Novel visible-light-driven photocatalyst. Poly(p-phenylene)-catalyzed photoreductions of water, carbonyl compounds, and olefins

Abstract

The insoluble yellow powder of poly(p-phenylene) (PPP) prepared by nickel-catalyzed polycondensation of the Grignard reagent from 1,4-dibromobenzene shows photocatalytic activity under visible light toward water, carbonyl compounds, and olefins. Water is photoreduced to H2 in the presence of amines as sacrificial electron donors. The H2 evolution is enhanced 3-20 times by noble-metal deposition, in which Ru deposition is the most effective. Apparent quantum yields (4>('/2H2)) for Ru-loaded PPP-catalyzed H2 evolution depend on the irradiation wavelength, reaching a maximum value of 0.015 at 405 nm. On the other hand, nonmetallized PPP can more efficiently photocatalyze the reduction of carbonyls and electron-deficient olefins by triethylamine in methanol compared to Ru-loaded PPP, in cases where the reduction potentials of the substrates are more positive than -2.0 V vs Ag/0.01 M AgNO}. The carbonyls are reduced to the corresponding alcohols and/or pinacols, whereas the reduction of the olefins to the dihydro compounds is accompanied by rapid cis-trans photoisomerization. From the deuterium incorporation experiments for the photocatalyzed reduction of methyl 4-cyanocinnamate, 6j, in methanol-O-rf, disproportionation of one-electron-transfer reduction intermediates is suggested to be responsible for the eventual two-electron reductions and the cis-trans photoisomerization. The physical and spectral properties of PPP's are characterized, and the mechanism is discussed in terms of the energy structure.Since the photolysis of water on a Ti02 electrode (Honda-Fujishima effect) was reported,1 photoinduced charge separation on inorganic semiconductors has been widely investigated as a key step in the conversion of light to chemical potential energy.1 2 In order to achieve high efficiency in photochemical conversion or to utilize visible light much more effectively, integrated chemical systems using semiconductor/redox couple interfaces combined with metallic cocatalysts, electron relays, sensitizers, or polymers have been extensively studied.2'3 On the other hand, since polyacetylene film was synthesized and chemical doping effects on electric conductivity were discovered,4 a number of organic polymers with conjugated welectrons have been synthesized and some novel applications such as electrochromic polymers,5 organic batteries,6 sensing polymers,7 and solar batteries8 have been successfully proposed. Conjugated polymers called conducting polymers show electrical conductivity only when they are doped chemically with either electron donors or acceptors. Under undoped conditions, however, they are semiconducting and should be called polymeric organic semiconductors.9 Among such 7r-bond conjugated polymers, poly(pphenylene) (PPP) polymers are resistant to oxidation, thermal degradation, and radiation under aerobic conditions10 and are reported to have band gaps in the visible-light region.11 Evolution

Self‐Assembled PDINH Supramolecular System for Photocatalysis under Visible Light

“…Hence, organocatalysts have attracted the interests of many researchers during the last decades. However, organocatalysts have mainly been based on two types of organic materials: organometallic complexes, [1] in which the metallic composition may limit their practical applications due to high cost, potential toxicity, and poor sustainability; or covalent organic polymers, including commonly reported carbon nitride, [2,3] triazine/hydrazone-based carbon nitrides, [4][5][6][7] and some covalent organic polymers based on poly(p-phenylene), [8,9] poly(phenyleneethinylene), [10] poly(diph enylbutadiyne), [11] poly(azomethine), [12] and carbazolic frameworks. [13] However, non-covalent self-assembly supramolecular systems composed of purely organic molecules alone, working as a photocatalyst with wide visible-light responses has not been reported.…”

Photocatalytic H2 Evolution by Pt-Loaded 9,9′-Spirobifluorene-Based Conjugated Microporous Polymers under Visible-Light Irradiation

“…Hydrogen evolution was detected in the manner described above. 6 . After 20 h, 4.0¯mol (1.0 wt % Pt), 9.3¯mol (4.6 wt % Pt), and 2.5¯mol (10 wt % Pt) of H 2 were produced.…”

“…5 The high thermal and photochemical stability of these materials is also useful for particular applications. Various CMPs have been applied in photocatalytic hydrogen evolution from water, including poly( pphenylene), 6 poly(phenyleneethynylene), 5 poly(azomethine), 7 triphenylaminebiphenyl polymers, 8 and pyrenebenzene polymers. 9 Carbon nitride CMPs also facilitate efficient photoinduced hydrogen evolution from water.…”

“…An energy diagram constructed from diffuse reflectance and photoelectron spectra indicated that the LUMO for COP-3 was located at a potential energy that was higher than the reduction potential for PtCl 6 2¹ and H + , and the HOMO for COP-3 was located at a potential that was more negative than the oxidation potential for TEOA and H 2 O. The superior catalytic performance of Pt/COP-3 compared to a physical mixture of COP-3/MV 2+ /Pt-PAA suggests that direct fixation of Pt nanoparticles on COP-3 is favorable for efficient electron transfer from COP-3 to the Pt catalyst.…”

Fluorescein supramolecular nanosheets: A novel organic photocatalyst for visible-light-driven H2 evolution from water

“…Metal-free photocatalysts, usually containing low cost and earth-abundant C, N and O elements, are more advantageous than the traditional metal-based photocatalysts and have attracted considerable interest for many years [5][6][7][8][9][10]. In the reported metal-free photocatalysts, polymer carbon nitride (PCN) is extensively studied, but the relatively large band gap (~2.7 eV) and the low activity limit its photocatalytic applications [11][12][13][14][15][16][17].…”