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Article

S/Se-Terchalcogenophene-C60 Dyads: Synthesis and Characterization of Optical and Photosensitizing Properties

by
Radosław Motyka
1,2,*,
Klaudia Nastula
1,
Piotr Pander
1,3,4,
Damian Honisz
1,
Mateusz Tomczyk
1,
Karol Erfurt
1 and
Agata Blacha-Grzechnik
1,3,*
1
Faculty of Chemistry, Silesian University of Technology, Strzody 9, 44-100 Gliwice, Poland
2
Centre of Polymer and Carbon Materials, Polish Academy of Sciences, Curie-Sklodowskiej 34, 41-819 Zabrze, Poland
3
Centre for Organic and Nanohybrid Electronics, Silesian University of Technology, Konarskiego 22B, 44-100 Gliwice, Poland
4
Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
*
Authors to whom correspondence should be addressed.
Materials 2023, 16(7), 2605; https://doi.org/10.3390/ma16072605
Submission received: 27 February 2023 / Revised: 13 March 2023 / Accepted: 21 March 2023 / Published: 24 March 2023
Browse Figures
Versions Notes

Abstract

:
Fullerenes have been long investigated for application as singlet oxygen sources. Even though they possess high photosensitizing efficiency, their practical use is still limited, mostly because of insufficient absorption of visible and/or near-infrared light. This limitation can be overcome by introducing organic chromophores that absorb longer-wavelength light, either by covalent attachment to C60 or by its encapsulation in a polymeric matrix. In this work, we investigated the photosensitizing properties of the C60 molecule functionalized with organic units comprising thiophene or selenophene rings. The chemical structures of the synthesized dyads were characterized by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. The influence of the S/Se atoms and vinyl linkage between the organic unit and C60 on the absorptive and emissive properties of the dyads was investigated and correlated with their photosensitizing activity. For the latter, we used a standard chemical singlet oxygen trap. A selected dyad C60ThSe2 was also applied as a source of singlet oxygen in a model photocatalyzed synthesis of the fine chemical juglone from 1,5-dihydroxynapthalene.

1. Introduction

Singlet oxygen (1O2) plays an important role in many biological and chemical processes owing to its highly oxidative properties and high reactivity. It was first observed in the 1960s and remains within the area of interest of scientists as a useful reagent in oxidation processes, in fine chemical synthesis, or in medicine, e.g., photodynamic therapy (PDT) [1,2,3,4]. 1O2, a form of reactive oxygen species (ROS), can be formed in various (photo)chemical and physical processes. Among these processes, photosensitization is considered the most favorable example. This process relies on the presence of three components: (1) a photoactive molecule, i.e., a photosensitizer (PS); (2) molecular oxygen; and (3) light of a suitable wavelength to be absorbed by the PS. In simple terms, the light-activated production of 1O2 undergoes three major steps: (i) absorption of light by the PS to form an excited singlet state (1PS*); (ii) formation of a triplet excited state of the PS (3PS*) by intersystem crossing (ISC); and (iii) Dexter electron transfer from the 3PS* to triplet oxygen, yielding singlet oxygen [4]. Even though several groups of organic photosensitizers have been investigated, such as porphyrins, phthalocyanines, and other transition metal complexes [4], the search for the ideal PS molecule with high photostability and optimal optical and photosensitizing properties is ongoing.
Fullerene (C60) has attracted significant attention in the last years due to its good electron accepting/transporting properties, leading to its broad use in optoelectronic devices [5,6] or as a singlet oxygen source in photochemical processes [7,8,9,10]. Unsubstituted fullerene produces singlet oxygen with very high efficiency [11,12,13] but suffers from low absorption in the visible region of the electromagnetic spectrum and low solubility in organic solvents (while being insoluble in water [14]), which strongly hinders its practical use. It has been shown that both problems can be solved by appropriate functionalization of the fullerene unit [11,15,16,17,18,19]. A number of works have shown an enhancement in the optical and photosensitizing properties of fullerene-based photosensitizers. For example, several fullerene dyads, triads, and tetrads with visible to near-infrared light-absorbing groups have been reported [20,21,22,23,24,25,26,27]. However, due to the low solubility of C60, its functionalization is usually arduous, especially when introducing functional groups, which may lead to even lower solubility.
In our previous works on C60 dyads, we have shown that fullerene having only thiophene or selenophene substituents can be deposited as a layer in an electrochemical polymerization and can be effectively used as a heterogeneous source of singlet oxygen [28,29]. In this work, we aimed to investigate the optical and photosensitizing properties of those simple fullerene dyads, with three units of five-membered heterocycles serving as light-absorbing antennas. In contrast to our previous works dealing with the solid photoactive systems, we characterized the photoactivity of the C60 dyads in solution phase, investigating the effect of a heavier heterocyclic chalcogen and the presence of a vinyl spacer between the C60 unit and the antenna. Thus, three fullerenes with thiophene/selenophene side substituents were synthesized, and their structures were confirmed by means of nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. The optical properties were investigated in solution with UV–Vis absorption and fluorescence spectroscopy. The photosensitizing properties were investigated using an indirect method with a tetraphenylcyclopentadienone (TPCPD) 1O2 trap. The oxidation of 1,5-dihydroxynapthalene to juglone was used as a model homogenous photo-oxidation process to demonstrate the effectiveness of our dyads in generating singlet oxygen. Finally, we discussed the influence of the dyad structure on its optical and photosensitizing properties, demonstrating the significance of the ISC occurring directly on the antenna.

2. Materials and Methods

2.1. Materials

Thiophene– and selenophene–C60 dyads (Figure 1) were synthesized based on previously reported procedures [30,31,32,33]. The detailed synthetic route and the identification of the obtained products are shown in the Supporting Information. 2,2′:5′,2″-Terthiophene (TTh) and fullerene C60 were purchased from Alfa Aesar, Haverhill, MA, USA (purity 99%) and Sigma Aldrich, St. Louis, MO, USA (purity 98%), respectively. Dichloromethane (HPLC grade, Sigma Aldrich, St. Louis, MO, USA) was used as a solvent for UV–Vis spectroscopy and photophysical studies. Tetraphenylcyclopentadienone (TPCPD) (Acros Organics, Geel, Belgium, purity 99%) in dichloromethane was used as a specific 1O2 quencher. Perinaphthenone (Sigma Aldrich, St. Louis, MO, USA, purity 97%) was applied as a reference for the determination of the quantum yield of singlet oxygen production. Photooxidation of 1,5-dihydroxynaphtalene (DHN, Sigma Aldrich, St. Louis, MO, USA, purity 97%) was conducted in dichloromethane: methanol (Across Organics, Geel, Belgium, purity 99.9%) mixture (9:1 v/v).

2.2. Characterization of Optical and Photosensitizing Properties of Thiophene/Selenophene Dyads

UV–Vis spectra of fullerene dyads in dichloromethane were collected in a 2 mm quartz cuvette (Hellma Analytics, Müllheim, Germany) with a Hewlett Packard 8452A UV–Vis spectrometer. The concentration of dyads varied between 6.25•10−3 and 0.1 mM.
Photoluminescence (PL) spectra in solutions were recorded using a QePro compact spectrometer (Ocean Optics). Excitation curves were recorded using a Horiba Fluorolog fluorescence spectrometer. Time-resolved photoluminescence measurements in solution were recorded with a Horiba DeltaFlex TCSPC system using a 405 nm Delta Diode light source.
The photosensitizing properties of thiophene/selenophene dyads were investigated with an indirect method using UV-Vis spectroscopy with a 0.05 mM solution of tetraphenylcyclopentadienone (TPCPD) in dichloromethane [34] as a specific singlet oxygen trap. The concentration of photosensitizer was 0.025 mM. The progress of the reaction between TPCPD and 1O2 was monitored with UV-Vis spectrophotometry using the 510 nm absorption band of TPCPD as a reference. We used standard 10 mm × 4 mm quartz cuvettes (Hellma Analytics), and the experimental setup was arranged in such a way that the irradiation beam with a ca. 0.5 cm2 cross-section was perpendicular to the optical path of the UV-Vis spectrophotometer. 365 nm fiber-coupled LED (Thorlabs, Bergkirchen, Germany) or xenon lamp (Thorlabs) served as the excitation light source in the experiment. The UV-Vis spectra were acquired at time intervals in which clear changes in the absorbance of the chemical trap could be observed.
The quantum yield of singlet oxygen generation was estimated with a relative method using Equation (1), with perinaphthenone (PN) as a reference (ΦPN = 0.95 in dichloromethane) [35].
Φ i = Φ PN · m i m PN · α PN α i
where the indices i and PN indicate fullerene dyad and perinaphthenone, respectively; Φ is the quantum yield of singlet oxygen photosensitization; m is the slope of temporal change of absorbance at 510 nm of TPCPD; α is given by α = 1 − 10–A, where A is absorbance at 365 nm [36,37,38].
The selected fullerene dyads and unsubstituted C60 were used as sources of 1O2 in a model photooxidation reaction applicable for fine chemical synthesis, i.e., the oxidation of DHN. Firstly, in situ measurements were undertaken using the measurement setup described above with a 1 mM solution of DHN in CH2Cl2:CH3OH. The progress of the reaction was monitored by observing an increase in absorbance at 420 nm. Photo-oxidation of DHN was also performed on a laboratory scale using a photoreactor (100 mL of borosilicate glass flask) and a xenon lamp (Thorlabs) as a light source. All experiments were conducted on the freshly prepared solution of fullerene dyads.

3. Results and Discussion

3.1. Synthesis

All compounds were synthetized using 3-formylthiophene (1) as a starting material. The synthetic path is shown in Scheme 1.
In the first step, thiophene aldehyde (1) was brominated with the use of N-bromosuccynimide [30] to give product 2, which was coupled with 2-thienylboronic acid (6) in the Suzuki–Miyaura reaction [31] and with 2-tributylstannylselenophene (7) using the Stille reaction [32], which led to 2,2′:5′,2″-terthiophene-3′-carbaldehyde (3) and 2,5-di(selenophen-2-yl)thiophene-3-carbaldehyde (4). Compounds 3 and 4 were used to obtain the final dyads C60TTh and C60ThSe2 by reacting them with buckminsterfullerene and sarcosine (N-methylglycine) in the 2 + 3 dipolar cycloaddition (Prato reaction) [32]. C60TThVin was synthetized in a similar manner, but in the last step (Prato reaction), 3-[(2,2′:5′,2″-terthiophen)-3′-yl]acrylaldehyde (5) was used. Compound 5 was prepared from derivative 3 by the Wittig reaction with (1,3-dioxolan-2-ylmethyl)triphenylphosphonium bromide [33] and subsequent hydrolysis of the acetal group.

3.2. Characterization of Optical and Photosensitizing Properties of Thiophene/Selenophene Dyads

3.2.1. UV–Vis Absorption and Fluorescence Spectroscopy

Figure 2 (top) presents the normalized UV–Vis and PL spectra of the C60 dyads in CH2Cl2, and absorption spectra of the model C60 and TTh units. A summary of the photophysical properties of the dyads is presented in Table 1. The main absorption bands of the nonfunctionalized fullerene and terchalcogenophene-decorated C60 units are located within the 250–400 nm region and display a clear overlap. Weak absorption originating from the C60 extends out from 400 nm onward and beyond 600 nm. The absorption spectra of dyads are likely a superposition of the absorption originating from the two constituent units, with distinctive maxima at ~260 nm and ~330 nm originating from the C60 unit [11]. As the sharp absorption maxima characteristic for the C60 unit are retained in the decorated C60; therefore, it is likely the electronic structure of the fullerene unit is only weakly affected by functionalization. Therefore, the two constituent components of the dyads are electronically decoupled, hence behaving as isolated π systems. When excited with λexc = 365 nm, the dyads display weak photoluminescence characteristic of the C60 unit, with a maximum at 714 nm and a vibronic progression of ~1400 cm−1. The weak PL of the C60 dyads likely originates from the low luminescence yield of the C60 unit [39]. The weak PL in the ~400–500 nm region can be ascribed to the residual fluorescence of the antennas.
Precursors 3, 4, and 5, although structurally close to the respective dyad antennas, are suboptimal models for the systems, as demonstrated by the difference in PL spectra between 3 (a-TTh) and TTh (Figure 2 (middle)). However, they are still useful for explaining certain features of the luminescent behavior of the respective dyads. We note that the presence of a Se atom instead of a S atom has a minor effect on their photoluminescence spectrum, leading to a red shift by a few nanometers. On the contrary, the vinyl linker appears to have a profound effect on the PL spectra, which can be connected to extended conjugation by direct linkage to the central Th unit. The photoluminescence lifetime of the antennas is strongly linked to their structure—we observed the longest decay lifetime for 3 (τ = 1.8 ns) and a shorter lifetime of the analogue with a vinyl linker 5 (τ = 0.3 ns). The shortest lifetime is observed for 4 (τ = 0.1 ns) (Figure S1), which includes heavy Se atoms replacing some of the sulfur in the chalcogenophene rings. The direct reasons for the analogues with the vinyl linker showing shorter PL lifetimes than the nonvinyl dyads are unclear; however, the behavior of 4 is consistent with the heavy atom effect. In this case, the heavy Se atom induces faster rates of intersystem crossing, leading to fluorescence quenching and higher triplet populations originating from optically excited species.
A further investigation of the C60TTh dyad (Figure 2 (bottom)) confirms the tentative hypothesis of the role of the TTh antenna in the system. The excitation curve recorded with collection at 714 nm resembles the shape of the TTh absorption and does not display the C60 absorption peak at ~330 nm. This is crucial evidence for the role of the antenna in the absorption of light in the 300–400 nm region. Interestingly, the excitation curve displays a sharp maximum at ~430 nm, which can also be observed in the absorption spectra of C60TTh. C60 displays a similar sharp absorption peak at ~405 nm; therefore, we ascribe the ~430 nm band to the C60 unit—a redshift of this band with respect to C60 can be rationalized by a change in electronic structure resulting from functionalization. Hence, the C60 unit significantly contributes to the excitation curve from ~420 nm on. We observed similar behavior in the other dyads (Figure 3), with the ~430 nm C60 absorption band retained in all cases, confirming its origin from said unit. The maxima of the excitation curves display small shifts that correspond to the changes in the PL spectra of the respective model antennas in Figure 2 (middle), hence confirming their antenna-based origin.

3.2.2. Photosensitizing Properties of Dyads

From a wide range of possible singlet-oxygen-specific traps, we selected tetraphenylcyclopentadienone as the model quencher. This molecule is stable under white light illumination, can be used in dichloromethane, and—importantly—is selective toward 1O2 [34].
Figure 4 presents the UV–Vis spectra of TPCPD in CH2Cl2 recorded during the irradiation of C60TTh. A gradual decrease in the absorption band intensity at 510 nm indicates the reaction of TPCPD with singlet oxygen produced by the fullerene dyad C60ThSe2. Similar results were obtained with the other investigated dyads. The comparison (Figure 4 inset) shows that no drop in the TPCPD absorption band was recorded without the photosensitizer being present in the solution (blank), which demonstrates the stability of the TPCPD under illumination. The highest yield of TPCPD oxidation after 60 s was observed for C60ThSe2, while the lowest was observed for C60TTh. As reported earlier [40], TTh shows photosensitizing properties (Figure 4 inset); however, we observed a very low efficiency of singlet oxygen generation. As shown in Table 1, the introduction of a vinyl linker or replacement of two thiophene units with selenophene leads to an increase in the quantum efficiency of the photosensitization process.
The mechanism for singlet oxygen (1O2) generation by fullerene dyads suggested in the literature involves energy transfer from the photoexcited singlet states of the light-absorbing antennas (1A*) to the singlet state of the fullerene (1C60*), followed by intersystem crossing (ISC) to the triplet state of the C60 unit (3C60*), which is the final state responsible for generating 1O2 [11,20,41,42,43,44]. However, our results point at this mechanism not being the sole mode in which 1O2 is generated by our systems (Scheme 2). We noted that higher rates of intersystem crossing in the Se-containing dyads correlated with the largest ΦΔ values, which are inherently related to the final triplet populations localized on the C60 units (3C60*). This behavior suggests that the supportive mode for triplet generation in our systems is intersystem crossing from the 1A* to the 3A*, followed by triplet energy transfer to the 3C60*. Importantly, the C60 unit may also absorb light directly and produce 1O2 without the intermediary role of the antenna. The aforementioned mechanism suggested in the literature is still at play in our systems, as clearly demonstrated by the quenching of fluorescence from antennas by the C60 unit in Figure 2. We think that this proposed mechanism involving two distinct ISC pathways supplements those presented earlier in the literature. It is possible owing to the relatively fast ISC rates of selenophenes used as antennas. The popular BODIPY units used in related systems often display negligible ISC rates on their own, thus pointing at the ISC necessarily occurring outside of the BODIPY antenna unit and on the C60 moiety.

3.2.3. DHN Photooxidation

The oxidation of 1,5-dihydroxynaphtalene (DHN) to juglone (5-hydroxy-1,4-naphthoquinone), an anthelmintic drug, is classified as a fine chemical process that naturally occurs in plants, especially in black walnut [45,46]. We used this reaction as a model to demonstrate the photosensitizing properties of our fullerene dyads.
At first, we investigated the oxidation process in situ using the C60 dyads as a source of singlet oxygen and a xenon lamp as a light source. The progress of DHN oxidation can be monitored either as a decrease in the absorbance of DHN at 298 nm or as an increase in the absorbance of the absorption band of juglone at 420 nm [47,48]. Because the investigated dyads strongly absorb at ca. 300 nm, we chose the latter option as more reliable. Figure 4 presents a set of UV–Vis spectra of a DHN solution containing C60ThSe2 collected during irradiation. We observed that the absorbance of juglone at 420 nm gradually increased, indicating oxidation of DHN with singlet oxygen produced by the fullerene dyad. The comparison of C60ThSe2 with C60TTh and C60 (Figure 5 inset) indicated that the selenophene-containing dyad shows the highest efficiency of singlet oxygen generation, nearly two-fold higher than for the unsubstituted C60. The lower reaction yield with C60TTh than C60ThSe2 is in agreement with results obtained using TPCPD described above. This is mainly due to the higher ΦΔ owing to the heavy atom effect but also a slightly higher absorbance of C60ThSe2.
Finally, we used C60ThSe2 as the most effective singlet oxygen-generating agent for the synthesis of juglone on a preparative scale. For this purpose, 50 mL of a 25 mmol solution of DHN in a mixture of CH2Cl2:CH3OH (9:1 v/v) was placed in a 100 mL round-bottom borosilicate glass flask and was irradiated with a xenon lamp in the presence of 1% (by mass) of the photosensitizer and a constant flow of oxygen through the reaction mixture. The progress of the reaction was monitored by thin-layer chromatography using CH2Cl2 as the mobile phase and commercial juglone as a reference. The reaction was terminated after five hours when no increase in the amount of the target product was observed on the TLC plates. The product was isolated from the reaction mixture by column chromatography to give pure juglone (NMR spectra consistent with the commercial product) in a 40% yield. Although the yield achieved in this experiment was modest, it serves as a clear proof of concept for the use of our dyads for synthesis on a scale larger than micrograms.

4. Conclusions

In summary, fullerene dyads with organic units comprising three chalcogenophene rings were synthesized and their optical and photosensitizing properties characterized. It was shown that decoration with thiophene and selenophene units leads to a significant improvement in effective light absorption in the 300–420 nm region of the electromagnetic spectrum. All of the investigated C60 dyads exhibited photosensitizing properties, with the quantum efficiency of singlet oxygen generation being the highest for the selenium-containing dyad. They displayed near-infrared luminescence at 714 nm, characteristic of the C60 unit, indicating efficient energy transfer from the antenna to the fullerene despite the formal electronic decoupling of the two units. We suggest a two-pathway mechanism for the generation of triplet states at the C60 units: (1) singlet energy transfer from the antenna to the fullerene, with the ISC occurring on the latter; (2) triplet energy transfer from the antenna to the fullerene. The effect of the mechanism (2) is evident in the prominent oxygen-generating properties of C60ThSe2.
It was shown that modification of the fullerene dyad with only three thiophene units can increase the yield of DHN oxidation by ca. 30% and the subsequent exchange of sulfur by selenium atoms by a further ca. 70% with respect to undecorated C60. Thus, the reported dyads can be considered a cost-effective alternative to the previously reported photosensitizers based on fullerene dyads.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/ma16072605/s1, Synthesis and spectroscopic characterization of thiophene- and selenophene– C60 dyads. Figure S1. TCSPC traces in degassed CH2Cl2 solutions of 3, 4, and 5, c = 10−5 M. Collection wavelengths correspond to emission maxima in Figure 2 (middle).

Author Contributions

Conceptualization, A.B.-G. and R.M.; methodology, A.B.-G., R.M. and P.P.; validation, A.B.-G., R.M. and P.P.; formal analysis, A.B.-G., R.M., P.P. and D.H.; investigation, R.M., K.N., P.P., M.T., D.H. and K.E.; writing—original draft preparation, A.B.-G. and R.M.; writing—review and editing, A.B.-G., R.M. and P.P.; visualization, A.B.-G. and R.M.; supervision, A.B.-G.; project administration, A.B.-G.; funding acquisition, A.B.-G. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the National Science Center, Poland (grant number: 2016/21/D/ST5/01641). R.M. and D.H. acknowledge the EU’s Horizon 2020 for funding the OCTA project under grant agreement No. 778158. Research work was supported by the funds for science in 2018–2023 allocated to the implementation of an international cofinanced project by the Polish Ministry of Education and Science. ABG acknowledges Silesian University of Technology for the financial support provided under the Rector’s pro-quality grant No. 04/040/RGJ23/0239.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No data have been deposited.

Conflicts of Interest

The authors declare no conflict of interest.

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Materials 16 02605 g001 550
Figure 1. Investigated C60 dyads.
Figure 1. Investigated C60 dyads.
Materials 16 02605 g001
Materials 16 02605 sch001 550
Scheme 1. Synthetic path for investigated C60 dyads.
Scheme 1. Synthetic path for investigated C60 dyads.
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Materials 16 02605 g002 550
Figure 2. (top) Normalized UV–Vis absorption and photoluminescence (PL) spectra (c = 5 × 10−5 M) of dyads. Absorption spectrum of C60 is shown for reference. (middle) PL spectra of 3 (a-TTh), 4 (a-ThSe2), 5 (a-TThVin), and TTh (c = 10−5 M). (bottom) Absorption spectra of C60, TTh (terthiophene), and C60TTh together with the excitation spectrum of C60TTh (λcol = 714 nm). Asterisk (*) indicates harmonic peak of the collection wavelength. All experiments were recorded in CH2Cl2.
Figure 2. (top) Normalized UV–Vis absorption and photoluminescence (PL) spectra (c = 5 × 10−5 M) of dyads. Absorption spectrum of C60 is shown for reference. (middle) PL spectra of 3 (a-TTh), 4 (a-ThSe2), 5 (a-TThVin), and TTh (c = 10−5 M). (bottom) Absorption spectra of C60, TTh (terthiophene), and C60TTh together with the excitation spectrum of C60TTh (λcol = 714 nm). Asterisk (*) indicates harmonic peak of the collection wavelength. All experiments were recorded in CH2Cl2.
Materials 16 02605 g002
Materials 16 02605 g003 550
Figure 3. Absorption (black continuous lines) and excitation (λcol = 714 nm, cyan continuous lines) spectra of the C60 dyads. Dashed curves indicate fragments of absorption spectra multiplied by a factor of 10. Vertical dashed lines are shown as an eye guide. Asterisk (*) indicates harmonic peak of the collection wavelength. All experiments were recorded in CH2Cl2.
Figure 3. Absorption (black continuous lines) and excitation (λcol = 714 nm, cyan continuous lines) spectra of the C60 dyads. Dashed curves indicate fragments of absorption spectra multiplied by a factor of 10. Vertical dashed lines are shown as an eye guide. Asterisk (*) indicates harmonic peak of the collection wavelength. All experiments were recorded in CH2Cl2.
Materials 16 02605 g003
Materials 16 02605 g004 550
Figure 4. Set of UV–Vis spectra of tetraphenylcyclopentadienone (TPCPD) in CH2Cl2 in the presence of C60TTh upon illumination with xenon lamp. Inset: temporal decrease in the absorbance of tetraphenylcyclopentadienone (TPCPD) at 510 nm in the absence of PS (blank), the presence of TTh, C60TTh, C60TThVin, and C60ThSe2 during illumination with the xenon lamp.
Figure 4. Set of UV–Vis spectra of tetraphenylcyclopentadienone (TPCPD) in CH2Cl2 in the presence of C60TTh upon illumination with xenon lamp. Inset: temporal decrease in the absorbance of tetraphenylcyclopentadienone (TPCPD) at 510 nm in the absence of PS (blank), the presence of TTh, C60TTh, C60TThVin, and C60ThSe2 during illumination with the xenon lamp.
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Materials 16 02605 sch002 550
Scheme 2. Schematic representation of the proposed mechanism for singlet oxygen generation by the C60 dyads: (1) absorption of light by antenna A; (2) intersystem crossing within the antenna, 1A*→3A*, followed by triplet energy transfer from the antenna A to the C60, 3A*→3C60* (red trace); (3) singlet energy transfer from antenna A to C60, 1A*→1C60*, followed by intersystem crossing within C60, 1C60*→3C60* (green trace); (4) direct absorption of light by C60 leading to 1C60* states; (5) interaction of triplet oxygen 3O2 with 3C60* to form singlet oxygen 1O2.
Scheme 2. Schematic representation of the proposed mechanism for singlet oxygen generation by the C60 dyads: (1) absorption of light by antenna A; (2) intersystem crossing within the antenna, 1A*→3A*, followed by triplet energy transfer from the antenna A to the C60, 3A*→3C60* (red trace); (3) singlet energy transfer from antenna A to C60, 1A*→1C60*, followed by intersystem crossing within C60, 1C60*→3C60* (green trace); (4) direct absorption of light by C60 leading to 1C60* states; (5) interaction of triplet oxygen 3O2 with 3C60* to form singlet oxygen 1O2.
Materials 16 02605 sch002
Materials 16 02605 g005 550
Figure 5. Set of UV–Vis spectra of DHN in CH2Cl2 recorded in the presence of C60ThSe2 during illumination with xenon lamp. Inset: Increase in the absorbance at 420 nm over time recorded in the presence of C60, C60TTh, and C60ThSe2 during illumination with xenon lamp.
Figure 5. Set of UV–Vis spectra of DHN in CH2Cl2 recorded in the presence of C60ThSe2 during illumination with xenon lamp. Inset: Increase in the absorbance at 420 nm over time recorded in the presence of C60, C60TTh, and C60ThSe2 during illumination with xenon lamp.
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Table
Table 1. Summary of absorption, emission and photosensitizing parameters of the investigated dyads.
Table 1. Summary of absorption, emission and photosensitizing parameters of the investigated dyads.
Fullerene Dyadλabs/nm
(ε/104 M−1 cm−1)		λem/nmΦΔ
C60TTh258 (5.83),
328 (2.42),
430 (0.22)		714, 793, 9000.22 ± 0.02
C60TThVin258 (7.22),
328 (2.81),
430 (0.24)		714, 793, 9000.26 ± 0.01
C60ThSe2260 (9.02),
330 (3.29),
430 (0.23)		714, 793, 9000.31 ± 0.02
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Motyka, R.; Nastula, K.; Pander, P.; Honisz, D.; Tomczyk, M.; Erfurt, K.; Blacha-Grzechnik, A. S/Se-Terchalcogenophene-C60 Dyads: Synthesis and Characterization of Optical and Photosensitizing Properties. Materials 2023, 16, 2605. https://doi.org/10.3390/ma16072605

AMA Style

Motyka R, Nastula K, Pander P, Honisz D, Tomczyk M, Erfurt K, Blacha-Grzechnik A. S/Se-Terchalcogenophene-C60 Dyads: Synthesis and Characterization of Optical and Photosensitizing Properties. Materials. 2023; 16(7):2605. https://doi.org/10.3390/ma16072605

Chicago/Turabian Style

Motyka, Radosław, Klaudia Nastula, Piotr Pander, Damian Honisz, Mateusz Tomczyk, Karol Erfurt, and Agata Blacha-Grzechnik. 2023. "S/Se-Terchalcogenophene-C60 Dyads: Synthesis and Characterization of Optical and Photosensitizing Properties" Materials 16, no. 7: 2605. https://doi.org/10.3390/ma16072605

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