Derivatized Benzothiazoles as Two-Photon-Absorbing Organic Photosensitizers Active under Near Infrared Light Irradiation

Abstract

Homogeneous organic photocatalysis typically requires molecular photosensitizers absorbing in the ultraviolet–visible (UV/vis) region, because UV/vis photons possess the sufficient energy to excite those one-photon-absorbing photosensitizers to the desired excited states. However, UV/vis light irradiation has many potential limitations, especially for large-scale applications, such as low penetration through reaction media, competing absorption by substrates and co-catalysts, and incompatibility with substrates bearing light-sensitive functionalities. In fact, these drawbacks can be effectively avoided if near infrared (NIR) photons can be utilized to drive the target reactions. Herein, we report two benzothiazole-derived compounds as novel two-photon-absorbing (TPA) organic photosensitizers, which can function under NIR light irradiation using inexpensive LED as the light source. We demonstrate that by judicially modulating the donor−π–acceptor−π–donor-conjugated structure containing a bibenzothiazole core and imine bridges, excellent two-photon absorption capability in the NIR region can be achieved, approaching 2000 GM at 850 nm. Together with large quantum yields (∼0.5), these benzothiazole-derived TPA organic photosensitizers exhibit excellent performance in driving various O2-involved organic reactions upon irradiation at 850 nm, showing great penetration depth, superior to that upon blue light irradiation. A suite of photophysical and computational studies were performed to shed light on the underlying electronic states responsible for the observed TPA capability. Overall, this work highlights the promise of developing Ru/Ir-free organic photosensitizers operative in the NIR region by taking advantage of the two-photon absorption mechanism.

Shedding Light on Benzo[d]pyrrolo[2,1-b]thiazole-3-carbonitrile Sensitizer-Based TiO2 Photocatalysts for Enhanced Hydrogen Generation

“…According to the obtained data, the BP dyes exhibit two absorbance bands, one that is short-wavelength at 354 nm and the other that is long-wavelength at 403 nm, which can be attributed to the π–π* electronic transition of the double bonds and the n−π* electronic transition of the lone pair electrons on the substituted cyano group, respectively. These results clearly indicate that the basic consecutive structure of the dyes that were used in this study is similar. − UV–vis diffuse reflectance spectra of the dye-loaded platinized TiO 2 composites TiO 2 –BP-1, TiO 2 –BP-2, and TiO 2 –BP-3 are shown in Figure b and Table . Here, weak absorption bands in the 430–450 nm range are observed, showing an enhancement of the position of the absorption band at 410–430 nm for platinized TiO 2 .…”

“…BTA derivatives are essentially used as dye sensitizers, as well as in the area of chemical research that includes drug development and polymer chemistry. − For these native molecules, it is observed that light absorption typically occurs between 300–410 nm. However, by substituting suitable withdrawing or donating groups at the appropriate positions of a BTA derivative, light absorption can be enhanced in the visible region as well. , The CN acceptor group, which is present in all three of the dyes, directly bonds to the TiO 2 surface via a NC–O–Ti–O linkage . In this study, a significant hydrogen generation rate of 3.32 mmol g –1 h –1 , with an apparent quantum yield (AQY) of 8.5% and a turnover number (TON) of 3344, was obtained for TiO 2 –BP-1 at 420 nm.…”

Removal of Tetracycline Hydrochloride by Photocatalysis Using Electrospun PAN Nanofibrous Membranes Coated with g-C3N4/Ti3C2/Ag3PO4

“…Therefore, it is urgent to develop a solar-driven catalyst for the efficient degradation of antibiotic pollutants in water. Metal-free organic photocatalysis merges organic synthesis with photochemistry and enables many challenging organic transformations to take place under ambient conditions while using photon as the sole energy source [ 6 ]. g-C 3 N 4 is a new metal-free polymer visible light-driven semiconductor photo-catalyst [ 7 , 8 , 9 ], which can absorb visible light with wavelength less than 470 nm and has irreplaceable advantages.…”

Identification of Blood Transport Proteins to Carry Temoporfin: A Domino Approach from Virtual Screening to Synthesis and In Vitro PDT Testing

“…Photodynamic therapy (PDT) is a minimally invasive therapeutic modality, clinically approved for treating several types of cancer [ 1 , 2 , 3 , 4 ]. PDT is based on the use of a drug, called photosensitizer (PS) [ 1 , 2 , 3 , 4 , 5 ], that is activated by light absorption to react with the oxygen normally present in cells/tissues, generating oxidative stress that causes (i) direct cytotoxicity on cancer cells; (ii) damages to the tumor vascular system; (iii) and the stimulation of an immune response [ 1 , 2 , 3 , 4 ].…”