How a linear triazene photoisomerizes in a volume-conserving fashion.

Understanding deactivation mechanisms of functional groups is a key step to design novel photo-active devices and molecular imaging agents. Here, we elucidate the photochemistry of linear triazenes, an extended analogue of the photo-switchable azo group, exemplarily for the widely used DNA-minor-groove binder berenil. Combining ultrafast spectroscopy and ab initio calculations unveils that the E-azo,s-trans structure of berenil predominates in the gas phase and in aqueous solution, and ADC(2) intrinsic reaction coordinate calculations disclose that the excited-state relaxation to the S1 minima/conical intersections follows a two-step mechanism: N[double bond, length as m-dash]N bond stretching followed by a bicycle-pedal rotation in the triazene bridge.

Impact of kilobar pressures on ultrafast triazene and thiacyanine photodynamics.

Very short fluorescence lifetimes evidence ultrafast deactivation of photoexcited molecules. To unveil the underlying mechanism for two compounds exhibiting (sub)picosecond emission dynamics, we combine femtosecond fluorescence upconversion with high-pressure liquid-phase spectroscopy. For the triazene berenil, the absence of a pressure dependence corroborates a bicycle-pedal motion as deactivating process.

Ultrafast Dynamics of a Triazene: Excited-State Pathways and the Impact of Binding to the Minor Groove of DNA and Further Biomolecular Systems.

Many synthetic DNA minor groove binders exhibit a strong increase in fluorescence when bound to DNA. The pharmaceutical-relevant berenil (diminazene aceturate) is an exception with an extremely low fluorescence quantum yield (on the order of 10). We investigate the ultrafast excited-state dynamics of this triazene by femtosecond time-resolved fluorescence experiments in water, ethylene glycol, and buffer and bound to the enzyme β-trypsin, the minor groove of AT-rich DNA, and G-quadruplex DNA.

Resolving Vibrational from Electronic Coherences in Two-Dimensional Electronic Spectroscopy: The Role of the Laser Spectrum.

The observation of coherent quantum effects in photosynthetic light-harvesting complexes prompted the question whether quantum coherence could be exploited to improve the efficiency in new energy materials. The detailed characterization of coherent effects relies on sensitive methods such as two-dimensional electronic spectroscopy (2D-ES). However, the interpretation of the results produced by 2D-ES is challenging due to the many possible couplings present in complex molecular structures.