Dyad Sensitizer of Chlorophyll with Indoline Dye for Panchromatic Photocatalytic Hydrogen Evolution

Abstract

Photocatalytic H 2 evolution under a wide visible spectral range is a challenging issue. In this work, we report the synthesis of a novel organic dyad consisting of an indoline−rhodanine π-conjugation with a strong absorption in the green region and a chlorophyll derivative with intense absorbance in the purple and red regions. This synthetic dyad (Dyad) was employed as a photosensitizer in the TiO 2 -based system for photocatalytic H 2 evolution with Pt as the assisting catalyst and ascorbic acid (AA) as the sacrificial reagent. The Dyad-sensitized Pt/TiO 2 photocatalyst exhibited a maximum turnover number (TON) of 1044 after 6 h of continuous light irradiation (λ > 400 nm). In comparison, under the same conditions, the TONs of photocatalytic systems based on sole counterpart chlorophyll (Chl) or indoline dye (Ind) were merely 267 or 301, respectively. Moreover, the apparent quantum yield of Dyad/Pt/TiO 2 (1.27%) is much higher than those of Chl/Pt/TiO 2 (0.37%) and Ind/Pt/TiO 2 (0.20%) under 420 nm monochromatic light irradiation. The interfacial charge transfer and recombination processes between TiO 2 and Dyad, Chl, or Ind were evaluated with photocurrent responses and electrochemical impedance spectroscopy. The DFT calculations were in accordance with the observed charge recombination processes. The high photocatalytic activity of Dyad was attributed to not only an excellent light absorption ability over the whole visible range, but also an efficient electron transfer and balanced charge recombination processes between TiO 2 and Dyad. In addition, the sustained activities of the H 2 evolution systems were 78%, 84%, and 38% for Dyad, Chl, and Ind, respectively, after three 6 h illumination periods, indicating a similarly high reusability of both Dyad and Chl dyes as compared to Ind dye. This study simultaneously solves the problems of insufficient visible spectral response, poor stability, and high cost in photocatalytic water-splitting H 2 evolution.

Photocatalytic H2 Production from Water by Metal‐free Dye‐sensitized TiO2 Semiconductors: The Role and Development Process of Organic Sensitizers

“…Overall, it could be concluded that both the co-sensitized system and the physical mixed system based on Chl and Ind played a role of "1 + 1 > 2" compared to the case of utilizing each of them separately, and their dyad system was further superior due to its broad fullband absorption band, long charge lifetime, strong electron injection ability and high stability under irradiation. [84] Calixarene is a class of macrocyclic compounds composed of methylene bridged phenol units. Due to the adjustable cavity and ability to form host-guest complexes, calixarene plays an important role in the field of supramolecular chemistry as well as crown ether and cyclodextrin.…”

Semisynthetic Chlorophyll Derivatives Toward Solar Energy Applications

“…The successful attempt proved the feasibility of applying Chl derivatives as photocatalyst on water‐splitting systems. To further improve the yield of H 2 evolution, indoline dye (Ind, D102, Figure a) of which methyl ester could be successfully applied to OSC (vide supra), was covalently connected to the C17‐esterifying group of Chl‐18 as in Dyad . The Dyad‐sensitized Pt/TiO 2 photocatalyst exhibited a maximum turnover number (TON) of 1044 after 6 h under continuous light irradiation ( λ > 400 nm).…”

“…e) Schematic diagram of the preparation of ZnChl‐9/Ti 3 C 2 T x composites. Reproduced with permission . Copyright 2020, Wiley‐VCH.…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Other phenothiazine-and carbazole-based dyes were designed for the same application [60], including a D-π-A-π-A photosensitizer, with benzothiadiazole as auxiliary electron withdrawing unit [61], and, in particular, a dibenzopyrromethene (BODIPY)-conjugated phenothiazine, which gave Pt/TiO 2 high activity up to near-infrared (NIR) region [62]. Different types of photoactive compounds can be included in the design of a dye with specific structure: some D-A-π-A perylene dyes, featuring cyanoacrylic acid and dicyanomethylene rhodamine as the acceptor/anchoring group, combined with a N-annulated perylene donor and a quinoxaline auxiliary acceptor [63]; two triphenylamine-benzimidazole-based dyes bound on TiO 2 , with Cu 2 WS 4 nanocubes as an alternative water splitting co-catalyst to Pt [64]; a particular composite dye, consisting of π-conjugated indoline-rhodanine with a chlorophyll derivative, which induced panchromatic absorption in the visible range, efficient electron transfer, and prolonged stability [65]; a series of dyes with triphenylamine donor, vinyltiophene bridge, and a cationic pyridinium acceptor (cationic D-π-A photosensitizers) [66]. A superior H 2 evolution rate was recently reached with a thioalkyl-substituted tetrathiafulvalene dye on mesoporous TiO 2 [67].…”