Comment pubs.acs.org/JPCA
Comment on “Photolysis of Polycyclic Aromatic Hydrocarbons on Water and Ice Surfaces” and on “Nonchromophoric Organic Matter Suppresses Polycyclic Aromatic Hydrocarbon Photolysis in Ice and at Ice Surfaces” Ján Krausko, Gabriela Ondrušková, and Dominik Heger* Department of Chemistry and RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
J. Phys. Chem. A 2014, 118 (9), 1638−1643. DOI: 10.1021/jp500263h J. Phys. Chem. A 2007, 111 (7), 1277−1285. DOI: 10.1021/jp066660t J. Phys. Chem. A 2015, 119. DOI: 10.1021/acs.jpca.5b09045 Anthracene fluorescence has been described in studies of naphthalene crystals.12 The energy transfer from naphthalene to anthracene present as a trace impurity is exothermic and is expected to occur effectively within individual crystal domains;12 moreover, it is often used for scintillators.13,14 Even ultralow levels (0.1 ppm) of anthracene admixed in crystalline naphthalene lead to the observation of sensitized anthracene fluorescence after the excitation of naphthalene.12 In recrystallized naphthalene on gold surfaces, a luminescence band at 415 nm was observed in addition to the excimeric band at 400 nm and described to be of an “extrinsic nature”.15 A thorough purification procedure including refluxing with sodium or potassium and the subsequent repeated zonemelting (up to 200 passes) was needed to obtain naphthalene free of anthracene from commercially available chemicals of high purity (98−99% or higher).12,16 Eighty passes in the zonemelting refinement were apparently not sufficient to remove all the impurities, and therefore there was some vibrationally resolved structure (probably due to anthracene) on the top of the broad excimeric emission spectrum in Kawakubo’s report.3 In later publications, after more thorough purification by 200 passes of the molten zone during the zone-melting refinement, the fluorescence of anthracene was absent in the spectra of naphthalene crystals reported by Kawakubo and Uchida.7,16 The fact that the sensitized emission of anthracene can be measured in naphthalene crystals (Figure 1; Fluka, analytical standard) and in a frozen aqueous solution prepared from the same material leaves no doubt that the vibrationally resolved emission reported in the commented papers1,2 should be ascribed to anthracene impurity and not to the naphthalene excimer emission. The intensities reported in the commented papers are substantially higher than those observed by us, which may be attributed to the different purity of the chemicals used (98%1 and 99+%;2 our work >99.7% Fluka, analytical standard9). We noticed that the confusion of the sensitized emission of anthracene with the emission of naphthalene excimers can be found in other scientific fields as well.17 The discussed spectra in commented papers can be due to direct excitation of both naphthalene and anthracene and thus do not
In commented papers, Kahan and Donaldson1 and Malley and Kahan2 reported the observation of a structured emission with bands at 377, 387, 409, 433, and 461 nm and at 386, 408, and 434 nm, respectively,1,2 from frozen solutions of naphthalene in water, which they assigned to excimer emission from naphthalene. To support their assignment, the authors referred to the spectral measurements of naphthalene in frozen organic solvents performed by Kawakubo.3 Naphthalene is known to exhibit a broad luminescence band for highly concentrated solutions at room temperature in each of the following solvents: hexane (λmax = 383 nm),4 toluene (386 nm),5 and dimethyl sulfoxide (389 nm).4 The same longwavelength band was also observed at 207 K in frozen toluene (397 nm),6 at 77 K in thin naphthalene films and microcrystals (400 nm),7 and in numerous other environments. All these emissions were assigned to excimer fluorescence. We observed the excimeric emission of both benzene8 and naphthalene9 in the frozen aqueous solutions as a broad shoulder extending bathochromically from the emission of each monomer. Broad featureless bands are a general characteristic of excimeric emission.10 We were, therefore, surprised to see that an emission with a well-resolved vibrational structure from frozen aqueous solutions of naphthalene was assigned to naphthalene excimers.1,2 In our ongoing study of ice doped with additives we, too, utilized naphthalene (>99.7% Fluka, analytical standard)9 and obtained emission spectra similar to those in commented papers1,2 with bands at 387, 412, and 437 nm (Figure 1). However, the intensities of these bands were much smaller in our experiments. In fact, we did not observe these bands with each frozen sample; sometimes, their intensities were within the noise level (compare the black line in Figure 1a to the black line in Figure 1b). A solution to this puzzle was found by attributing the presumptive naphthalene excimer peaks to the luminescence of anthracene. The observed emission peaks show a regular solvatochromic shift of (575 ± 77) cm−1 from those of anthracene in water9 and of (411 ± 52) cm−1 for anthracene in methylcyclohexane.11 A mixed aqueous solution of naphthalene (8 × 10−5 M) and anthracene (2 × 10−8 M) was frozen to show that the anthracene fluorescence peaks exhibit a higher intensity but otherwise exactly match the positions of those observed for the “pure” naphthalene frozen solution.9 © XXXX American Chemical Society
Received: August 25, 2015 Revised: October 9, 2015
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DOI: 10.1021/acs.jpca.5b08276 J. Phys. Chem. A XXXX, XXX, XXX−XXX
Comment
The Journal of Physical Chemistry A Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors wish to thank Joggi Wirz for the helpful discussions and support. This project was supported by the National Sustainability Programme of the Czech Ministry of Education, Youth and Sports (LO1214) and the RECETOX research infrastructure (LM2011028) and the Czech Science Foundation (GA15-12386S).
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Figure 1. Fluorescence emission spectra of (a) frozen aqueous naphthalene solution at 77 K (black line, 7.8 × 10−5 M, λexc= 274 nm); frozen mixture of aqueous solution of naphthalene (7.8 × 10−5 M) and anthracene (1.7 × 10−8 M) at 77 K (light blue line); and aqueous solution of anthracene at room temperature (magenta line, λexc = 333 nm) and (b) frozen aqueous naphthalene solution at 77 K (black line, 7.8 × 10−5 M, λexc = 274 nm); naphthalene crystals at room temperature (dark blue line, λexc = 300 nm); frozen mixture of aqueous solution of naphthalene (7.8 × 10−5 M) and anthracene (1.7 × 10−8 M) at 77 K (light blue line); and frozen solution of naphthalene digitalized from the commented paper2 (red line).
provide any information about aggregation. The present findings have important implications for the interpretation of compartmentation of impurities in ice and the derived environmental implications, both in our work and that of Kahan and Donaldson.18,19
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REFERENCES
(1) Kahan, T. F.; Donaldson, D. J. Photolysis of Polycyclic Aromatic Hydrocarbons on Water and Ice Surfaces. J. Phys. Chem. A 2007, 111, 1277−1285. (2) Malley, P. P. A.; Kahan, T. F. Nonchromophoric Organic Matter Suppresses Polycyclic Aromatic Hydrocarbon Photolysis in Ice and at Ice Surfaces. J. Phys. Chem. A 2014, 118, 1638−1643. (3) Kawakubo, T.; Okada, M.; Shibata, T. Excimer (Excited Dimer) Fluorescence of Naphthalene at 77 Degrees K in Rigid Media. J. Phys. Soc. Jpn. 1966, 21, 1469−1470. (4) Castanheira, E. M. S.; Martinho, J. M. G. Solvatochromic Shifts of Naphthalene and Pyrene Excimers. J. Photochem. Photobiol., A 1994, 80, 151−156. (5) Kazzaz, A. A.; Munro, I. H. Naphthalene Excimer Emission. Proc. Phys. Soc., London 1966, 87, 329−330. (6) Forster, T. Excimers. Angew. Chem., Int. Ed. Engl. 1969, 8, 333− 343. (7) Uchida, K.; Tanaka, M.; Tomura, M. Excimer Emission of Crystalline Naphthalene. J. Lumin. 1979, 20, 409−414. (8) Kania, R.; Malongwe, J. K. E.; Nachtigallová, D.; Krausko, J.; Gladich, I.; Roeselová, M.; Heger, D.; Klán, P. Spectroscopic Properties of Benzene at the Air−Ice Interface: A Combined Experimental−Computational Approach. J. Phys. Chem. A 2014, 118, 7535−7547. (9) Krausko, J.; Malongwe, J. K. E.; Bičanová, G.; Klán, P.; Nachtigallová, D.; Heger, D. Spectroscopic Properties of Naphthalene on the Surface of Ice Grains Revisited: A Combined Experimental− Computational Approach. J. Phys. Chem. A 2015, 119, 8565−8578. (10) Birks, J. B. Excimers. Rep. Prog. Phys. 1975, 38, 903−974. (11) Chandross, E. A.; Schiebel, A. H. Absorption and Exciplex Emission-Spectra of Naphthalene-Anthracene Sadwich Pair. J. Am. Chem. Soc. 1973, 95, 1671−1672. (12) Auweter, H.; Braun, A.; Mayer, U.; Schmid, D. Dynamics of Energy-Transfer by Singlet Exctons in Naphthalene Crystals as Studied by Time-Resolved Spectroscopy. Z. Naturforsch., A: Phys. Sci. 1979, 34, 761−771. (13) Balamurugan, N.; Arulchakkaravarthi, A.; Ramasamy, P. Scintillation Characteristics on Anthracene-Doped Naphthalene Crystal for Cs-137-Gamma Ray Source. Nucl. Instrum. Methods Phys. Res., Sect. A 2006, 568, 767−771. (14) Balamurugan, N.; Arulchakkaravarthi, A.; Ramasamy, P. Luminescence Properties and Growth of Pure and AnthraceneDoped Naphthalene Crystals. Phys. Status Solidi A 2007, 204, 3502− 3508. (15) Nakayama, H.; Hosokawa, T.; Ishii, K. Fluorescence Spectra and Energy Transfer in Amorphous Naphthalene. Chem. Phys. Lett. 1998, 289, 275−280. (16) Kawakubo, T. Emission of Naphthalene and Some of Its Derivatives in Crystalline State. Mol. Cryst. Liq. Cryst. 1972, 16, 333− 353. (17) Dai, J.; McKee, M. L.; Samokhvalov, A. Adsorption of Naphthalene and Indole on F300 Mof in Liquid Phase by the Complementary Spectroscopic, Kinetic and Dft Studies. J. Porous Mater. 2014, 21, 709−727. (18) Kahan, T. F.; Wren, S. N.; Donaldson, D. J. A Pinch of Salt Is All It Takes: Chemistry at the Frozen Water Surface. Acc. Chem. Res. 2014, 47, 1587−1594.
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[email protected]. Funding
This project was supported by the National Sustainability Programme of the Czech Ministry of Education, Youth and Sports (LO1214) and the RECETOX research infrastructure (LM2011028) and the Czech Science Foundation (GA15− 12386S). B
DOI: 10.1021/acs.jpca.5b08276 J. Phys. Chem. A XXXX, XXX, XXX−XXX
Comment
The Journal of Physical Chemistry A (19) Bartels-Rausch, T.; Jacobi, H. W.; Kahan, T. F.; Thomas, J. L.; Thomson, E. S.; Abbatt, J. P. D.; Ammann, M.; Blackford, J. R.; Bluhm, H.; Boxe, C.; et al. A Review of Air−Ice Chemical and Physical Interactions (Aici): Liquids, Quasi-Liquids, and Solids in Snow. Atmos. Chem. Phys. 2014, 14, 1587−1633.
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DOI: 10.1021/acs.jpca.5b08276 J. Phys. Chem. A XXXX, XXX, XXX−XXX
