Ultrafast dynamics in co-sensitized photocatalysts under visible and NIR light irradiation

Abstract

Co-sensitization to achieve a broad absorption window is a widely accepted technique in light harvesting nanohybrid synthesis. Protoporphyrin (PPIX) and squaraine (SQ2) are two organic sensitizers absorbing in the visible and NIR wavelength regions of the solar spectrum, respectively. In the present study, we have sensitized zinc oxide (ZnO) nanoparticles using PPIX and SQ2 simultaneously for their potential use in broad-band solar light harvesting in photocatalysis. Förster resonance energy transfer (FRET) from PPIX to SQ2 in close proximity to the ZnO surface has been found to enhance visible light photocatalysis. In order to confirm the effect of intermolecular FRET in photocatalysis, the excited state lifetime of the energy donor dye PPIX has been modulated by inserting d10 (ZnII) and d7 (CoII) metal ions in the central position of the dye (PP(Zn) and PP(Co)). In the case of PP(Co)-SQ2, extensive photo-induced ligand to metal charge transfer counteracts the FRET efficiency while efficient FRET has been observed for the PP(Zn)-SQ2 pair. This observation has been justified by the comparison of the visible light photocatalysis of the respective nanohybrids with several control studies. We have also investigated the NIR photocatalysis of the co-sensitized nanohybrids which reveals that reduced aggregation of SQ2 due to co-sensitization of PPIX increases the NIR photocatalysis. However, core-metalation of PPIX reduces the NIR photocatalytic efficacy, most probably due to excited state charge transfer from SQ2 to the metal centre of PP(Co)/PP(Zn) through the conduction band of the host ZnO nanoparticles.

Crystallization‐Induced Reversal from Dark to Bright Excited States for Construction of Solid‐Emission‐Tunable Squaraines

“…Squaraines (SQs), based on the specific central electron‐deficient four‐membered molecular architecture, act as a versatile class of functional organic dyes, which have attracted increasingly attention in both science and technology, such as bio‐imaging, nonlinear optics, photovoltaics, photodynamic therapy, chemo‐/bio‐sensing, and photocatalysis . Although tremendous progress in SQs has been achieved, most of them are focused on synthesis work and photophysical investigation in solution or dispersed state .…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Natural dyes, in particular, anthocyanin extracted from Karkade (Hibiscus) flowers, have been associated with ZnO as an effective sensitizer to eliminate E. coli bacteria and mineralize their organic components under simulated solar light [83]. Attempts to extend the ZnO sensitization to the near-infrared (NIR) region have been reported, thanks to conjugation with cyanine dye (IR820) [93], protoporphyrin (PPIX), or squaraine dye (SQ2) [80]. Finally, the interfacial charge transfer between a coumarin dye and ZnO quantum dots was studied by transient absorption and DFT, identifying a rather direct electron transfer mechanism [94].…”

Inkjet‐Printed Conductive ITO Patterns for Transparent Security Systems

“…One can assume that higher temperatures are obtained on the surface of the ITO film due to the increased absorption by the dye layer. [ 36 ] In order to prove this assumption, the temperature simulations were carried out with the SimPulse software. According to simulations (Figure S2, Supporting Information), the presence of the SQ2 dye elevates the surface temperature of the ITO film up to 600 °C during FLA pulses that last for 0.2 ms each.…”