Newton-X is an open-source computational platform to perform nonadiabatic molecular dynamics based on surface hopping and spectrum simulations using the nuclear ensemble approach. Both are among the most common methodologies in computational chemistry for photophysical and photochemical investigations. This paper describes the main features of these methods and how they are implemented in Newton-X. It emphasizes the newest developments, including zero-point-energy leakage correction, dynamics on complex-valued potential energy surfaces, dynamics induced by incoherent light, dynamics based on machine-learning potentials, exciton dynamics of multiple chromophores, and supervised and unsupervised machine learning techniques. Newton-X is interfaced with several third-party quantum-chemistry programs, spanning a broad spectrum of electronic structure methods.
We present an implementation
of the Frenkel exciton model in the
framework of the semiempirical floating occupation molecular orbitals-configuration
interaction (FOMO-CI) electronic structure method, aimed at simulating
the dynamics of multichromophoric systems, in which excitation energy
transfer can occur, by a very efficient approach. The nonadiabatic
molecular dynamics is here dealt with by the surface hopping method,
but the implementation we proposed is compatible with other dynamical
approaches. The exciton coupling is computed either exactly, within
the semiempirical approximation considered, or by resorting to transition
atomic charges. The validation of our implementation is carried out
on the
trans
-azobenzeno-2S-phane (2S-TTABP), formed
by two azobenzene units held together by sulfur bridges, taken as
a minimal model of multichromophoric systems, in which both strong
and weak exciton couplings are present.
We performed computational simulations of the photodynamics of a self assembled monolayer (SAM) of an azobenzene derivative (azobiphenyl, ABPT) on a gold surface. An excitonic approach was adopted in a semiempirical framework, which allowed to consider explicitly the electronic degrees of freedom of 12 azobenzene chromophores. The surface hopping scheme was used for the nonadiabatic molecular dynamics simulations. According to our results for an all trans-ABPT SAM, the excitation energy transfer between different chromophores, very fast in the ππ* manifold, does not occur between nπ* states. As a consequence, the excitation transfer does not play an important role in the quenching of the azobenzene photoisomerization in the SAM (experimentally observed, and reproduced by our calculations), which has instead to be attributed to steric effects.
This work describes the synthesis of photoactive proton transfer compounds based on the benzazolic core containing the azide group. The compounds present absorption in the UV region and fluorescence emission in the visible region of the spectra with large Stokes shift due to a phototautomerism in the excited state (ESIPT). The azide location on the benzazolic structure presented a noteworthy role on their photophysics, leading to fluorescence quenching. A photophysical study was performed in the presence of NaHS to evaluate their application as an H 2 S sensor. The methodology employed was the reduction of azides to amines using NaHS to mimic H 2 S, resulting in an off−on response fluorescence mechanism. The observed photophysical features were successfully used to explore the azides as fluorescent probes in biological media. In addition, DFT and TD-DFT calculations with the CAM-B3LYP/cc-pVDZ and CAM-B3LYP/jun-cc-pVTZ level, respectively, were performed in order to understand the photophysics features of azide derivatives, where the main interest was to investigate the fluorescence quenching experimentally observed in the azide derivatives.
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