Inner-filter absorption of the exciting light by the quencher or may be cause of large errors in the evaluation of quenching efficiencies in measurements of fluorescence quenching. We performed fluorescence measurements of 5,10,15,20-tetraphenylporphyrin toluene solution in a wide concentration range. We have shown a Förster-free fluorescence quenching in a right-angle geometry experiment, caused by second order inner filter. We proposed to perform measurements in a front-surface geometry to investigate the nature of quenching not related to the inner filters. We have shown that concentration effects in tetraphenylporphyrin solutions in toluene are not accompanied by a decrease in the fluorescence intensity in a front-surface geometry at concentrations of 10− 3-10− 7 mol/l. It was possible to separate the phenomena of the internal filters from the processes occurring in a liquid medium. Our results are of great importance due to the widespread fundamental research of porphyrin-based dyes properties.
Research Article
Förster-free effect fluorescence quenching of 5,10,15,20-tetraphenylporphyrin in solution
https://doi.org/10.21203/rs.3.rs-2889312/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 12 Jun, 2023
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tetraphenylporphyrin
photoluminescence
fluorescence
self-quenching
absorption
re-absorption
inner filter effect
- The Förster-free effect fluorescence is observed up to closed to the ultimate solubility concentrations in tetraphenylporphyrins toluene solution at concentrations of 10-3-10-7 mol/l.
- Förster radius was estimated for 5,10,15,20-tetraphenylporphyrin molecules.
- Concentration quenching of tetraphenylporphyrin solutions was studied in a wide range of concentrations
- A correction experimental method is proposed conditions to minimize inner filter effects
In recent times, the field of new organic compounds synthesis with unique optical and photophysical properties has attracted much attention due to their abundance and the possibility to use their properties in many potential optoelectronic applications [1, 2]. This group of compounds includes materials based on tetraphenylporphyrins. The tetraphenylporphyrin molecule is a tetrapyrrole macrocycle connected by methyl bridges, with phenyl groups attached at positions 5, 10, 15 and 20. However, they differ from a huge variety of other groups of macrocyclic compounds in that they are aromatic macrocycles with a unique conjugated π-system, which ultimately determines their essence as biological [3] and industrial catalysts [4], thermal [5], light and chemical sensitizer [6] and biologically active compounds [6]. Functional groups can be replaced, forming a wide range of porphyrin derivatives, which can significantly improve the functionality of porphyrins, expanding their use [7, 8]. In addition, porphyrins have semiconductor properties and strong light absorption in the ultraviolet and visible regions, which allows to use them as a material for solar cells, photocatalysis and photosynthesis systems [2, 7–11]. In most cases, re-absorption and self-absorption effects are observed in high absorbing mediums [12], which misrepresents the experiment data. Such effects are evident in the form of quenching and self-quenching processes. The most common cause of self–quenching are inner filter effects (IFE) [13]. The inner filter effects are common problems in fluorescence spectroscopy, affecting spectral measurements in particular[14]. There are the primary and the secondary IFE. Primary one appears as the absorption of exciting light by the sample volume. In highly concentrated solutions the excitation beam is attenuated by the sample so that only the surface facing the excitation beam fluoresces strongly. With a large absorption of the laser, only the surface layer remains luminescent which affects at the final outcome. Herewith, an incorrect interpretation of the experimental data as a decrease in photoluminescence is possible. The absorption of its own irradiation is called secondary IFE. This happens if there is an overlap of the luminescence and absorption spectra. The inner filter effect results in spectral distortion and in some cases complete loss of signal. Above effects should be minimized in works related to the study of the optical properties of composite materials and solutions, where the task is to study the processes of energy transfer between components. Such experimental features as an excitation energy, a spectra registration geometry [13, 14], as well as a concentration of solutions may influence to the self-quenching. The strongest concentration quenching was observed in [15] in the concentration range of 1.5∙10− 7-6.1∙10− 3 mol/l, which is quite unusual for such low concentrations. The authors [15] explained this by the Foerster effect. We decided to study this phenomenon in detail, since the result of the experiment may depend on the methodology. Laser infused photoluminescence of H2TPP toluene solution in a wide concentration range of have been assessed in the present work. No comparisons of optical spectroscopy results obtained with different geometries have been carried out before. We presented results obtained by measuring in two position of the sample and the laser. Fluorescence properties as inner filter effects were examined and revealed to be strongly dependent on concentration and detection geometry. Förster radius was estimated for 5,10,15,20-tetraphenylporphyrin molecules.
H2TPP (5,10,15,20-Tetraphenylporphyrin, Sigma-Aldrich 99% low chlorin) was chosen as the materials for research. H2TPP molecule is shown in Fig. 1 according to our early quantum chemical calculations [16]. To study the effect of concentration on the H2TPP fluorescence in liquid medium, we used toluene as a solvent for its better solubility It is optically transparent in the studied spectral range. Moreover, toluene does not require any additional operations to improve solubility, such as ultrasonic baths, heating or filtration to ensure complete solubility. Photoluminescence spectra were measured by an automated setup based on a monochromator with a 600-bar/mm diffraction grating and a photomultiplier tube detector. Photoluminescence was excited by a 405 nm continuous wave semiconductor laser with the power of 40 mW, the spot size was 1 mm. Such laser wavelength provides excitation to the Sore band. A yellow glass filter was installed in front of the input slot of the monochromator to avoid scattered 408 nm laser radiation. The optical absorption spectra were measured using a Shimadzu UV 3600 Plus spectrophotometer.
3.1. Right-angle geometry quenching
The absorption spectra were measured at a low concentration of 10− 8 mol/l at the first stage of our study and presented in Fig. 1a. A low concentration is necessary to exclude aggregation processes – the formation of supramolecular ensembles, which may change the shape and position of the spectrum. An intense Soret band or B-zone is observed in the short-wavelength region of the absorption spectrum at 200–450 nm, which corresponds to the allowed transitions with a maximum at 419 nm. 4 bands equidistant from each other are observed in the visible spectral region, which are numbered according to the Stern (Q bands). Their intensity is 5 times lower than for the Soret band. Q-band has vibrational peaks at 514 nm (QY(1,0)), 548 nm (QY(0,0)), 592 nm (QX(1,0)) and 648 nm (QX(0,0)). The photoluminescence (PL) spectrum is presented next to the absorption one on Fig. 1a. PL spectra, in general, consist of two maxima corresponding to a S1→S0 + hνf electron transition with an energy of 1.9-2 eV (655 nm) and to its vibrational sublevel – 1.7–1.8 eV (718 nm), where S1 is the first excited singlet state, S0 is the main singlet state, hνf is the phonon energy [17]. The short-wave band observed in other works [18] which is associated with transitions S2→S0 from the second excited state with an energy of 2.8 eV (450 nm) was not detected in our work due to its proximity to the excitation energy. The diagram of transitions in the electronic structure of porphyrin [19, 20] is shown in Fig. 1b. In fact, the emission from the samples in our experiment is fluorescence. Phosphorescence with long lifetimes is not observed here. It is not hard to notice a mirror symmetry in an absorption and a luminescence spectrum. This phenomenon may be observed when: 1 – the oscillation frequencies in the spectrum are the same for the ground and the excited states; 2 – the dipole moment matrix element of an electron-vibrational transition does not depend on which state the oscillation is applied to; 3 – the distribution function over vibrational states is the same for the ground and the excited states. The cross-point is the energy of the electronic transition at 1.9 eV for our samples. We observe a rather significant overlap of the first absorption band and 655 nm fluorescence maximum as well as a partial overlap of the absorption tail and the 720 nm PL maximum. It may lead to a decrease in the fluorescence intensity which is a quenching.
Processes associated with the PL quenching in liquid mediums may be associated with such physical phenomena as: 1 – the primary inner filter effect is the process of absorption of laser exciting radiation in the solution volume (shown in Fig. 2); 2 – secondary inner filter effect which is an absorption of intrinsic fluorescence by unexcited molecules in the volume of the solution; 3. Förster or fluorescence resonance energy transfer (FRET), which is a mechanism describing energy transfer between two light-sensitive molecules. A donor, initially in its electronic excited state, may transfer energy to an acceptor through nonradiative dipole–dipole coupling. The efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor, making FRET extremely sensitive to small changes in distance and obviously in concentration. Looking ahead, we observed that all these processes exist concurrently. The geometry in which the radiation spectrum is fixed has a strong influence. We used various experimental techniques to separate mentioned processes.
The measurement results at a concentration of 10− 6 mol/l are shown in the Fig. 4. Normalized spectra are shown in the inset to the Fig. 4. All fluorescence measurements of TPP toluene solution were provided by 405 nm laser excitation to the Soret band as the region with the highest absorption. The laser beam installation, passing through the cuvette, corresponds to points 1–4 (showed in Fig. 4), which corresponds to the distances at points: 1 – directly in focus, the excited PL does not pass through the thickness of the solution, 2 – at the thickness of the solution 0.5 cm, 3–1 cm, 4–1.8 cm. This means that the excited PL passes through 1.8 cm of the solution to the point of focus and detection. The concentration was selected so that the laser passed through the cuvette to minimize the primary internal filter. As a result, there is two-times decrease of the intensity of the right maximum at a point 4. The left maximum shifts to the long-wave region. A step appears in the region of 640 nm, which is located near the intersection point of the absorption and PL spectra. This is due to the incomplete overlap of the absorption and PL spectra. It should be noted that almost complete PL quenching in the overlap area occurs already at a distance of 0.5 cm from focus (point 2). A further decrease in the intensity of whole spectra is associated with an overlap of the PL spectrum with the absorption tail (see Fig. 1). It is possible to observe the absence of typical presence of the Förster charge transfer, such as the quenching of only definite bands and re-emission to another bands. To confirm this hypothesis, we compared the estimated Förster radius and the distance between molecules at different concentrations.
The Förster radius was calculated according to the well-known way [21, 22],
$${R}_{0}^{6}=\frac{9000\text{ln}10}{128 {\pi }^{5}{N}_{A}} \frac{{\kappa }^{2}{\varphi }_{f}}{{n}^{4}} J \tilde10 nm$$
1
where \(\kappa\) – dipole orientation factor, \({\varphi }_{f}\) – the quantum yield of the donor fluorescence in the absence of the acceptor, NA – is Avogadro number, J – refers to the spectral overlap between the emission and absorption bands.
The distance between molecules at a definite concentration:
where CM – a molar concentration, V – a volume of a solution. We obtained the distance between the molecules of 220, 35 and 10 nm at concentrations of 10− 7, 10− 5 and 10− 3 mol/l respectively, using formula (2). These values are greater than the typical Förster radius at which resonant energy transfer is possible. The Förster energy transfer becomes possible only at concentrations above 5∙10− 3 mol/l. However, such concentrations are close to the ultimate solubility, according to our data and our experiment conditions.
Therefore, such a phenomenon should be studied in solid phases (films) and in aggregates [23–25], and not observed for solutions.
3.2. Front-surface geometry experiment
The inner filter effects may be minimized when registering the fluorescence in the front-surface geometry. The laser beam falls at an angle of about 45 degrees to the surface of the solution (cuvette front surface). The signal focus is fixing in the same plane. Maximum luminescence is observed at the falling beam point, so further processes occurring in the volume of the solution do not affect at the result. Results of the photoluminescence measuring of solutions at different concentrations are shown in Fig. 5. A wide range of concentrations from 10− 7 to 10− 3 mol/l was considered. Result showed the absence of concentration quenching in the whole concentration range. The dependences of the separated maxima intensities from the concentration are shown in the Fig. 5b. A sublinear increase of fluorescence intensity is observed in a logarithmic scale up to concentrations of 10− 3 mol/l. This means a power-law dependence of the intensity growth with a degree of 1/4, which may be explained by the effect of a secondary inner filter at low concentrations. The nature of the power dependence changes for the last two points on the graphs at the concentration values of 1∙10− 3 mol/l. This probably happens because of the self-absorption at high concentrations. Förster charge transfer is also possible, because the distance between molecules becomes less than 10 nm. However, the impact of these processes is not so significant and does not lead to an intensity decrease with a concentration increase. Firstly, the absorption and luminescence overlap region is only a few percent of the total absorption for concentration over 10− 6 mol/l. There is only a small volume of the solution could luminesce because of the absorption of laser radiation is much stronger. Secondly, at concentrations below 10− 3 mol/l, the Förster charge transfer is impossible for the reasons mentioned above. The solubility limit of the H2TPP in toluene is reached higher than 10− 3 mol/l, which was experimentally determined. Moreover, we suppose that it is impossible to observe concentration quenching for this choice of material and solvent. Here the primary inner filter has the greatest impact. Due to this, only a small volume of the solution can luminesce - not so much of its own PL is distributed among non-luminescent molecules.
We have shown that photoluminescence quenching in 5,10,15,20-tetraphenylporphyrin solutions in toluene occur mainly due to first and second order inner filters effects at concentration of 10− 3-10− 7 mol/l. Förster-free fluorescence quenching in a right-angle geometry experiment, caused by second order inner filter. To prove this statement, we calculated the Förster radius and compared it with the distance between the molecules at mentioned concentrations. It turned out that the typical radius which leads to resonant energy transfer is less than the distance between molecules at our concentrations. Therefore, Förster effect might not to be observed. We proposed a measurement in front-surface geometry to minimize the impact of inner filter effects. We did not observe a decrease in the intensity of photoluminescence with an increase in concentration in this case. This indicates that we have managed to avoid the influence of the IFE. At the same time, there are no other processes leading to PL quenching.
Author contributions
All authors have equal contribution to the study.
Data availability
The raw data are available at the corresponding author and can be presented for reasonable requests.
Declarations
Conflict of interest
The authors declare that they have no conflict of interest.
Fundings
This work was not supported by any fundings.
- El-Mahalawy, A.M., Nawar, A.M., Wassel, A.R.: Efficacy assessment of metalloporphyrins as functional materials for photodetection applications: role of central tetrapyrrole metal ions Electronic materials. https://doi.org/10.1007/s10853-022-07574-1
- Wang, X., Lu, Y., Zhang, J., Zhang, S., Chen, T., Ou, Q., Huang, J.: Highly Sensitive Artificial Visual Array Using Transistors Based on Porphyrins and Semiconductors. Small. 17, 2005491 (2021). https://doi.org/10.1002/smll.202005491
- Zhang, H., Han, W., Han, J., Xu, P., Jiang, P.: Review of novel materials as photosensitizers towards the bottleneck of photodynamic therapy. J. Mater. Sci. 2022 5731. 57, 14620–14654 (2022). https://doi.org/10.1007/S10853-022-07529-6
- Barona-Castaño, J., Carmona-Vargas, C., Brocksom, T., de Oliveira, K.: Porphyrins as Catalysts in Scalable Organic Reactions. Molecules. 21, 310 (2016). https://doi.org/10.3390/molecules21030310
- Dmitrieva, O.A., Mamardashvili, N.Z.: Porphyrin dimer as efficient optical thermometer: Experimental and computational evaluation of the barrier to torsional rotation. J. Lumin. 235, 117986 (2021). https://doi.org/10.1016/J.JLUMIN.2021.117986
- Ji, J.M., Zhou, H., Kim, H.K.: Rational design criteria for D–π–A structured organic and porphyrin sensitizers for highly efficient dye-sensitized solar cells. J. Mater. Chem. A. 6, 14518–14545 (2018). https://doi.org/10.1039/C8TA02281J
- Ji, W., Wang, T.X., Ding, X., Lei, S., Han, B.H.: Porphyrin- and phthalocyanine-based porous organic polymers: From synthesis to application. Coord. Chem. Rev. 439, 213875 (2021). https://doi.org/10.1016/J.CCR.2021.213875
- Zarrabi, N., Poddutoori, P.K.: Aluminum(III) porphyrin: A unique building block for artificial photosynthetic systems. Coord. Chem. Rev. 429, (2021). https://doi.org/10.1016/J.CCR.2020.213561
- Singh, C., Chaubey, S., Singh, P., Sharma, K., Shambhavi, Kumar, A., Yadav, R.K., Dwivedi, D.K., Baeg, J.O., Kumar, U., Yadav, B.C., Pandey, G.: Self-assembled carbon nitride/cobalt (III) porphyrin photocatalyst for mimicking natural photosynthesis. Diam. Relat. Mater. 101, 107648 (2020). https://doi.org/10.1016/J.DIAMOND.2019.107648
- Shi, Y., Zhang, F., Linhardt, R.J.: Porphyrin-based compounds and their applications in materials and medicine. Dye. Pigment. 188, 109136 (2021). https://doi.org/10.1016/J.DYEPIG.2021.109136
- Lukomsky, I., Gottfried, V., Kimel, S.: Delayed fluorescence of porphyrins in different media. J. Fluoresc. 4, 49–51 (1994). https://doi.org/10.1007/BF01876653/METRICS
- O’Neal, J.S., Schulman, S.G.: Determination of Fluorescence Efficiencies of Fluorophores in Highly Absorbing Solutions Using Right Angle Geometry. http://dx.doi.org/10.1080/00032718608064514. 19, 495–501 (2006). https://doi.org/10.1080/00032718608064514
- Credi, A., Prodi, L.: Inner filter effects and other traps in quantitative spectrofluorimetric measurements: Origins and methods of correction. J. Mol. Struct. 1077, 30–39 (2014). https://doi.org/10.1016/J.MOLSTRUC.2014.03.028
- Kumar Panigrahi, S., Kumar Mishra, A.: Inner filter effect in fluorescence spectroscopy: As a problem and as a solution. J. Photochem. Photobiol. C Photochem. Rev. 41, 100318 (2019). https://doi.org/10.1016/J.JPHOTOCHEMREV.2019.100318
- Ghosh, M., Nath, S., Hajra, A., Sinha, S.: Fluorescence self-quenching of tetraphenylporphyrin in liquid medium. J. Lumin. 141, 87–92 (2013). https://doi.org/10.1016/j.jlumin.2013.03.025
- Elistratova, M.A., Zakharova, I.B., Kvyatkovskii: Self-organization features of tetraphenylporphyrins according to quantum chemical calculations. Macroheterocycles. 12, 370–374 (2019). https://doi.org/10.6060/mhc190552e
- Harriman, A.: Luminescence of porphyrins and metalloporphyrins. Part 1. - Zinc(II), nickel(II) and manganese(II) porphyrins. J. Chem. Soc. Faraday Trans. 1 Phys. Chem. Condens. Phases. 76, 1978–1985 (1980). https://doi.org/10.1039/F19807601978
- O’Brien, J.A., Rallabandi, S., Tripathy, U., Paige, M.F., Steer, R.P.: Efficient S2 state production in ZnTPP-PMMA thin films by triplet-triplet annihilation: Evidence of solute aggregation in photon upconversion systems. Chem. Phys. Lett. 475, 220–222 (2009). https://doi.org/10.1016/j.cplett.2009.05.039
- Nurhayati, Suendo, V., Alni, A., Nugroho, A.A., Majima, Y., Lee, S., Nugraha, Y.P., Uekusa, H.: Revealing the Real Size of a Porphyrin Molecule with Quantum Confinement Probing via Temperature-Dependent Photoluminescence Spectroscopy. J. Phys. Chem. A. 124, 2672–2682 (2020). https://doi.org/10.1021/ACS.JPCA.0C00665
- Nurhayati, Suendo, V., Nugroho, A.A., Alni, A.: Temperature-dependent photoluminescence of H2TPP and ZnTPP thin films on Si substrates. IOP Conf. Ser. Mater. Sci. Eng. 858, 012036 (2020). https://doi.org/10.1088/1757-899X/858/1/012036
- Sinha, S., De, R., Ganguly, T., De, A.K., Nandy, S.K.: Studies on quenching reactions in the excited electronic states of tetrahydronaphthols both at the ambient temperature as well as at 77 K. J. Lumin. 75, 99–116 (1997). https://doi.org/10.1016/S0022-2313(97)00114-2
- Chou, K.F., Dennis, A.M., Hildebrandt, N., Medintz, I., Algar, R.: Förster Resonance Energy Transfer between Quantum Dot Donors and Quantum Dot Acceptors. Sensors 2015, Vol. 15, Pages 13288-13325. 15, 13288–13325 (2015). https://doi.org/10.3390/S150613288
- Zakharova, I.B., Elistratova, M.A., Romanov, N.M., Kvyatkovskii, O.E.: Specific Features of the Electron Structure of ZnTPP Aggregated Forms: Data of Optical Measurements and Quantum-Chemical Calculations. Semiconductors. 52, (2018). https://doi.org/10.1134/S1063782618130237
- Nath Bera, R., Sakakibara, Y., Tokumoto, M.: Concentration quenching of a red emitting electroluminescent dye tetraphenylporphyrin: A time-resolved photoluminescence study. J. Mater. Sci. Mater. Electron. 16, 549–552 (2005). https://doi.org/10.1007/s10854-005-2731-4
- Aydin, M.: DFT and Raman spectroscopy of porphyrin derivatives: Tetraphenylporphine (TPP). Vib. Spectrosc. 68, 141–152 (2013). https://doi.org/10.1016/j.vibspec.2013.06.005
No competing interests reported.