Thienyl/phenyl bay-substituted perylenebisimides: Intersystem crossing and application as heavy atom-free triplet photosensitizers

Origins of Molecular-Twist-Triggered Intersystem Crossing in Functional Perylenediimides: Singlet–Triplet Gap versus Spin–Orbit Coupling

“…Eco-friendly, heavy-atom-free small organic molecules are promising candidates because of their easily tunable physiochemical properties and flexibility. However, negligibly small SOC in these systems leads to inefficient ISC, restricting their practical use as triplet photosensitizers. − Conventionally, a large SOC is achieved by an internal heavy-atom effect. , In addition, strategies such as substitutional doping with light hetero-elements (for example, “N”), defects, dielectric screening, and also introducing geometrical strains were shown to improve the ISC/RISC rates. − Significantly enhanced ISC was reported for heavy-atom-free perylenediimide (PDI) bay-substituted with electron-donor units. , A considerable ISC rate was also reported for a geometrically twisted phenanthrene-fused PDI, whereas the corresponding planar analogue produced a negligibly small ISC rate . PDI functionalized with anthryl and carbazole at the bay positions exhibits long lived triplet with substantially high triplet quantum yield (Φ T ) .…”

Silylethynyl Substitution for Preventing Aggregate Formation in Perylene Diimides

“…22,23 The transitions associated with the lowest energy excitonic states are critical to the performance of organic photonic devices, 19,24,25 with deactivation and quenching by dimer 26,27 or excimer 28,29 states able to outcompete many desired processessuch as charge transfer and transport, 30 exciton diffusion, 31 and intersystem crossing. 26,27,32 PDIs that form such excimer, dimer, or aggregate states also often exhibit significantly different photophysical properties compared to isolated molecules, making understanding and developing device applications complicated at higher concentrations. 33 For example, redshifted photoluminescence (PL) spectrum, increased fluorescence lifetime, and losses in PLQYs are all commonly reported.…”

“…The superior optical properties of PDIs and other flat polycyclic aromatic hydrocarbon molecules in solution phase are often not preserved in films due to aggregation-caused quenching (ACQ). , The same is also true for regular perylenes, which are often used as blue emitters and for triplet–triplet annihilation applications. , The transitions associated with the lowest energy excitonic states are critical to the performance of organic photonic devices, ,, with deactivation and quenching by dimer , or excimer , states able to outcompete many desired processessuch as charge transfer and transport, exciton diffusion, and intersystem crossing. ,, PDIs that form such excimer, dimer, or aggregate states also often exhibit significantly different photophysical properties compared to isolated molecules, making understanding and developing device applications complicated at higher concentrations . For example, redshifted photoluminescence (PL) spectrum, increased fluorescence lifetime, and losses in PLQYs are all commonly reported. ,− The deleterious effects of high-concentration multimolecular interactions and ACQ are further amplified in systems where dyes are anchored at high loading onto nanoparticle surfaces as ligands, with such dye-particle composite materials generating strong interest for light-harvesting and photon conversion applications. , …”

Two-photon absorption and triplet excited state quenching of near-IR region aza-BODIPY photosensitizers via a triphenylamine moiety despite heavy bromine atoms

“…1. However, our previous studies 24,54–58 revealed that the fluorescence signal is negligibly low when the charge transfer occurs due to the presence of strong electron-donating groups such as triphenylamine and the phenolate form of hydroxy groups. In these studies, emission characteristics and the charge transfer relationship were discussed in detail.…”