Development of the sensitizer for generating higher-energy photons under diluted condition via the triplet-triplet annihilation-supported upconversion

Article abstract of DOI:10.1016/j.dyepig.2019.107821

It was previously reported that photon upconversion can occur in the solution containing anthracene and the Pt complex of octaethylporphyrin (PtOEP) via the triplet-triplet annihilation process. In this study, by employing the modified Pt complex of the dual anthracene-tethered porphyrin, DA-PtP as a sensitizer, it is demonstrated that shorter-wavelength light can be generated under diluted condition. We synthesized DA-PtP and compared upconversion properties by changing the type of sensitizers. Accordingly, it was shown that the photon upconversion proceeded with the xenon lamp (540 nm) in the presence of DA-PtP. Furthermore, it was found that the emission band in the shorter wavelength light in the near UV region was observed from the solution containing DA-PtP even under diluted condition. From the mechanistic investigation, it was proposed that the anthracene moieties in DA-PtP might inhibit to form agglomeration with the free anthracene. As a result, reabsorption of the higher-energy light generated from upconversion could be suppressed.

Full text of DOI:10.1016/j.dyepig.2019.107821

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Journal Pre-proof
Development of the sensitizer for generating higher-energy photons under diluted
condition via the triplet-triplet annihilation-supported upconversion
Kazuo Tanaka, Wataru Ohashi, Kenichi Inafuku, Shohei Shiotsu, Yoshiki Chujo
PII:
S0143-7208(19)31709-7
DOI:
https://doi.org/10.1016/j.dyepig.2019.107821
DYPI 107821
Reference:
To appear in: Dyes and Pigments
Received Date: 20 July 2019
Revised Date: 16 August 2019
Accepted Date: 16 August 2019
Please cite this article as: Tanaka K, Ohashi W, Inafuku K, Shiotsu S, Chujo Y, Development of the
sensitizer for generating higher-energy photons under diluted condition via the triplet-triplet annihilation-
supported upconversion, Dyes and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2019.107821.
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Development of the Sensitizer for Generating Higher-
Energy Photons under Diluted Condition via the Triplet-
Triplet Annihilation-Supported Upconversion
Kazuo Tanaka,* Wataru Ohashi, Kenichi Inafuku, Shohei Shiotsu, Yoshiki Chujo
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Katsura, Nishikyo-ku, Kyoto 615-8510, Japan
E-mail: tanaka@poly.synchem.kyoto-u.ac.jp
Phone: +81-75-383-2604
Fax: +81-75-383-2605
KEY WORDS: upconversion, triplet-triplet annihilation, sensitizer
1

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ABSTRACT
It was previously reported that photon upconversion can occur in the solution containing anthracene
and the Pt complex of octaethylporphyrin (PtOEP) via the triplet-triplet annihilation process. In this
study, by employing the modified Pt complex of the dual anthracene-tethered porphyrin, DA-PtP as a
sensitizer, it is demonstrated that shorter-wavelength light can be generated under diluted condition. We
synthesized DA-PtP and compared upconversion properties by changing the type of sensitizers.
Accordingly, it was shown that the photon upconversion proceeded with the xenon lamp (540 nm) in the
presence of DA-PtP. Furthermore, it was found that the emission band in the shorter wavelength light in
the near UV region was observed from the solution containing DA-PtP even under diluted condition.
From the mechanistic investigation, it was proposed that the anthracene moieties in DA-PtP might
inhibit to form agglomeration with the free anthracene. As a result, reabsorption of the higher-energy
light generated from upconversion could be suppressed.
2

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INTRODUCTION
The developments of new photo-cleavable functional groups and photoactivated prodrugs are of
significance in photo-medical treatments.1‒3 However, intrinsic low permeability of the light near 400
nm in the vital body is still the critical limitation on the application of activation to these photo-
responsive drugs at the deep spot inside bodies. One of potential strategies for overcoming this problem
is to combine the photon upconversion, in which the lower-energy incident light can be converted to the
higher-energy light.4,5 In ideal, by co-adding the photoactivated prodrugs with the anti-Stokes materials
which can cause upconversion, the permeable lower-energy light can be used for the activation of the
photoactivated prodrugs without significant decay of the incident light and damages to the bodies. Thus,
the photon upconversion is promised to be a key technology for extending the applicability of the
photomedical treatments.
When two triplet-excited molecules encounters, the one singlet-excited molecule can be generated
from two triplet-excited molecules. This phenomenon is called as triplet-triplet annihilation (TTA,
Scheme 1).6‒9 By selecting the types of sensitizers and emitters, the wavelengths of the acceptable
incident and the generated light can be tuned.6‒9 Indeed, TTA-supported upconversion systems have
been applied for in vivo imaging.10‒16 In particular, since UV light, which is favourable for inducing
photo-activation into prodrugs, can be generated, TTA-supported upconversion is regarded as a
promising tool for realizing phototherapy inside bodies.17‒20 However, another critical issue must be
considered under biological conditions. In our previous reports, the related molecules were loaded onto
the dendrimers having the silica element-block21,22 for facilitating efficient energy transferring and
TTA.23,24 It is likely that the local concentrations of sensitizers and fluorophores would decrease due to
diffusion, while the upconversion efficiency strongly depends on the concentration of the triplet-excited
molecules. To overcome this problem, the new system should be required for obtaining higher
efficiency even under diluted conditions.
3