Excited State Dynamics of Phthalocyanine Films

Gulbinas, Vidmantas; Chachisvilis, Mirianas; Valkūnas, Leonas; Sundström, Villy

doi:10.1021/jp951910j

Cited by 97 publications

(109 citation statements)

References 17 publications

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“…[25] We note that we observe timeindependent annihilation, which suggests three-dimensional diffusion. Our value for the annihilation rate constant is lower than the 2.3 Â 10 À8 cm 3 s À1 reported by Dicker et al [23] from time-resolved microwave conductivity measurements.…”

Section: (2)mentioning

confidence: 57%

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

2008

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Polymer solar cells are a promising technology for future power generation. In particular the polymer poly (3-hexylthiophene) (P3HT) has attracted widespread interest with power conversion efficiencies close to 5%. [1][2][3][4] Such devices employ the bulk heterojunction device structure, where the polymer is blended with a strong charge acceptor such as a fullerene. The processing of the blend affects its morphology and the formation of domains of P3HT-rich and fullerene-rich regions. It is at the interface between these two domains that excitons are dissociated into their constituent charges, a critical step in the operation of a solar cell. Excitons are only able to diffuse a short distance during their lifetime and therefore the size of the domains should ideally be on the order of the diffusion length, maximising the number of excitons reaching the interface and undergoing dissociation. The development of accurate measurements of the exciton diffusion length is therefore important for organic photovoltaics and the optimisation of materials, processing and device structure. To date there has been a wide range of reported values for different materials obtained by techniques such as surface quenching, [5][6][7][8] volume quenching, [9,10] microwave conductivity, [11] exciton-exciton annihilation [12,13] and photocurrent modelling of solar cells. [14] Of these the surface quenching technique is probably the most used, where the organic material is deposited onto a suitable quencher, resulting in a loss of luminescence. This loss can be quantified by comparing the emission from the quenched film with that of an identical film on a non-quenching substrate and will depend on the diffusion coefficient and the thickness of the organic film. This experiment can be performed via steady-state or time-resolved with most employing the former. However, a problem in steady-state measurements is that interference effects in the layer structures used can strongly modify the amount of light absorbed. [7] Time-resolved techniques do not require absolute measurements of the luminescence as it is only the decay of the emission from the material that is actually needed, though the initial excitation profile is influenced by optical interference. Exciton diffusion in polymers occurs on a time range from 1 ps to $1 ns, [15] thus any measurements should aim to cover this range. In this communication we will describe how time-resolved measurements of fluorescence, coupled with an appropriate quencher, enable robust measurements of the diffusion coefficient. We have applied this technique to the polymer P3HT, which despite being the most used polymer in organic photovoltaic research, has had little published on its exciton diffusion. Kroeze et al.[11] reported a value for the diffusion length of 2.6-5.3 nm from time-resolved microwave conductivity measurements, depending on whether or not excitons were reflected at the polymer/air interface. Using oxygen-induced fluorescence quenching in P3HT, Lü er et al. [9] obtained a minimum value...

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Section: (2)mentioning

confidence: 57%

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

2008

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“…[50][51][52][53][54][55][56][57][58][59][60][61]64 It is noteworthy that the coating thickness of the ZnPc aggregates varies between 5 and 10 nm on the surface of the TiO 2 /ZnPc nanocomposite, 30 suggesting a remote possibility of occurrence of ZnPc in the monomeric form in this material.…”

Section: 63mentioning

confidence: 99%

“…[50][51][52][53] When associated with bulk TiO 2 , the electron transfer from excitons of metal phthalocyanine aggregates to the oxide surface has been reported as a preferential way, [54][55][56] PCT: paracetamol; k min : apparent rate constant for PCT mineralization. (28) However, due to its short lifetime in solution, it has been reported that the contribution of 1 O 2 in photocatalytic reactions is limited in most cases.…”

Section: Control Experimentsmentioning

confidence: 99%

“…Similarly, a decrease of performance of about 12% was verified in the reactions using TiO 2 -P25 at pH 10.0 with addition of H 2 O 2 , and only of 5% when the nanocomposite was used. The different behaviors should be related to differences in the reaction chains triggered by these photocatalysts.It is well known that the relaxation of excited states in aggregates of metal phthalocyanines is predominantly due to very fast thermal deactivation processes, committing the occurrence of other processes, such as the intersystem crossing.50-53 When associated with bulk TiO 2 , the electron transfer from excitons of metal phthalocyanine aggregates to the oxide surface has been reported as a preferential way, [54][55][56] PCT: paracetamol; k min : apparent rate constant for PCT mineralization. …”

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confidence: 99%

“…50-53 When associated with bulk TiO 2 , the electron transfer from excitons of metal phthalocyanine aggregates to the oxide surface has been reported as a preferential way, [54][55][56] PCT: paracetamol; k min : apparent rate constant for PCT mineralization. …”

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Efficient Mineralization of Paracetamol Using the Nanocomposite TiO₂/Zn(II) Phthalocyanine as Photocatalyst

França¹,

Santos²,

Silva³

et al. 2016

Journal of the Brazilian Chemical Society

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The photocatalytic performance of a composite based on the association of TiO 2 and 2.5 wt.% of zinc(II) phthalocyanine (TiO 2 /ZnPc) was evaluated towards the mineralization of paracetamol and compared to that observed for the bare oxide in different pH and H 2 O 2 concentrations. The results show that the photocatalytic performances were influenced by the pH, with maximum efficiency around the isoelectric point. Mineralization efficiencies between 86-91% was obtained using TiO 2 /ZnPc in pH 5.5-6.8, with 33 mg L -1 of H 2 O 2 , ca. 15% higher than that observed with TiO 2 . The mineralization efficiencies using bare TiO 2 and TiO 2 /ZnPc were respectively 112 and 18% lower in the absence of H 2 O 2 . The better performance of TiO 2 /ZnPc is related to its extended light absorption and non-uniform coating of the TiO 2 surface by ZnPc aggregates. Above pH 6.8, the mineralization efficiencies decrease for both photocatalysts, although the consumption of H 2 O 2 remains above 90%, due to its decomposition in alkaline pH.Keywords: mineralization, paracetamol, heterogeneous photocatalysis, role of pH and hydrogen peroxide, TiO 2 /zinc(II) phthalocyanine nanocomposite IntroductionSince initial studies by Fujishima and Honda, 1 heterogeneous photocatalysis 2 has attracted considerable attention due to its many technological applications, such as H 2 production, 3-5 CO 2 reduction, 6-8 environmental remediation, 9-12 among others. TiO 2 has been widely used in heterogeneous photocatalysis due its low cost, low toxicity, chemical and photochemical stability, usually expressive photocatalytic activity and versatility. 2,10,12,13 Its main limitation as photocatalyst is related to the lack of absorption in the visible region, which limits its use under solar irradiation. Several strategies have been employed to overcome this limitation, including doping 3 and production of nanocomposites. 9,[12][13][14] TiO 2 -based photocatalysis has been specially used in environmental remediation for the removal of recalcitrant and hazardous organic pollutants in wastewater. 9,15 The radicals produced from its excitation by light are able to efficiently oxidize organic pollutants leading in some cases to a complete mineralization of the organic matter.Paracetamol (N-acetyl-p-aminophenol, PCT), Figure 1a, among other pharmaceutical products, their metabolites, pesticides, hormones and herbicides, 9,16-20 is calling attention due to its persistence in the environment and the inability of the sewage treatment plants in removing this contaminant, which may result in bioaccumulation and harmful consequences for ecosystems. 17,[20][21][22] Although PCT is metabolized mainly by the liver, up to 68% of this drug tends to be excreted in the urine when ingested within permitted levels. [21][22][23][24] It should be emphasized that one of the routes of paracetamol metabolism produces highly toxic metabolites able to bind covalently to cysteine present in proteins. 23,25Figure 1. Chemical structure of PCT (a) and Zn(II) phthalocyanine (b). França e...

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Exciton–Exciton Annihilation in Mixed‐Phase Polyfluorene Films

Shaw

Ruseckas

Peet

et al. 2009

Adv Funct Materials

105

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Singlet–singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of β‐phase chains using time‐resolved fluorescence. On a timescale of >15 ps after excitation, the results are fitted well by a time‐independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time‐dependent annihilation rate is observed during the first 15 ps in the glassy phase and in the β‐phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low‐energy sites. The annihilation rate in the mixed‐phase films increases with increasing fraction of β‐phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersedβ‐phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line‐dipole approximation for an exciton wavefunction extending over 2.5 nm. The results indicate that glassy andβ‐phase chromophores are intimately mixed rather than clustered or phase‐separated.

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Excited State Dynamics of Phthalocyanine Films

Cited by 97 publications

References 17 publications

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

Efficient Mineralization of Paracetamol Using the Nanocomposite TiO₂/Zn(II) Phthalocyanine as Photocatalyst

Exciton–Exciton Annihilation in Mixed‐Phase Polyfluorene Films

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Excited State Dynamics of Phthalocyanine Films

Cited by 97 publications

References 17 publications

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

Exciton Diffusion Measurements in Poly(3‐hexylthiophene)

Efficient Mineralization of Paracetamol Using the Nanocomposite TiO2/Zn(II) Phthalocyanine as Photocatalyst

Exciton–Exciton Annihilation in Mixed‐Phase Polyfluorene Films

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Efficient Mineralization of Paracetamol Using the Nanocomposite TiO₂/Zn(II) Phthalocyanine as Photocatalyst