Multiple Verdazyl Radicals Appended to a Triarylamine Scaffold

We report the synthesis of three triphenylamine-based verdazyl radicals. These include a mono, bis, and tris(verdazyl) at the 4-position(s) of the N–Ar groups, containing one, two, and three unpaired electrons, respectively. Each of these compounds is air stable, and fully characterized using EPR spectroscopy, high-resolution mass spectrometry, infrared spectroscopy, UV/Vis spectroscopy, and cyclic voltammetry. From the UV/Vis absorbance data, the optical absorbance energy gaps were found to be ~2.35 eV for all three verdazyl-containing compounds. Cyclic voltammetry was used to estimate the energy levels of the singly occupied molecular orbitals (SOMOs), which are -4.91 eV, -5.12 eV, and -4.98 eV for mono, bis, and tris(verdazyl) compounds respectively. Spin-spin exchange interactions were observed in the EPR spectra of both the bis and tris(verdazyl)s, leading to additional hyperfine coupling patterns and assignment of the ground states as triplet and quartet, respectively

Singlet fission in pentacene dimers

Singlet fission (SF) has the potential to supersede the traditional solar energy conversion scheme by means of boosting the photon-to-current conversion efficiencies beyond the 30% Shockley–Queisser limit. Here, we show unambiguous and compelling evidence for unprecedented intramolecular SF within regioisomeric pentacene dimers in room-temperature solutions, with observed triplet quantum yields reaching as high as 156 ± 5%. Whereas previous studies have shown that the collision of a photoexcited chromophore with a ground-state chromophore can give rise to SF, here we demonstrate that the proximity and sufficient coupling through bond or space in pentacene dimers is enough to induce intramolecular SF where two triplets are generated on one molecule

Solution-based intramolecular singlet fission in cross-conjugated pentacene dimers

We show unambiguous and compelling evidence by means of pump–probe experiments, which are complemented by calculations using ab initio multireference perturbation theory, for intramolecular singlet fission (SF) within two synthetically tailored pentacene dimers with cross-conjugation, namely XC1 and XC2. The two pentacene dimers differ in terms of electronic interactions as evidenced by perturbation of the ground state absorption spectra stemming from stronger through-bond contributions in XC1 as confirmed by theory. Multiwavelength analysis, on one hand, and global analysis, on the other hand, confirm that the rapid singlet excited state decay and triplet excited state growth relate to SF. SF rate constants and quantum yields increase with solvent polarity. For example, XC2 reveals triplet quantum yields and rate constants as high as 162 ± 10% and (0.7 ± 0.1) × 1012 s−1, respectively, in room temperature solutions