Effect of Conjugation Length on Photoinduced Charge Transfer in π‑Conjugated Oligomer-Acceptor Dyads

A series of π-conjugated oligomer-acceptor dyads were synthesized that feature oligo­(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PE<i>n</i>-NDI, where <i>n</i> = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE → NDI charge transfer dominates the deactivation of excited states of the PE<i>n</i>-NDI oligomers. Both charge separation (CS) and charge recombination (CR) are strongly exothermic (Δ<i>G</i>⁰_CS ∼ −1.1 and Δ<i>G</i>⁰_CR ∼ −2.0 eV), and the driving forces do not vary much across the series because the oxidation and reduction potentials and singlet energies of the OPEs do not vary much with their length. Bimolecular photoinduced charge transfer between model OPEs that do not contain the NDI acceptors with methyl viologen was studied, and the results reveal that the absorption of the cation radical state (OPE^+•) remains approximately constant (λ ∼ 575 nm) regardless of oligomer length. This finding suggests that the cation radical (polaron) of the OPE is relatively localized, effectively occupying a confined segment of <i>n</i> ≤ 4 repeat units in the longer oligomers. Photoinduced intramolecular electron transfer dynamics in the PE<i>n</i>-NDI series was investigated by UV–visible femtosecond transient absorption spectroscopy with visible and mid-infrared probes. Charge separation occurs on the 1–10 ps time scale with the rates decreasing slightly with increased oligomer length (β_CS ∼ 0.15 Å^–1). The rate for charge-recombination decreases in the sequence PE4-NDI > PE6-NDI ∼ PE8-NDI. The discontinuous distance dependence in the rate for charge recombination may be related to the spatial localization of the positive polaron state in the longer oligomers

Data_Sheet_2_Association between white matter alterations and domain-specific cognitive impairment in cerebral small vessel disease: A meta-analysis of diffusion tensor imaging.DOC

ObjectiveTo investigate the association between diffusion tensor imaging (DTI) findings and domain-specific cognitive impairment in cerebral small vessel disease (CSVD).MethodsDatabases such as PubMed, Excerpta Medical Database (EMBASE), Web of Science, Cochrane Library, Chinese National Knowledge Infrastructure Databases (CNKI), Wanfang, Chinese Biomedical Literature Database (SinoMed), and Chongqing Chinese Science and Technology Periodical Database (VIP) were comprehensively retrieved for studies that reported correlation coefficients between cognition and DTI values. Random effects models and meta-regression were applied to account for heterogeneity among study results. Subgroup and publication bias analyses were performed using Stata software.ResultsSeventy-seven studies involving 6,558 participants were included in our meta-analysis. The diagnosis classification included CSVD, white matter hyperintensities (WMH), subcortical ischemic vascular disease, cerebral microbleeding, cerebral amyloid angiopathy (CAA), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and Fabry disease. The pooled estimates showed that the fractional anisotropy (FA)-overall exhibited a moderate correlation with general cognition, executive function, attention, construction, and motor performance (r = 0.451, 0.339, 0.410, and 0.319), and the mean diffusitivity/apparent diffusion coefficient (MD/ADC)-overall was moderately associated with general cognition, executive function, and memory (r = −0.388, −0.332, and −0.303, respectively; ps ConclusionLower FA or higher MD/ADC values were related to more severe cognitive impairment. General cognition and executive function domains attracted the greatest interest. The FL was commonly examined and strongly associated with general cognition, executive function, and attention. The CC was strongly associated with memory and attention. The CG was strongly related to general cognition and attention. The CR, IC, and TR were also strongly related to general cognition. Indeed, these results should be validated in high-quality prospective studies with larger sample sizes.Systematic review registrationhttp://www.crd.york.ac.uk/PROSPERO, identifier: CRD42021226133.</p

Data_Sheet_1_Association between white matter alterations and domain-specific cognitive impairment in cerebral small vessel disease: A meta-analysis of diffusion tensor imaging.DOCX

ObjectiveTo investigate the association between diffusion tensor imaging (DTI) findings and domain-specific cognitive impairment in cerebral small vessel disease (CSVD).MethodsDatabases such as PubMed, Excerpta Medical Database (EMBASE), Web of Science, Cochrane Library, Chinese National Knowledge Infrastructure Databases (CNKI), Wanfang, Chinese Biomedical Literature Database (SinoMed), and Chongqing Chinese Science and Technology Periodical Database (VIP) were comprehensively retrieved for studies that reported correlation coefficients between cognition and DTI values. Random effects models and meta-regression were applied to account for heterogeneity among study results. Subgroup and publication bias analyses were performed using Stata software.ResultsSeventy-seven studies involving 6,558 participants were included in our meta-analysis. The diagnosis classification included CSVD, white matter hyperintensities (WMH), subcortical ischemic vascular disease, cerebral microbleeding, cerebral amyloid angiopathy (CAA), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and Fabry disease. The pooled estimates showed that the fractional anisotropy (FA)-overall exhibited a moderate correlation with general cognition, executive function, attention, construction, and motor performance (r = 0.451, 0.339, 0.410, and 0.319), and the mean diffusitivity/apparent diffusion coefficient (MD/ADC)-overall was moderately associated with general cognition, executive function, and memory (r = −0.388, −0.332, and −0.303, respectively; ps ConclusionLower FA or higher MD/ADC values were related to more severe cognitive impairment. General cognition and executive function domains attracted the greatest interest. The FL was commonly examined and strongly associated with general cognition, executive function, and attention. The CC was strongly associated with memory and attention. The CG was strongly related to general cognition and attention. The CR, IC, and TR were also strongly related to general cognition. Indeed, these results should be validated in high-quality prospective studies with larger sample sizes.Systematic review registrationhttp://www.crd.york.ac.uk/PROSPERO, identifier: CRD42021226133.</p

Table_1_Association between white matter alterations and domain-specific cognitive impairment in cerebral small vessel disease: A meta-analysis of diffusion tensor imaging.docx

ObjectiveTo investigate the association between diffusion tensor imaging (DTI) findings and domain-specific cognitive impairment in cerebral small vessel disease (CSVD).MethodsDatabases such as PubMed, Excerpta Medical Database (EMBASE), Web of Science, Cochrane Library, Chinese National Knowledge Infrastructure Databases (CNKI), Wanfang, Chinese Biomedical Literature Database (SinoMed), and Chongqing Chinese Science and Technology Periodical Database (VIP) were comprehensively retrieved for studies that reported correlation coefficients between cognition and DTI values. Random effects models and meta-regression were applied to account for heterogeneity among study results. Subgroup and publication bias analyses were performed using Stata software.ResultsSeventy-seven studies involving 6,558 participants were included in our meta-analysis. The diagnosis classification included CSVD, white matter hyperintensities (WMH), subcortical ischemic vascular disease, cerebral microbleeding, cerebral amyloid angiopathy (CAA), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and Fabry disease. The pooled estimates showed that the fractional anisotropy (FA)-overall exhibited a moderate correlation with general cognition, executive function, attention, construction, and motor performance (r = 0.451, 0.339, 0.410, and 0.319), and the mean diffusitivity/apparent diffusion coefficient (MD/ADC)-overall was moderately associated with general cognition, executive function, and memory (r = −0.388, −0.332, and −0.303, respectively; ps ConclusionLower FA or higher MD/ADC values were related to more severe cognitive impairment. General cognition and executive function domains attracted the greatest interest. The FL was commonly examined and strongly associated with general cognition, executive function, and attention. The CC was strongly associated with memory and attention. The CG was strongly related to general cognition and attention. The CR, IC, and TR were also strongly related to general cognition. Indeed, these results should be validated in high-quality prospective studies with larger sample sizes.Systematic review registrationhttp://www.crd.york.ac.uk/PROSPERO, identifier: CRD42021226133.</p

Table_2_Association between white matter alterations and domain-specific cognitive impairment in cerebral small vessel disease: A meta-analysis of diffusion tensor imaging.docx

ObjectiveTo investigate the association between diffusion tensor imaging (DTI) findings and domain-specific cognitive impairment in cerebral small vessel disease (CSVD).MethodsDatabases such as PubMed, Excerpta Medical Database (EMBASE), Web of Science, Cochrane Library, Chinese National Knowledge Infrastructure Databases (CNKI), Wanfang, Chinese Biomedical Literature Database (SinoMed), and Chongqing Chinese Science and Technology Periodical Database (VIP) were comprehensively retrieved for studies that reported correlation coefficients between cognition and DTI values. Random effects models and meta-regression were applied to account for heterogeneity among study results. Subgroup and publication bias analyses were performed using Stata software.ResultsSeventy-seven studies involving 6,558 participants were included in our meta-analysis. The diagnosis classification included CSVD, white matter hyperintensities (WMH), subcortical ischemic vascular disease, cerebral microbleeding, cerebral amyloid angiopathy (CAA), cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and Fabry disease. The pooled estimates showed that the fractional anisotropy (FA)-overall exhibited a moderate correlation with general cognition, executive function, attention, construction, and motor performance (r = 0.451, 0.339, 0.410, and 0.319), and the mean diffusitivity/apparent diffusion coefficient (MD/ADC)-overall was moderately associated with general cognition, executive function, and memory (r = −0.388, −0.332, and −0.303, respectively; ps ConclusionLower FA or higher MD/ADC values were related to more severe cognitive impairment. General cognition and executive function domains attracted the greatest interest. The FL was commonly examined and strongly associated with general cognition, executive function, and attention. The CC was strongly associated with memory and attention. The CG was strongly related to general cognition and attention. The CR, IC, and TR were also strongly related to general cognition. Indeed, these results should be validated in high-quality prospective studies with larger sample sizes.Systematic review registrationhttp://www.crd.york.ac.uk/PROSPERO, identifier: CRD42021226133.</p

Polymer Chromophore-Catalyst Assembly for Solar Fuel Generation

A polystyrene-based chromophore-catalyst assembly (poly-<b>2</b>) has been synthesized and assembled at a mesoporous metal oxide photoanode. The assembly contains water oxidation catalyst centers based on [Ru­(trpy) (phenq)]²⁺ (Ru-Cat) and [Ru­(bpy)₃]²⁺ derivatives (Ru-C) as chromophores (trpy= 2,2′;6,2″- terpyridine, phenq = 2-(quinol-8′-yl)-1,10-phenanthroline and bpy = 2,2′-bipyridine). The photophysical and electrochemical properties of the polychromophore-oxidation catalyst assembly were investigated in solution and at the surface of mesoporous metal oxide films. The layer-by-layer (LbL) method was utilized to construct multilayer films with cationic poly-<b>2</b> and anionic poly­(acrylic acid) (PAA) for light-driven photochemical oxidations. Photocurrent measurements of (PAA/poly-<b>2</b>)₁₀ LbL films on mesoporous TiO₂ demonstrate light-driven oxidation of phenol and benzyl alcohol in aqueous solution. Interestingly, illumination of (PAA/poly-<b>2</b>)₅ LbL films on a fluorine doped SnO₂/TiO₂ core/shell photoanode in aqueous solution gives rise to an initial photocurrent (∼18.5 μA·cm^–2) that is in part ascribed to light driven water oxidation

Light Harvesting and Charge Separation in a π‑Conjugated Antenna Polymer Bound to TiO₂

This paper describes the photophysical and photoelectrochemical characterization of a light harvesting polychromophore array featuring a polyfluorene backbone with covalently attached Ru­(II) polypyridyl complexes (PF-Ru-A), adsorbed on the surface of mesostructured TiO₂ (PF-Ru-A//TiO₂). The surface adsorbed polymer is characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, providing evidence for the morphology of the surface adsorbed polymer and the mode of binding. Photoexcitation of the Ru­(II) complexes bound to the metal oxide surface (proximal) results in electron injection into the conduction band of TiO₂, which is then followed by ultrafast hole transfer to the polymer to form oxidized polyfluorene (PF⁺). More interestingly, chromophores that are not directly bound to the TiO₂ interface (distal) that are excited participate in site-to-site energy transfer processes that transport the excited state to surface bound chromophores where charge injection occurs, underscoring the antenna-like nature of the polymer assembly. The charge separated state is long-lived and persists for >100 μs, a consequence of the increased separation between the hole and injected electron