Electronic Relaxation Pathways in Heavy-Atom-Free Photosensitizers Absorbing Near-Infrared Radiation and Exhibiting High Yields of Singlet Oxygen Generation

Abstract

Heavy-atom-free photosensitizers (HAF-PSs) based on thionation of carbonyl groups of readily accessible organic compounds are rapidly emerging as a versatile class of molecules. However, their photochemical properties and electronic relaxation mechanisms are currently unknown. Investigating the excited-state dynamics is essential to understand their benefits and limitations and to develop photosensitizers with improved photochemical properties. Herein, the photochemical and electronic-structure properties of two of the most promising HAF-PSs developed to date are revealed. It is shown that excitation of thio-4-(dimethylamino)naphthalamide and thionated Nile Red with near-infrared radiation leads to the efficient population of the triplet manifold through multiple relaxation pathways in hundreds of femtoseconds. The strong singlet−triplet couplings in this family of photosensitizers should enable a broad range of applications, including in photodynamic therapy, photocatalysis, photovoltaics, organic LEDs, and photon up-conversion.

Excited-State Modulation of Aggregation-Induced Emission Molecules for High-Efficiency Triplet Exciton Generation

“…An ultrafast internal conversion thus occurs, in ca. 0.5 ps in cyclohexane and 2 ps in dioxane . This ultrafast component is apparent looking at the kinetics, particularly those recorded below 500 nm (Figure S6).…”

Bridging D–A type photosensitizers with the azo group to boost intersystem crossing for efficient photodynamic therapy

“…This equation suggests that the increase in ξ ST and decrease in ΔE ST give rise to high k ISC and thus efficient ISC. It is well acknowledged that the introduction of heavy atoms [20][21][22][23] (e.g., bromide, iodine, selenium, or platinum) favors the increase in ξ ST . However, the presence of heavy atoms may bring in potential toxicity when used in biological systems, limiting their biomedical applications.…”

Orthogonal carbazole-perylene bisimide pentad: a photoconversion-tunable photosensitizer with diversified excitation and excited-state relaxation pathways

“…In most cases, PSs tend to support either diagnosis or therapeutics alternatively, and thereby "all-in-one" theranostic PSs with multifaceted and tunable photonic properties are preferred. Generally, incorporating heavy atoms into core structure of PSs is an effective approach to populate excited triplet states via enhanced spin-orbit-coupling, and yet the generated PSs are often suffering from increased dark cytotoxicity and potentially high cost of heavy metals [4,[9][10][11][12][13]. Therefore, the development of photoconversion-tunable heavy-atom-free PSs with advanced photonic properties is essential to refine the related applications.…”