the decay to the lowest electronic state. The presented experimental–theoretical protocol paves the way for studies on deep-ultraviolet-absorbing biochromophores ubiquitous in genomic and proteic systems.