Permanent Dipole Moments Enhance Electronic Coupling and Singlet Fission in Pentacene

Abstract

Singlet fission (SF), the photophysical process in which one singlet exciton is transformed into two triplets, depends inter alia on the coupling of electronic states. Here, we use fluorination and the resulting changes in partial charge distribution across the chromophore backbone as a particularly powerful tool to control this parameter in pentacene. We find that the introduction of a permanent dipole moment leads to an enhanced coupling of Frenkel exciton and charge transfer states and to an increased SF rate which we probed using ultrafast transient absorption spectroscopy. These findings are contrasted with H-aggregate formation and a significantly reduced triplet-pair state lifetime in a fluorinated pentacene for which the different partial charge distribution leads to a negligible dipole moment.

Modeling the electronic structure of organic materials: a solid-state physicist’s perspective

“…The value of the fundamental gap in the cluster, 6.66 eV, is less than 0.3 eV smaller than the one computed for the isolated molecule. This result, in line with previous findings obtained at the same level of theory for longer oligoacenes [132], is unsurprising and confirms that the band-gap reduction seen in the crystal cannot be captured with such a minimal model. Yet, as discussed in section 4, a convenient shortcut is available for an accurate evaluation of this quantity at affordable computational costs, without the need to simulating the full periodic crystal.…”

Semiconductor Porous Hydrogen-Bonded Organic Frameworks Based on Tetrathiafulvalene Derivatives

“…The energy splitting between the highest-occupied crystal orbitals involving the two TTFs of the unit cell (VBM energy splitting) was evaluated as a bare approximation of the electronic communication between TTF pairs, showing a larger mean value for zwitterionic MUV-20a (175 meV) and MUV-20b (158 meV) than for MUV-21 (90 meV). Accurate electronic couplings for the closest interacting TTF pairs (dimer A in Figure ) confirm this picture, with J values of 152, 92, and 55 meV for MUV-20a , MUV-20b , and MUV-21 , respectively, which are in the same order of magnitude of those reported for prototypical organic semiconductors. , The coupling in the weakly interacting TTF pair (dimer B) is predicted one order of magnitude smaller (14, 37, and 7 meV for MUV-20a , MUV-20b , and MUV-21 , respectively), which stems from the less efficient π-stacking of the TTF moieties (core-to-core intermolecular distances > 5 Å; Figure ). Overall, considering the smaller electronic coupling as the limiting step for charge conduction, we predict rate constants of 8 × 10 10 , 6 × 10 11 , and 2 × 10 10 s –1 for MUV-20a , MUV-20b , and MUV-21 , respectively (Table S14).…”

“…Accurate electronic couplings for the closest interacting TTF pairs (dimer A in Figure 7) confirm this picture, with J values of 152, 92, and 55 meV for MUV-20a, MUV-20b, and MUV-21, respectively, which are in the same order of magnitude of those reported for prototypical organic semiconductors. 51,52 The coupling in the weakly interacting TTF pair (dimer B) is predicted one order of magnitude smaller (14, 37, and 7 meV for MUV-20a, MUV-20b, and MUV-21, respectively), which stems from the less efficient π-stacking of the TTF moieties (core-to-core intermolecular distances > 5 Å; Figure 7). Overall, considering the smaller electronic coupling as the limiting step for charge conduction, we predict rate constants S14).…”

Design of BPEA-based derivatives with high singlet fission performance: a theoretical perspective

“…The reported SF materials usually have large alternant hydrocarbons, e.g. acene derivatives (pentacene, tetracene, and hexacene), 16,24 rubrene, 17,25 carotenoids, 26,27 conjugated polymers, 28,29 biradicaloids, 30 etc. Most of them have a very low triplet quantum yield and slow SF rate.…”