Spectroscopic signatures of triplet states in acenes

Abstract

Triplet states are of great interest in current light-energy conversion strategies, as their creation through the singlet fission processes can overcome the Shockley-Queisser limit. We analyze the experimental possibilities for the detection of triplet states with ground state and linear response time dependent density functional calculations. We show that triplets can be clearly detected through their optical properties, that can be seen in photoabsorption and photeoelectron spectra, as well as in vibrational properties, that can be studied via infrared spectra.

Singlet oxygen quantum yields and photostability of planar binuclear phthalocyanines

“…The smaller S 1 -T 1 energy difference in the case of Zn2 can be explained by a weaker exchange interaction between unpaired electrons in S 1 and T 1 excited states as a result of their delocalization over larger p-system. A similar but weaker trend is observed for oligoacenes [30]. The photooxidative stabilities of phthalocyanines were investigated earlier [31,32].…”

2,3‐Dichloroanthracene crystal, a new rigid matrix for single molecule optical investigations

“…Although the calculated spin‐orbit coupling between the T 1 and S 0 states in 23DCA is only 0.22 cm −1 , and is much less than the coupling calculated for 23DBN (4 cm −1 ), the extremely low yield of the intersystem crossing, S 1 →T 1 , in 23DCA seems to be crucial. It was already experimentally and theoretically considered, that this process in acenes is dependent on the relative positions of the S 1 and T 2 states [18–20] . The direct intersystem crossing S 1 → T 1 is weak, and in case of a molecule with its S 1 state below the T 2 , observation of phosphorescence would require thermal activation (which may operate at elevated temperatures) [21] …”

“…Thus, the decision as to the intersystem crossing path has to rely on the experiment, already well known problem in the literature. [18][19][20] In our case phosphorescence of 23DCA was too weak to be observed, suggesting that the singlet S 1 state is located below the triplet T 2 .…”

“…It was already experimentally and theoretically considered, that this process in acenes is dependent on the relative positions of the S 1 and T 2 states. [18][19][20] The direct intersystem crossing S 1 ! T 1 is weak, and in case of a molecule with its S 1 state below the T 2 , observation of phosphorescence would require thermal activation (which may operate at elevated temperatures).…”

Macroscopic Quantum Electrodynamics and Density Functional Theory Approaches to Dispersion Interactions between Fullerenes

“…The Kohn-Sham approach further introduces effective single-particle molecular orbitals (MO) from which the exact electron density can be determined. While orbitals lack a clearly defined meaning, it is well known that they resemble measurable properties of many-body system if single particle properties such as photoelectron energies [38,39], angular distributions [40] or scanning tunneling microscopy images [41,42] are considered. The single particle picture can also fail for these observables, however [43,44].…”