Supporting Information

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1 Supporting Information Conformational Transformation in Squaric cid Induced by Near-IR Laser Light Leszek Lapinski, Igor Reva, anna Rostkowska, nna alasa, Rui Fausto, and Maciej J. Nowak Institute of Physics, Polish cademy of Sciences, l. Lotnikow 32/46, Warsaw, Poland Department of Chemistry, University of Coimbra, Coimbra, Portugal transmittance, % wavenumber / cm 1 Figure S1. The measured transmission values of Edmund ptics longpass filters. fter near- IR irradiation of matrixes the spectra were collected using these filters. 1

2 0.4 absorbance 0.2 * * * (d) 0.5 (c) 500 km mol (b) wavenumber / cm -1 (a) Figure S2. Infrared spectra of squaric acid isolated in an r matrix (c) or in an N 2 matrix (d) compared with the infrared spectra, calculated at the DFT(B3LYP)/ G(d,p) level within harmonic approximation for conformers I (b) and II (a). The theoretical wavenumbers were scaled by the single factor of Experimental absorption bands originating from conformer II are marked with asterisks. 2

3 absorbance wavenumber / cm -1 Figure S3. Fragments of the infrared spectra of squaric acid isolated in an N 2 matrix. Upper panel: (black) after deposition of the matrix; (red) after 2 minutes of irradiation at 6849 cm -1 ; (blue) difference: red trace minus black trace. Lower panel: (black) after 5 minutes of irradiation at 6849 cm -1 ; (red) after 20 minutes of irradiation at 6849 cm -1 (blue) difference: red trace minus black trace. 3

4 conformer I 0.4 absorbance conformer II B 0.2 B wavenumber / cm -1 Figure S4. Effect of the spectrometer beam on the spectrum of squaric acid isolated in an N 2 matrix. Fragment of the infrared spectra recorded: (black) after deposition of the matrix; (red) after 30 minutes of near-ir irradiation at 6849 cm -1 ; after subsequent exposure of the matrix to the spectrometer beam for 3 minutes (magenta), 11 minutes (purple) and 21 minutes (blue). No filters were put between the spectrometer source and the nitrogen matrix. 4

5 B 7 0 absorbance B B B wavenumber / cm -1 Figure S5. Lower panel. Fragments of the infrared spectra of squaric acid isolated in an N 2 matrix recorded: (red) after 30 minutes of near-ir irradiation at 6849 cm -1 ; (orange and green) after subsequent exposure of the matrix for 3 and 15 minutes, respectively, to the spectrometer beam passed through the filter transmitting light with wavenumbers lower than 2200 cm -1 ; (gray, cyan and blue) after subsequent exposure of the matrix for 11, 20 and 35 minutes, respectively, to the spectrometer beam passed through the filter transmitting light with wavenumbers lower than 4200 cm -1. Upper panel. The effect of above irradiation shown as difference spectra: (red) - spectrum after exposure of the matrix for 3 min. to the filtered spectrometer light (ν ~ < 2200 cm -1 ) minus spectrum after 30 minutes of near-ir irradiation at 6849 cm -1 ; (orange) - spectrum after exposure of the matrix for 15 min. to the filtered spectrometer light (ν ~ < 2200 cm -1 ) minus spectrum after 30 minutes of near-ir irradiation at 6849 cm -1 ; (gray) - spectrum after subsequent exposure of the matrix for 11 min. to the filtered spectrometer light (ν ~ < 4200 cm -1 ) minus spectrum after exposure of the matrix for 15 min. to the filtered spectrometer light (ν ~ < 2200 cm -1 ); (cyan) - spectrum after subsequent exposure of the matrix for 20 min. to the filtered spectrometer light (ν ~ < 4200 cm -1 ) minus spectrum after exposure of the matrix for 15 min. to the filtered spectrometer light (ν ~ < 2200 cm -1 ); (blue) - spectrum after subsequent exposure of the matrix for 35 min. to the filtered spectrometer light (ν ~ < 4200 cm -1 ) minus spectrum after exposure of the matrix for 15 min. to the filtered spectrometer light (ν ~ < 2200 cm -1 ). 5

6 4500 Relative Energy / cm cm 1 ν cm 1 ν 7 τ s 465 cm 1 ν a 3517 cm 1 τ a cm 1 C s 0 C 2v Dihedral ngle --C=C / degrees Figure S6. The potential-energy profile for the interconversion between conformers I (C 2v ) and II (C s ) of squaric acid. ne of the --C=C torsional angles was used as a driving coordinate. The MP2/ G(d,p) calculations were carried out for a series of points with constrained values of the dihedral --C=C angle and all other degrees of freedom fully optimized. The horizontal lines at the bottom of potential wells designate energy levels of torsional vibrations in respective conformers (as observed for monomers of squaric acid in a nitrogen matrix). The horizontal lines at the top correspond to the fundamental energy levels of stretching vibrations in respective conformers (as observed for monomers of squaric acid in a nitrogen matrix). 6

7 Table S1. Symmetry coordinates used in the normal mode analysis for conformer I (C 2v symmetry) of squaric acid Definition Symmetry Symbol S 1 = (2-1/2 ) (r 7,9 + r 8,10 ) Α 1 ν s S 2 = (2-1/2 ) (r 7,9 - r 8,10 ) Β 2 ν a S 3 = (2-1/2 ) (r 3,7 + r 4,8 ) Α 1 ν s C S 4 = (2-1/2 ) (r 3,7 - r 4,8 ) Β 2 ν a C S 5 = (2-1/2 ) (r 1,5 + r 2,6 ) Α 1 ν s C= S 6 = (2-1/2 ) (r 1,5 - r 2,6 ) Β 2 ν a C= S 7 = r 1,2 Α 1 ν C 1 C 2 S 8 = r 3,4 Α 1 ν C 3 =C 4 S 9 = (2-1/2 ) (r 1,4 + r 2,3 ) Α 1 ν s CC S 10 = (2-1/2 ) (r 1,4 - r 2,3 ) Β 2 ν a CC S 11 = (2-1/2 ) (β 3,9,7 + β 4,10,8 ) Α 1 β s Ο S 12 = (2-1/2 ) (β 3,9,7 - β 4,10,8 ) Β 2 β a Ο S 13 =1/2 (β 2,5,1 - β 4,5,1 + β 1,6,2 - β 3,6,2 ) Α 1 β s C= S 14 =1/2 (β 2,5,1 - β 4,5,1 - β 1,6,2 + β 3,6,2 ) Β 2 β a C= S 15 =1/2 (β 4,7,3 - β 2,7,3 + β 3,8,4 - β 1,8,4 ) Α 1 β s C S 16 =1/2 (β 4,7,3 - β 2,7,3 - β 3,8,4 + β 1,8,4 ) Β 2 β a C S 17 =1/2 (β 3,1,4 - β 4,2,1 + β 1,3,2 - β 2,4,3 ) Β 2 β R S 18 = (2-1/2 ) (γ 5,2,1,4 + γ 6,3,2,1 ) Β 1 γ s C= S 19 = (2-1/2 ) (γ 5,2,1,4 - γ 6,3,2,1 ) Α 2 γ a C= S 20 = (2-1/2 ) (γ 7,4,3,2 + γ 8,1,4,3 ) Β 1 γ s C S 21 = (2-1/2 ) (γ 7,4,3,2 - γ 8,1,4,3 ) Α 2 γ a C S 22 =1/2 (τ 9,7,3,2 + τ 9,7,3,4 + τ 10,8,4,1 + τ 10,8,4,3 ) Β 1 τ s S 23 =1/2 (τ 9,7,3,2 + τ 9,7,3,4 - τ 10,8,4,1 - τ 10,8,4,3 ) Α 2 τ a S 24 =1/2 (τ 4,1,2,3 - τ 1,2,3,4 + τ 2,3,4,1 - τ 3,4,1,2 ) Α 2 τ R r i,j is the distance between atoms i and j ; β i,j,k is the angle between vectors k i and k j ; τ i,j,k,l is the dihedral angle between the plane defined by i, j, k and the plane defined by j, k, l atoms; γ i,j,k,l is the angle between the vector k i and the plane defined by atoms j, k, l. 7

8 Table S2. Internal coordinates used in the normal mode analysis for conformer II (C s symmetry) of squaric acid Definition Symmetry Symbol S 1 = r 7,9 ' ν 7 S 2 = r 8,10 ' ν 8 S 3 = (2-1/2 ) (r 3,7 + r 4,8 ) ' ν s C S 4 = (2-1/2 ) (r 3,7 - r 4,8 ) ' ν a C S 5 = (2-1/2 ) (r 1,5 + r 2,6 ) ' ν s C= S 6 = (2-1/2 ) (r 1,5 - r 2,6 ) ' ν a C= S 7 = r 1,2 ' ν C 1 C 2 S 8 = r 3,4 ' ν C 3 =C 4 S 9 = (2-1/2 ) (r 1,4 + r 2,3 ) ' ν s CC S 10 = (2-1/2 ) (r 1,4 - r 2,3 ) ' ν a CC S 11 = β 3,9,7 ' β Ο 7 S 12 = β 4,10,8 ' β Ο 8 S 13 =1/2 (β 2,5,1 - β 4,5,1 + β 1,6,2 - β 3,6,2 ) ' β s C= S 14 =1/2 (β 2,5,1 - β 4,5,1 - β 1,6,2 + β 3,6,2 ) ' β a C= S 15 =1/2 (β 4,7,3 - β 2,7,3 + β 3,8,4 - β 1,8,4 ) ' β s C S 16 =1/2 (β 4,7,3 - β 2,7,3 - β 3,8,4 + β 1,8,4 ) ' β a C S 17 =1/2 (β 3,1,4 - β 4,2,1 + β 1,3,2 - β 2,4,3 ) ' β R S 18 =(2-1/2 ) (γ 5,2,1,4 + γ 6,3,2,1 ) " γ s C= S 19 =(2-1/2 ) (γ 5,2,1,4 - γ 6,3,2,1 ) " γ a C= S 20 = γ 7,4,3,2 " γ C 3 7 S 21 = γ 8,1,4,3 " γ C 4 8 S 22 =1/2 (τ 9,7,3,2 + τ 9,7,3,4 + τ 10,8,4,1 + τ 10,8,4,3 ) " τ s S 23 =1/2 (τ 9,7,3,2 + τ 9,7,3,4 - τ 10,8,4,1 - τ 10,8,4,3 ) " τ a S 24 =1/2 (τ 4,1,2,3 - τ 1,2,3,4 + τ 2,3,4,1 - τ 3,4,1,2 ) " τ R r i,j is the distance between atoms i and j ; β i,j,k is the angle between vectors k i and k j ; τ i,j,k,l is the dihedral angle between the plane defined by i, j, k and the plane defined by j, k, l atoms; γ i,j,k,l is the angle between the vector k i and the plane defined by atoms j, k, l. 8

9 Table S3. Experimental wavenumbers (ν ~ /cm -1 ) and relative integral intensities (I) of the absorption bands decreasing upon near-ir (ν ~ = 6849 cm -1 ) irradiation of 3,4-dihydroxy-3-cyclobutene-1,2-dione isolated in Ne, r and N 2 matrixes, compared with wavenumbers (ν ~ /cm -1 ), absolute intensities ( th / km mol -1 ) and potential energy distribution (PED, %) calculated for the form I of C 2v symmetry. Experimental Calculated Ne matrix r Matrix N 2 matrix B3LYP/ G(d, p) ν ~ I a ν ~ I a ν ~ I a ν ~ b th PED c (%) ν s (100) 3587, 3582, w, ν a (100) 1843, , ν s C= (64), ν C 3 =C 4 (12), ν s C (12) , ν a C= (87) , 1670m , 1663w , 1665, ν C 3 =C 4 (39), ν s C= (24), ν s C (23) 1406sh, , 1396w , 1413, ν a C (67), ν a CC (17), β R (13) , β a (83), β a C (10) 1319w, , 1308w , β s (64), ν s C (18), ν s CC (12) , , ν s CC (30), ν C 3 =C 4 (30), β s (29) , , ν a CC (48), β a C= (15), ν a C (13), β a (12) ν C 1 C 2 (39), β s C= (29), ν s CC (13), ν s C (12) β a C= (60), β a C (34) γ a C= (83), τ R (18) ν s CC (34), ν s C (25), ν C 1 C 2 (24), ν C 3 =C 4 (10) β R (77), ν a C= (16) 9

10 γ s C= (50), γ s C (46) γ a C (105) , τ s (96) a Relative integrated intensities. b Theoretical positions of absorption bands were scaled down by a factor of c PED s lower than 10% are not included. Definition of symmetry coordinates is given in Table S1. w weak, sh shoulder τ a (99) β s C= (42), ν C 1 C 2 (30), β s C (20) β a C (45), ν a CC (29), β a C= (23) γ s C (54), γ s C= (46) β s C (69), β s C= (26) τ R (93), γ a C= (13) 10

Thermally and vibrationally induced conformational isomerizations, infrared spectra, and photochemistry of gallic acid in low-temperature matrices

Thermally and vibrationally induced conformational isomerizations, infrared spectra, and photochemistry of gallic acid in low-temperature matrices Licínia L. G. Justino, Igor Reva, and Rui Fausto Citation: