RESUMEN
Metal-free organic emitters that display solution-phase room temperature phosphorescence (sRTP) remain exceedingly rare. Here, we investigate the structural and photophysical properties that support sRTP by comparing a recently reported sRTP compound (BTaz-Th-PXZ) to two novel analogous materials, replacing the donor group by either acridine or phenothiazine. The emissive triplet excited state remains fixed in all three cases, while the emissive charge-transfer singlet states (and the calculated paired charge-transfer T2 state) vary with the donor unit. While all three materials show dominant RTP in film, in solution different singlet-triplet and triplet-triplet energy gaps give rise to triplet-triplet annihilation followed by weak sRTP for the new compounds, compared to dominant sRTP throughout for the original PXZ material. Engineering both the sRTP state and higher charge-transfer states therefore emerges as a crucial element in designing emitters capable of sRTP.
RESUMEN
Perylene diimide (PDI) dyes are extensively investigated because of their favorable photophysical characteristics for a wide range of organic material applications. Fine-tuning of the optoelectronic properties is readily achieved by functionalization of the electron-deficient PDI scaffold. Here, we present four new donor-acceptor type dyads, wherein the electron donor units - benzo[1,2-b : 4,5-b']dithiophene, 9,9-dimethyl-9,10-dihydroacridine, dithieno[3,2-b : 2',3'-d]pyrrole, and triphenylamine-are attached to the bay-positions of the PDI acceptor. Intersystem crossing occurs for these systems upon photoexcitation, without the aid of heavy atoms, resulting in singlet oxygen quantum yields up to 80 % in toluene solution. Furthermore, this feature is retained when the system is directly irradiated with energy corresponding to the intramolecular charge-transfer absorption band (at 639â nm). Geometrical optimization and (time-dependent) density functional theory calculations afford more insights into the requirements for intersystem crossing such as spin-orbit coupling, dihedral angles, the involvement of charge-transfer states, and energy level alignment.
RESUMEN
To gauge the suitability of an organic dye for thermally activated delayed fluorescence (TADF), its excited state properties are often calculated using density functional theory. For this purpose, the choice of the exchange-correlation (XC) functional is crucial as it heavily influences the quality of the obtained results. In this work, 19 different XC functionals with various amounts of Hartree-Fock (HF) exchange and/or long-range correction parameters are benchmarked versus resolution-of-the-identity second-order coupled cluster (riCC2) calculations for a set of 10 prototype intramolecular donor-acceptor compounds. For the time-dependent density functional theory (TD-DFT) calculations, LC-BLYP(ω = 0.20) and M06-2X are the better performing XC functionals when looking at singlet and triplet excitation energies, respectively. For the singlet-triplet energy gap, LC-BLYP(ω = 0.17), LC-ωPBE(ω = 0.17) and a hybrid LC-BLYP(ω = 0.20)/M06-2X method give the smallest mean average errors (MAEs). Using the Tamm-Dancoff approximation (TD-DFT/TDA), the MAEs are further reduced for the triplet vertical excitation energies and the singlet-triplet energy gaps.
RESUMEN
Boron dipyrromethene (BODIPY) dyes represent a particular class within the broad array of potential photosensitizers. Their highly fluorescent nature opens the door for theragnostic applications, combining imaging and therapy using a single, easily synthesized chromophore. However, near-infrared absorption is strongly desired for photodynamic therapy to enhance tissue penetration. Furthermore, singlet oxygen should preferentially be generated without the incorporation of heavy atoms, as these often require additional synthetic efforts and/or afford dark cytotoxicity. Solutions for both problems are known, but have never been successfully combined in one simple BODIPY material. Here, we present a series of compact BODIPY-acridine dyads, active in the phototherapeutic window and showing balanced brightness and phototoxic power. Although the donor-acceptor design was envisioned to introduce a charge transfer state to assist in intersystem crossing, quantum-chemical calculations refute this. Further photophysical investigations suggest the presence of exciplex states and their involvement in singlet oxygen formation.
RESUMEN
Push-pull-type conjugated polymers applied in organic electronics do not always contain a perfect alternation of donor and acceptor building blocks. Misscouplings can occur, which have a noticeable effect on the device performance. In this work, the influence of homocoupling on the optoelectronic properties and photovoltaic performance of PDTSQxff polymers is investigated, with a specific focus on the quinoxaline acceptor moieties. A homocoupled biquinoxaline segment is intentionally inserted in specific ratios during the polymerization. These homocoupled units cause a gradually blue-shifted absorption, while the highest occupied molecular orbital energy levels decrease only significantly upon the presence of 75-100% of homocouplings. Density functional theory calculations show that the homocoupled acceptor unit generates a twist in the polymer backbone, which leads to a decreased conjugation length and a reduced aggregation tendency. The virtually defect-free PDTSQxff affords a solar cell efficiency of 5.4%, which only decreases substantially upon incorporating a homocoupling degree over 50%.