Exploring chemical space in the search for improved azoheteroarene-based photoswitches

Vela, Sergi; Krüger, Constantin; Corminbœuf, Clémence

doi:10.1039/c9cp03831k

“…The initial assessment of the vertical nπ* (S1) and ππ* excitations (S2) of 1-2a at the respective E-isomer minima ( Figure 1) shows no significant difference between 1 and 2, whereas the ππ* is significantly red-shifted in 2a by the increased charge-transfer character from the thiazine to the azo group. 36 The shift is also clearly visible in the absorption spectra computed at the same level (i.e., ωB97X-D/6-31G(d) level, see Figure 2 and Comp. Details), which includes the conformational and vibrational transitions with the Nuclear Ensemble (NE) approach.…”

Section: Introductionmentioning

confidence: 79%

“…Minimal energy crossing points were computed with CIOPT 45 interfaced with Gaussian 09 (G09). 50 Based on previous benchmarks, 36,51,52 we used TD-DFT within the Tamm-Dancoff approximation (TDA), the ωB97X-D functional 53,54 and the 6-31G(d) basis set. The Non-Adiabatic Molecular Dynamics (NAMD) simulations were performed with Newton-X 55,56 interfaced with G09.…”

Section: Computational Detailsmentioning

confidence: 99%

The Photoisomerization Pathway(s) of Push-Pull Phenylazoheteroarenes

Vela¹,

Corminbœuf²

2020

Preprint

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<div> Azoheteroarenes are the most recent derivatives targeted to further improve the properties of azo-based photoswitches. Their light-induced mechanism for trans-cis isomerization is assumed to be very similar to that of the parent azobenzene. As such, they inherited from the controversy about the dominant isomerization pathway (rotation vs. inversion) depending on the excited state (nπ* vs. ππ*). While the controversy seems settled in azobenzene, the extent to which the same conclusions apply to the more structurally-diverse family of azoheteroarenes is unclear. Here, we unravel by means of non-adiabatic molecular dynamics, the photoisomerization mechanism of three prototypical phenyl-azoheteroarenes with an increasing push-pull character. The evolution of the rotational and inversion conical intersection energies, the preferred pathway, and the associated kinetics upon both nπ* and ππ* excitations can be linked directly with the push-pull substitution effects. Overall, we clarify the working conditions of this family of azo-dyes and identify a possibility to exploit push-pull substituents to tune their photoisomerization quantum yield. </div>

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“…that both AB and ppAB could be regarded as the reference), 8,26,48 it is hardly possible to anticipate the preferred thermal relaxation pathway of the systems studied herein. Therefore, we considered both inversion and rotation as possible mechanisms.…”

Section: Rotation Vs Inversion Mechanism Of Thermal Relaxationmentioning

confidence: 98%

Tuning the Thermal Stability and Photoisomerization of Azoheteroarenes through Macrocycle Strain

Vela¹,

Scheidegger²,

Fabregat³

et al. 2020

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Azobenzene and its derivatives are one of the most-widespread molecular scaffolds in a range of modern applications, as well as in fundamental research. After photoexcitation, azo-based photoswitches revert back to the most stable isomer in a timescale (t1/2) that determines the range of potential applications. Attempts to bring t1/2 to extreme values prompted to the development of azobenzene and azoheteroarene derivatives that either rebalance the E- and Z- isomer stabilities, or exploit unconventional thermal isomerization mechanisms. In the former case, one successful strategy has been the creation of macrocycle strain, which tends to impact the E/Z stability asymmetrically, and thus significantly modifies t1/2. On the bright side, bridged derivatives have shown an improved optical switching owing to the higher quantum yields and absence of degradation. However, in most (if not all) cases, bridged derivatives display a reversed thermal stability (more stable Z-isomer), and smaller t1/2 than the acyclic counterparts, which restricts their potential interest to applications requiring a fast forward and backwards switch. In this paper, we investigate the impact of alkyl bridges to the thermal stability of phenyl-azoheteroarenes using computational methods, and we reveal that is indeed possible to combine such improved photo-switching characteristics while preserving the regular thermal stability (more stable E-isomer), and increased t1/2 values under the appropriate connectivity and bridge length.

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“…The Non-Adiabatic Molecular Dynamics (NAMD) simulations were performed with Newton-X 54,55 interfaced with G09. 56 Based on previous benchmarks, 26,57,58 we used linear-response TDDFT 59,60 within the Tamm-Dancoff approximation (TDA), the ωB97X-D functional 61,62 and the 6-31G(d) basis set. 500 Initial conditions were generated from the Wigner distribution based on the harmonic oscillator, four states (S0-S3), a Lorentzian broadening of 0.1 eV, an anharmonicity factor of 3, and a temperature of 300 K. From these initial conditions, we obtain the initial geometries and velocities for the trajectories.…”

Section: Computational Detailsmentioning

confidence: 99%

“…Therefore, for the main discussion we prioritized the results with ωB97X-D for the sake of its better description of the photochemistry of azo-dyes. 26,57,58 Interestingly, the rotational pathway is systematically much faster than inversion. The greatest difference between pathways is found for the acyclic azoheteroarenes, with / in the order of 30 and 3 seconds for 1 and 2, respective (compared to 321 and 89 days for inversion).…”

Section: (Acyclic)mentioning

confidence: 99%

Tuning the Thermal Stability and Photoisomerization of Azoheteroarenes through Macrocycle Strain

Vela¹,

Scheidegger²,

Fabregat³

et al. 2020

Preprint

Self Cite

0

View full text Add to dashboard Cite

Azobenzene and its derivatives are one of the most-widespread molecular scaffolds in a range of modern applications, as well as in fundamental research. After photoexcitation, azo-based photoswitches revert back to the most stable isomer in a timescale (t1/2) that determines the range of potential applications. Attempts to bring t1/2 to extreme values prompted to the development of azobenzene and azoheteroarene derivatives that either rebalance the E- and Z- isomer stabilities, or exploit unconventional thermal isomerization mechanisms. In the former case, one successful strategy has been the creation of macrocycle strain, which tends to impact the E/Z stability asymmetrically, and thus significantly modifies t1/2. On the bright side, bridged derivatives have shown an improved optical switching owing to the higher quantum yields and absence of degradation. However, in most (if not all) cases, bridged derivatives display a reversed thermal stability (more stable Z-isomer), and smaller t1/2 than the acyclic counterparts, which restricts their potential interest to applications requiring a fast forward and backwards switch. In this paper, we investigate the impact of alkyl bridges to the thermal stability of phenyl-azoheteroarenes using computational methods, and we reveal that is indeed possible to combine such improved photo-switching characteristics while preserving the regular thermal stability (more stable E-isomer), and increased t1/2 values under the appropriate connectivity and bridge length.

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Exploring chemical space in the search for improved azoheteroarene-based photoswitches

Abstract: A computational screening of azoheteroarenes identifies good candidates and provides guidelines on how to tune their performance through chemical substitution.

Cited by 18 publications

References 46 publications

The Photoisomerization Pathway(s) of Push-Pull Phenylazoheteroarenes

The Photoisomerization Pathway(s) of Push-Pull Phenylazoheteroarenes

Tuning the Thermal Stability and Photoisomerization of Azoheteroarenes through Macrocycle Strain

Tuning the Thermal Stability and Photoisomerization of Azoheteroarenes through Macrocycle Strain

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