On the possibility of electronically excited states in stable amine anions: Dicyanoamine, cyanoethynylamine, and diethynylamine

Front. Astron. Space Sci.

2021

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Functionalizing deprotonated polycyclic aromatic hydrocarbon (PAH) anion derivatives gives rise to electronically excited states in the resulting anions. While functionalization with −OH and −C2H, done presently, does not result in the richness of electronically excited states as it does with −CN done previously, the presence of dipole-bound excited states and even some valence excited states are predicted in this quantum chemical analysis. Most notably, the more electron withdrawing −C2H group leads to valence excited states once the number of rings in the molecule reaches three. Dipole-bound excited states arise when the dipole moment of the corresponding neutral radical is large enough (likely around 2.0 D), and this is most pronounced when the hydrogen atom is removed from the functional group itself regardless of whether functionalized by a hydroxyl or enthynyl group. Deprotonatation of the hydroxyl group in the PAH creates a ketone with a delocalized highest occupied molecular orbital (HOMO) unlike deprotonation of a hydrogen on the ring where a localized lone pair on one of the carbon atoms serves as the HOMO. As a result, hydroxyl functionlization and subsequent deprotonation of PAHs creates molecules that begin to exhibit structures akin to nucleic acids. However, the electron withdrawing −C2H has more excited states than the electron donating −OH functionalized PAH. This implies that the −C2H electron withdrawing group can absorb a larger energy range of photons, which signifies an increasing likelihood of being stabilized in the harsh conditions of the interstellar medium.

Section: Introductionsupporting

confidence: 78%

Section: Relative Energies and Dipole Momentsmentioning

confidence: 88%

Electronically Excited States of Potential Interstellar, Anionic Building Blocks for Astrobiological Nucleic Acids

Santaloci

Strauss

Front. Astron. Space Sci.

2021

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“…These bases are used for all single point calculations to fully account for the diffuseness of the electron density in potentially highly-diffuse states around the molecule. Additionally, since the computational cost scales up with the size of the molecule, a set of 6s, 6p, 2d diffuse functions located about the center-of-mass are utilized in conjunction with the aug-cc-pVDZ and aug-cc-pVTZ basis sets to compute the excited state properties of all four systems 68,70,71 and are written in shorthand as DZ+spd and TZ+spd.…”

Section: Methodsmentioning

confidence: 99%

Highly-excited state properties of cumulenone chlorides in the vacuum-ultraviolet

Nguyen

Peters

Phys. Chem. Chem. Phys.

2020

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Electronically excited states of closed-shell azabenzene and purine anion structures: Is 2 D enough for dipole-bound excited states?

Santaloci

The Journal of Chemical Physics

2023

Deprotonated azabenzene anions require dipole moments in their corresponding neutral radicals of more than 3.5 D in order to exhibit dipole-bound excited states (DBXSs). This is notably larger than the typical 2.0 D to 2.5 D associated with such behavior. Similar computational analysis on deprotonated purine derivatives also conducted herein only requires the more traditional 2.5 D dipole moment implying that the single six-membered azabenezene rings have additional factors at play in binding diffuse electrons. The present study also shows that use of coupled cluster singles and doubles with a double-zeta correlation consistent basis set and additional diffuse functions originating from the center-of-charge for all aspects of the computations decreases the error in predicting DBXSs to less than 0.006 eV at worst and likely less than 0.003 eV for most cases. These results can influence the modeling of molecular spectra beyond fundamental chemical curiosity with application to astrochemistry, solar energy harvesting, and combustion chemistry among others.