Abstract
Nonlinear optical techniques as two-photon absorption (TPA) have raised relevant interest within the last years due to the capability to excite chromophores with photons of wavelength equal to only half of the corresponding one-photon absorption energy. At the same time, its probability being proportional to the square of the light source intensity, it allows a better spatial control of the light-induced phenomenon. Although a consistent number of experimental studies focus on increasing the TPA cross section, very few of them are devoted to the study of photochemical phenomena induced by TPA. Here, we show a design strategy to find suitable E/Z photoswitches that can be activated by TPA. A theoretical approach is followed to predict the TPA cross sections related to different excited states of various photoswitches’ families, finally concluding that protonated Schiff-bases (retinal)-like photoswitches outperform compared to the others. The donor-acceptor substitution effect is therefore rationalized for the successful TPA activatable photoswitch, in order to maximize its properties, finally also forecasting a possible application in optogenetics. Some experimental measurements are also carried out to support our conclusions.
Highlights
The interest on light activated chemical reactions and processes has risen in the last decades, mainly motivated by the clear advantages of light as an external agent over chemical, thermal, or electrochemical stimuli
We have studied non-linear optical properties, and two-photon absorption (TPA), for different families of molecular photoswitches, with the goal of selecting the chromophore with the largest cross-section coupled with the most red-shifted absorption energy and the preservation of the switching efficiency
We have found two relevant results: (1) among all possible topologies of the electronic transitions, the D-π-A-π-D was found to be the most effective in increasing the value of the TPA cross section; (2) the protonated Schiff base- like switch clearly outperforms the other families
Summary
The interest on light activated chemical reactions and processes has risen in the last decades, mainly motivated by the clear advantages of light as an external agent over chemical, thermal, or electrochemical stimuli. Solar light can be exploited as a renewable energy source, while the lasers used for irradiation present high spatial and temporal resolution These facts have led to a wide variety of photochemical applications, ranging from biology to material sciences. Scientists have focused their efforts on discovering novel photochemical reactions, and on taking advantage of the ones already known to build useful building blocks [1,2,3,4,5]. Photoactive molecular devices, such as molecular motors, rotors, or switches, 4.0/). For aa molecule molecule under under linearly linearly polarized polarized light light (as we we considered considered in in this this work), work), we we can can TPA ), as follows [77]: express the TPA probability in atomic units
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