J. Phys. Chem. 1992,96, 10225-10234
10225
Ultraviolet Stablllzers of the 2 4 Hydroxyphenyl)benzotriazole Class. Influence of Substituents on Structure and Spectra Jocben Rieker? Eke Lemmert-S~hmitt,~ Gernot Goeller? Manfred Roessler? Cuido J. Stueber? Heike Scbettler,f Horst E. A. Kramer,*It John J. Stezowski,**#Helga Hoier,*Sonja Henkel,t Armin Schmidt,, Helmut Port,l Martin Wiecbmam,* Jean R d y , ” Gerhard Rytz,ll Mario Slongo,ll and Jean-Luc Birbaumll Institute far Physikalische Chemie, Organische Chemie und Isotopenforschung, und Anorganische Chemie, Universitdt Stuttgart, Pfaffenwaldring 55, D- 7000 Stuttgart 80,Germany: Physikalisches Institut, Universitdt Stuttgart, Pfaffenwaldring 57, 0-7000 Stuttgart 80,Germany; and Ciba-Geigy Ltd., Additives Division (AD 2.1). Research Centre Fribourg, CH-I 723 Marly 1, Switzerland (Received: July 29, 1992)
X-ray crystal structure determinations are reported for 2-(3’-fert-butyl-2’-hydmxy-5’,6’dimethylphenyl)benzo~le(HM-TIN), 2-(3’-ter~-butyl-2’-hydroxy-5’-methylphenyl)benzotriazole (HTBM-TIN), and 2-(2’,4’-dihydroxy-6’-methylphenyl)tm”le (HH-TIN). In contrast to 2-(2’-hydroxy-5’-methyl)benzotriamle(R = H,trade name Tinuvin P (TIN P)) and HTBM-TIN (dihedral angle 5.1’) there is no planar arrangement of the bonded benzotriazole and the substituted phenol rings within one molecule in the neat crystal (dihedral angles: HM-TIN, 89.3’; HH-TIN, 59.8O (crystallizedat 293 K) and 89.9O (crystallized at 277 K)). There is a strong influenceof crystallization temperature on crystal packing for HH-TIN. UV absorption spectra of HM-TIN and HH-TIN in unpolar fluid solvents suggest the existence of a weak intramolecular hydrogen bond, Methyl and/or tert-butyl subtituents in the 3’ and/or 5’ position and particularly a CH30substituentin the 5 position of the be”mle ring strengthen the intramolecular hydrogen bond as revealed by IR spectrmpy of the solids and UV absorption spectroscopy in solvents of different polarity. MOHTM-TIN (2-(3’-tert-butyl-2’-hydroxy-5’-methylphenyl)-5-methoxybenzotriazole), whose intramolecularhydrogen bond is stronger than that of TIN P,provides a higher yield of the proton-transferredfluorescence and-in contrast to TIN P-no phosphorescence in EPA. Time-resolved measurements of BHDTB-TIN (2-(3’,5’-di-terrbutyl-2’-hydroxyphenyl)-5-(a,a’-dimethylbenzyl)benzotriazole), DHDTB-TIN (2-(3’,5’-di-tert-butyl-2’,6’-dihydroxyphenyl)benzotriazole), and MOHTM-TIN at 293 K show red fluorescence in hexane (&, 700 nm, f < 5 p),while 420 nm, rF 1 ns) and red emissions are observed. in DMSO blue (&
-
Introduction The intact intramolecular hydrogen bond is of fundamental importance for the stabilizing efficiency of UV absorbers such as methyl salicylate, o-hydroxybenzophenones, derivatives of 2-hydroxyphenyl-1,3,5-triazines,2-(2’-hydroxy-5’-methylpheny1)benzotriazole (I, R = H; trade name Tinuvin P (TIN P)), and d e r i v a t i ~ e s ’ -which ~ ~ * ~are ~ widely used to diminish the photodegradation of polymers. Previous studies demonstrated that in accordance with FBrster’s t h e ~ r y ~excited-state ~-~* intramolecular proton transfer (ESIPT)occurs in the excited singlet state SIfollowed by fluorescence emission with a very large Stokes shift from the proton-transferred S’l ~ t a t e . l -Timeresolved ~~ emission spectrcscopic measurements revealed that proton transfer is faster than a few picoseconds.30 For 2-hydroxyphenyl- 1,3,5-triazines, see refs 23 and 24. Some of the present authors directly measured the protontransfer rate of TIN P from the time dependence of the gain of the stimulated proton-transferred emission (SI So)in fluid CZCl4 at 293 K to be 100 The fluorescence decay time r‘ (S’, S’,) amounts to 150 fs influid CZCl4, whereas approximately 100 ps (141 ps by phase fluorometry,16 90 ps by timeresolved single-photon countingI9) has been found for the neat TIN P crystal (293 K). This underlines the fact that internal vibrations and torsional modes of the molecule are responsible for the extremely rapid and effective radiationless deactivation processes (see also earlier investigations about the temperature dependence of f F and + F / f F ratio, where +F is the overall quantum yield and r ‘ the ~ decay time of the proton-transferred flu~rescence~+~I*”). Blue fluorescence (Amx 39Ol4J5nm, SI So) and phosphorescence (at low temperature)I4J5of TIN P are found in polar
-
-
-
-
-
-
Institut fiir Physikalische Chemic. Institut fiir Organischc Chcmie und Isotopenforschung. 8 Institut fiir Anorganische Chemic. PhysikaIisches Institut. 1 Ciba-Gcigy Ltd. #Present address: Department of Chemistry, University of NebraskaLincoln, Lincoln, NE. *Towhom correspondenceshould be addressed.
solvents where the intramolecular hydrogen bond is broken or when the molecule is distorted by molecular packing forces.32 Methyl TIN (MT, I; R = CH3), in which the hydrogen atom of the ,CH3
R = H, T I N P R = CH,, M T
R-0
I intramolecularhydrogen bond is replaced by CH3 and where the dihedral angles between bonded benzotriazole and pcresol rings are 54.9O and 56.9O (two independent MT mol~ules),~’ also provides blue fluorescence and phosphorescence since no intramolecular proton transfer can take place.14 The distorted molecule without an intramolecular hydrogen bond can no longer be considered a stabilizer (see refs 11, 12, 15, 18, 20, and 21). Dissociation constants and UV and IR absorption spectra of substituted phenols and naphthols (including the benzotriazole substituent) were studied by Durmis et a1.40 In the present paper the influence of substituents at various positions in the substituted phenol ring and in the phenyl ring of the benzotriazole moiety on the molecular structure and the strength of the intramolecular hydrogen bond has bem investigated by X-ray crystal structure analysis, absorption, emission spectroscopy (blue fluorescence, proton-transferredred fluorescence, and phosphorescence), and IR spectroscopy.
Experimental Section Tin P (I, TIN, 2-(2’-hydroxy-5’-methylphenyl)benzotriazole), HM-TIN (2-(3’-tert-butyl-2’-hydroxy-5‘,6’-dimethylphenyl)benzotriazole), HH-TIN (24 2’,4’-dihydroxy-6’-methylphenyl)benzotriazole), DHDTB-TIN (2-(3’,5’-di-tert-butyl-2’,6’-dihydroxyphenyl)benzotriazole), MOHTM-TIN (2-(3’-tert-butyl-2’-hydroxy-5’-methylphenyl)-5-methoxybenzotriazole), HDM-TIN (2-(2’-hydroxy-3’,5’-dimethylphenyl)benzotriazole),
0022-3654/92/2096-10225$03.00/00 1992 American Chemical Society
10226 The Journal of Physicul Chemistry, Vol. 96, No. 25, 1992
HTBM-TIN (2-(3’-tert-butyl-2’-hydroxy-5’-methylphenyl)benzotriazole), CORE-TIN (2-phenylbenzotriazole), H-TIN ((2’-hydroxyphenyl)benzotriazole), HDTB-TIN (TIN 320, 2(3’,5’-di-terr-butyl-2’-hydroxyphenyl)be~~le), BHDTB-TIN (2-(3’,5’-di-tert- butyl-2’-hydroxyphenyl)-5 (a,a’-dimet hylbenzyl)benzotriazole),CI-HTM-TIN (TIN 326,243’-tert-butyl-2’-hydroxy-5’-methylphenyl)-5-chlorobenzotriazole),and MHTM-TIN (2-(3’-tert-butyl-2’-hydroxy-5’-methylpheny1)-5methylbemtriazole) were synthesized at Ciba-Geigy, Fribourg, Switzerland. HM-TIN and HH-TIN were recrystallized from toluene (See Results and Discussion, sections 1 and 2) and the other compounds from n-heptane. See Table V for all formulas. Solvents. 2-Methylbutane (2-MB), n-hexane, n-heptane, and cyclohexane (CH; Merck, Darmstadt, FRG, spectroscopicgrade), methylcyclohexane (MCH; Merck, analytical grade, dried over CaH2and distilled), toluene (dried over Na and distilled), ethanol and methanol (Merck, analytical grade, distilled), dimethyl sulfoxide (DMSO) and CHC13(Merck, spectroscopic grade), and diethyl ether (Merck, analytical grade, dried Over Na, distilled) were used. Solvent mixtures for low-temperature glasses were EPA, diethylether/2-methylbutane/ethanol5/5/2(v) and MCH/2-MB, methylcyclohexane/2-methyIbutane2/1 (v). The absorption spectra in Flgures 9 and 10 were registered with a ZEISS DMR 10,the others with a Perkin-Elmer Lambda 7 UV-Vis absorption spectrometer. Cuvettes made of quadratic quartz tube (Heralux Quarzglas) with a path length of ca. 10 mm were used for emission spectra at low temperature. Fluorescence and phosphorescence spectra corrected for instrumental sensitivity were measured with a spectrometer described previously (meanwhile mi~rocomputerized).’~,~~,~~ For low-temperature experiments see ref 19. Samples in low-temperature glasses were degassed by the usual freezRpumpthaw technique. IR spectra were registered with a Perkin-Elmer PE 457 IR spectrophotometer in an emulsion with Hostaflon. Time-Resdwd EmissioaSpeetroscoW. Picosecond timeresolved fluorescence spectra and transients have been recorded using time-correlated single-photon counting after sync-pumped (and cavity-dumped) laser excitation at 345 nm. The time response (fwhm) of the detection system is approximately 30 ps. Corrections for light intensities and the spectral response of the a p paratus were made. For details see ref 3 1 b. Crystd Structure Determination. X-ray diffraction data from 2-(3’-tert-butyl-2’-hydroxy-5’,6’-dimethylphenyl)~nzotriazole (HM-TIN) were collected on a Syntex PI bar autodiffractometer at room temperature with a 1.5 X 1 .O X 0.75 mm3crystal enclosed in a thin-walled glass capillary. The space group was found to be C2/c for which lattice parameters were determined (by least-squares refinement; with automatically centered 28 values for 25 reflections in the angular range 25.0 I 28 I 55.0’) to be u = 18.439(9)& b = 11.997(4)A, c = 19.302(7)& /3 = 129.55 (0)’; the formula per asymmetric unit is C18H21N30,Z = 8 to Intensities were measured with gragive pale = 1.192 g phitemonochromatizedMo Ka radiation (A = 0.71069A) in an o-scan mode for which the scan range was l.Oo, and the scan speeds varied from 1 .Oo to 29.3’ m i d ; background intensities were measured on each side of the reflection for half the total scan = time. Of the 3403 unique reflections measured [(sin 8/A),,, 0.704A-’],2985were classified as observed [I2 3u(1)]. Data were corrected for variations in the intensities of three check reflections measured periodically and for Lorentz polarization effects but not for absorption (p = 0.707 cm-I). The initial model for the crystal StNctUre was determined by direct methods and developed by difference Fourier and leastsquares Hydrogen atoms were located in difference electron density maps and included in the refinement. All atomic coordinates, anisotropic temperature factors for non-hydrogen atoms, and isotropic temperature factors for hydrogen atoms were refined. The refinement of 283 parameters with 2888 reflections resulted in R = 0.047,R, = 0.074 [w = (U(F,)~ + 0.035F0 10-7(F0)2 10-4(F0)3}-1], and u = 0.982(the estimated standard
-
+
+
Rieker et al. deviation of an observation of unit weight), Diffraction data of 2-(3’-rert-butyl-2’-hydroxy-5’-methylpheny1)benzotriazole (HTBM-TIN) were collected as described above (at room temperature with Mo Ka). The crystal, grown from isopropanol with 0.75 X 0.15 X 0.20 mm3in dimension, was assigned to the orthorhombic space group P212121 with lattice parameters u = 6.201 (2) A, b = 10.529 (3) A,and c = 22.776 (8)A using 25 reflections in the angular range 20° 5 28 5 30’. The formula per asymmetric unit is Cl,H19N30,Z = 4,pale = 1.257 g Intensity data were collected in wscan mode for which the scan range was 0.8’; the scan speed varied from 1.0’ to 29.3’ m i d . 1984 uni ue reflections were measured to the maximum sin @/A of 0.65 1313 reflections were classified as observed [I 2 3u(Z)]. Data were corrected for variations in the intensities of three check reflections, for Lorentz and polarization effects, and for extinction (e = 3.17) but not for absorption (a = 0.750cm-I). The model was determined and refined as described above. The refinement of 267 parameters with 1602 reflections resulted in R = 0.05, R, = 0.046[w = (0.3+ u(FOl2+ 0.0005Fo + 10-8(Fo)2 + 10-8(F0)3)-1], and u = 1.109. Colorless crystals of 2-(2’,4’-dihydroxy-6’-methylphenyl)benzotriazole (HH-TIN), 0.95 X 0.65 X 0.25 mm3, were grown from toluene (dried Over molecular sieves) at room temperature. X-ray diffraction data were measured at 120 K with Mo Ka radiation with a Syntex P1 bar diffractometer (equipped with a Syntex LT-1 low-temperaturedevice) operating in an 0-scan mode. The scan range was 1 .O’; the scan speed varied from l.Oo to 29.3’ min-I; background intensities were measured for one-half the scan time at each side of the reflection. The space group was assigned to Pbcu with lattice parameters u = 7.994 (2)A,b = 9.870(4) A, and c = 30.602(9)A. The formula per asymmetric unit is Cl3HllO2N3~H2O, Z = 8 to give pfalc= 1.427 g c ~ n - ~ . 7436 unique reflections were recorded to (sin €//A), = 0.905; 4778 reflections with Z 1 341)were used. Data were corrected for Lorentz and polarization effects but not for absorption (M = 0.972cm-I). The initial model was determined and developed as described above. The final R factors and weighted R factors were R = 0.051 and R, = 0.067 [w = { U ( F , ) ~ 0.048F0 10-7(~,)2 10-7(~,)3)-q, = 1.069. Colorless crystals of 2-(2’,4’-dihydroxy-6’-methylphenyl)benzotriazole (HH-TIN) were grown from toluene (dried over molecular sieves in addition to azeotropic destillation) at 5 ‘C, yielding a different crystal modification. All X-ray diffraction data were measured at room temperature on a sample with 1 .O X 0.7 X 0.7 mm3in dimensions. Space grou in with lattice parameters u = 7.890 (2)A, b = 7.095 (2) c = 11.761 (2) A; # =I97.94 (2)’ (lattice parameters resulted from refinement with 25 automatically centered 28 values in the range 20-30’; monochromatized Mo Ka radiation was used); the chemical formula per asymmetric unit is C13H1102N3-H20,Z = 2 to give pale = 1.321 g cmV3. Intensity data were measured in an 0-scan mode; the scan rate varied from 1.0’ to 29.3O m i d , and the scan range was 1.0’. Reflections were measured to a resolution of (sin 8/A), = 0.704 A-I. The intensities were currected for systematic decrease in the intensity of three reference reflections and for Lorentz and polarization effects but not for absorption (M = 0.900cm-l). Of the 2042 unique reflections measured, 1349 were classified as observed under the criterion Z 1 3.0u(1). The crystal structure model was determined and developed as described above. A total of 1755 reflections contributed to the refinement of 223 variables to give R = 0.04 and R, = 0.055. The following weighting scheme was used; w = (C(F,)~ + O.OlF, + 10-5(F0)2 + 10-7(F0)3)-1; the estimated standard deviation of an observation of unit weight is 1.177.
2-I;
+
+
+
g
Results and Discrrssion (1) Description of the Crystal Structures. All four structures of 2’-hydroxyphenylbenmtriazole (Tinuvin) derivatives described in this paper show some common features due to their basic composition. For atom labeling and bond distances see Figures
The Journal of Physical Chemistry, Vol. 96, No. 25, 1992 18227
Ultraviolet Stabilizers
1.415
1-146 1.3’49
0
I
1.437
. 362 1.$10
1.371
I533
Figure 1. Atom labeling and bond distances for HTBM-TIN at ca. 293 K. Estimated standard deviations are less than 0.0074 A in bonds between non-hydrogen atoms and less than 0.081 A in those involving H atoms.
\ 1508
Figure 3. Atom labeling and bond distances for HM-TIN at ca. 293 K. Estimated standard deviations are less than 0.0059 A in bonds between non-hydrogen atoms and less than 0.088 A in those involving H atoms.
Figure 4. Stereoscopic projection of the crystal packing of HM-TIN. Figure 2. Stereoscopic projection of the crystal packing of HTBM-TIN.
1,3,5, and 7; coordinates are listed in Tables I-IV. The observed distances demonstrate that the o-quinoid mesomeric form predominates in the benzotriazole moieties as in TIN P,16 whereas the aromatic C-C distances in the substituted phenol rings are nearly equal. The C1-Nl bond between the two ring systems has only slight double bond character. Its distance is nearer to a C-N single bond than to a C-N double bond.37 Furthermore, the two ring systems of the molecules which have a methyl group in position C6 are not planar due to the steric hindrance of this bulky group. Thus no intramolecular hydrogen bond between H(02) and N2 is possible. Instead, we observed intermolecular hydrogen bonds either to another Tinuvin derivative molecule as described in HM-TIN or to a water molecule (as in HH-TIN) which is located such that tetrahedral coordination is possible. 2 4 3’-tert-Butyl-2’-hydroxy-5’-methylphenyl)benzotriazole (HTBM-TIN; see Figure 1) crystallized in a regular arrangement (see Figure 2) without any favored direction. No water or solvent molecules were found in the crystal. There is no bulky group at C6. The dihedral angle between the benzotriazole and phenol ring is 5.1’. The bonding geometry (H(02)-N2 = 1.84 (4) A,
H(02)-02 = 0.81 (5) A, 02-N2 = 2.581 ( 5 ) A, angle 02-H(02)-*N2 = 151 f 4’) is typical for a strong intramolecular hydrogen bond from H(02) to N2, which is also demonstrated by spectroscopic methods, vide infra. The 02-N2 distance is even shorter than the one reported for the parent compound TIN P (2.615 (2) A).16For fractional atomic coordinates see Table I.41 2-( 3’-tert-Butyl-2’- hydroxy-5’,6’-dimethylphenyl)benzotriazole (HM-TIN; see Figure 3), however, shows a different conformation. The dihedral angle between the two ring systems is 89.3’. Therefore, no intramolecular hydrogen bond between H(02) and N2 or N3 exists, indicated by the large H(02)-N3 distance of 2.83 (2) A. The stereoscopic projection of the unit cell (Figure 4) shows the molecules to be packed in pairs. They are linked by two intermolecular hydrogen bonds. Due to the distortion of the bonded benzotriazole and substituted phenol rings and due to the steric hindrance of the voluminous tert-butyl groups, the two HM-TIN molecules forming a pair do not lie one above the other in a planar arrangement. There is an opening angle of 13.9’ .between the two benzotriazole planes of a pair of molecules. The same holds for the planes of the correspondingsubstituted phenol rings. In this case the opening angle is 28.4’. The intermolecular distance of the H atom H(02) is H(02)-N’3 = 2.00 (4) A. The
Rieker et al.
10228 The Journal of Physical Chemistry, Vol. 96, No. 25, 1992 n
P
1
2”” h
I
1.338
1.490
1.i93
1.?76
\
I
1.3184
1.391
I
I
1.3,66
1.3161
Figure 5. Atom labeling and bond distances for HH-TIN (space group Pbca) at ca. 120 K. Estimated standard deviations are less than 0.0019 A in bonds between non-hydrogen atoms and less than 0.027 A in those involving H atoms. I
,
Figure 7. Atom labeling and bond distances for HH-TIN (space group P2,)at ca. 293 K. Estimated standard deviations are less than 0.0157 A in bonds between non-hydrogen atoms and less than 0.049 A in those involving H atoms.
1
Figure 6. Stereoscopic projection of the crystal packing of HH-TIN (space group Pbcu).
prime characterizesthe atom of the other molecule within the pair. All other atoms of significance lie at a distance greater than 3.5 A. It is interesting to note that the distance 02-N’3 (2.800 (3) A) is exactly that given by Pimentel and McClellan3*for hydrogen bonds of the type 0-H--N. There is a nearly linear arrangement of the three partners of the feasible intermolecular hydrogen bond. For fractional atomic coordinates see Table 11. Crystals of 2 42’,4’-dihydroxy-6’-methylphenyl)benzotriazole (HH-TIN; Figure 5 ) were grown at two different temperatures to give two different arrangements. At room temperature they crystallized in the orthorhombic space group Pbca. The dihedral angle between the two ring systems in the molecule is 59.8’ due to the bulky methyl group at C6. There is no specific pair formation in the crystal (Figure 6). The packing of the molecules resembles a “herringbone” arrangement. Both OH groups of the HH-TIN molecule form hydrogen bonds to water molecules (W) in the crystal which have a tetrahedral coordination sphere. The
Figure 8. Stereoscopic projection of the crystal packing of HH-TIN (space group P2,).
distances are: H(02)-0(W) = 1.85 (2) A, H’(04)-O(W) = 1.89 (3) A, Hl(W)-04 = 1.94 (2) A (the prime characterizes the atoms in another asymmetric unit). The intermolecular hydrogen bond of a water molecule W to N2 might have some influence on the molecular packing in the crystal: H2(W)-N2’ = 2.06 (2) A. For the stereoscopic projection see Figure 6, for fractional atomic coordinates see Table 111. Crystals of the same compound (HH-TIN; Figure 7), however grown at 5 ‘C, were assigned to the monoclinic space group ml. There are interesting changes of the molecular and packing geometry due to the reduced temperature and therefore faster crystallization. The dihedral angle between the two ring systems increases to 89.9’ which is similar to 89.3’ for HM-TIN. The molecules, however, lie in a regular arrangement without pair formation (see Figure 8). This difference probably derives from the absence of the voluminous tert-butyl groups (as compared to HM-TIN). As we found for the other HH-TIN conformation water is included in the crystal. In this case, however, hydrogen
The Journal of Physical Chemistry, Vol. 96, No. 25, 1992 10229
Ultraviolet Stabilizers TABLE I: Fractional Atomic Coordinrtes with Estiuuttd Standard DerirW for HTBM-TIN atom X Y Z 0.0977 (1) 0.4780 (3) 0.3051 ( 5 ) N1 0.1202 (1) 0.4157 (6) 0.5755 (3) N2 0.0471 (1) 0.3784 (6) 0.4307 (3) N3 0.1263 (2) 0.4268 (4) 0.1182 (6) c1 0.1814 (2) 0.4717 (4) 0.0543 (6) c2 0.2102 (1) 0.5647 (3) 0.1633 ( 5 ) 02 0.2085 (2) 0.4191 (4) -0,1297 (6) c3 0.2701 (2) 0.4644 (4) -0.2021 (7) C3 1 0.2691 (3) 0.6072 ( 5 ) -0.2505 (9) C32 0.2897 (2) 0.3953 ( 5 ) -0.4088 (8) c33 0.4329 (7) 0.3146 (2) -0.0235 (9) c34 0.3247 (4) 0.1781 (2) -0.2395 (7) c4 0.1231 (2) 0.2806 (4) -0.1778 (6) c5 0.1794 ( 5 ) 0.0920 (2) -0.306 (1) C5 1 0.0978 (2) 0.3325 (4) C6 0.0024 (7) 0.0363 (2) 0.5031 (4) 0.5531 (7) c7 -0.0104 (2) 0.4986 ( 5 ) 0.7031 (8) C8 -0.0095 (2) 0.8681 (8) 0.5829 ( 5 ) c9 0.0364 (2) 0.8924 (8) 0.6732 ( 5 ) c10 0.0818 (2) 0.6791 ( 5 ) 0.7520 (8) c11 0.0813 (2) 0.5926 (4) 0.5767 (7) c12 0.186 (2) 0.594 (4) 0.244 (8) H2 0.637 (4) 0.308 (2) N321 -0.314 (8) 0.262 (2) 0.658 (4) H322 -0.126 (8) 0.239 (2) 0.627 ( 5 ) H323 -0.364 (8) 0.332 (2) 0.415 (4) H331 -0.436 (7) 0.259 (2) 0.413 (4) H332 -0.540 (8) 0.293 (2) 0.303 ( 5 ) -0.383 (8) H333 0.462 (4) 0.350 (2) H341 -0.068 (8) 0.315 (3) H342 0.01 (1) 0.323 (8) 0.304 (2) 0.105 (8) 0.473 ( 5 ) H343 0.195 (1) 0.297 (3) -0.364 (6) H4 0.108 (2) 0.108 ( 5 ) -0.29 (1) H5ll 0.096 (3) 0.193 (6) -0.45 (1) H512 0.051 (3) 0.179 (6) -0.28 (1) H513 0.061 (1) 0.306 (3) 0.044 (6) H6 -0,041 (2) 0.429 (4) 0.697 (8) H8 -0.041 (2) 0.577 ( 5 ) 0.991 (8) H9 0.734 ( 5 ) 0.038 (2) 1.019 (8) H10 0.113 (2) 0.733 (4) 0.766 (7) H11 ~
atom
X -0.02655 (8) -0.0013 (1) -0.07425 (8) -0.0070 (1) 0.0765 (1) 0.13762 (8) 0.0988 (1) 0.1904 (1) 0.2759 (1) 0.1873 (2) 0.2006 (2) 0.0338 (1) -0.0510 (1) -0.1174 (1) -0.0727 (1) -0.1628 (1) -0.08006 (9) -0.1209 (1) -0.1148 (2) -0.0702 (2) -0.0302 (2) -0.0351 (1) 0.108 (2) 0.338 (2) 0.279 (2) 0.275 (2) 0.246 (2) 0.187 (2) 0.120 (3) 0.209 (2) 0.146 (3) 0.254 (2) 0.050 (1) -0.166 (2) -0.132 (3) -0.081 (2) -0.160 (3) -0.183 (3) -0.216 (4) -0.157 (2) -0,145 (2) -0.065 (2) 0.003 (2)
~~~
X/nm
350
b 00
TABLE Ik hctioarl Atomic Coordinate8 with ldnuted Stutdud Dcrirtioa for HM-TIN
250
300
2 00
N1 N2 N3 c1 c2 02 c3 C3 1 C32 c33 c34 c4 c5 C5 1 C6 C6 1 c7 C8 c9 c10 c11 c12 H2 H321 H322 H323 H331 H332 H333 H341 H342 H343 H4 H511 H512 H513 H611 H612 H613 H8 H9 H10 H11
Y
z
0.7894 (1) 0.8660 (1) 0.8248 (1) 0.6731 (1) 0.6307 (1) 0.6980 (1) 0.5185 (1) 0.4670 (2) 0.5303 (2) 0.4699 (3) 0.3448 (2) 0.4567 (1) 0.4980 (1) 0.4211 (2) 0.6100 (1) 0.6626 (2) 0.9355 (1) 1.0184 (2) 1.1247 (2) 1.1507 (2) 1.0728 (2) 0.9609 (1) 0.739 (2) 0.496 (3) 0.525 (3) 0.609 (3) 0.441 (3) 0.547 (3) 0.417 (3) 0.345 (3) 0.296 (3) 0.319 (3) 0.378 (2) 0.399 (3) 0.443 (3) 0.354 (3) 0.745 ( 5 ) 0.640 (3) 0.632 ( 5 ) 0.998 (3) 1.187 (3) 1.230 (3) 1.090 (3)
0.12434 @j 0.0941 (1) 0.15066 (8) 0.12577 (9) 0.20345 (9) 0.27540 (8) 0.20533 (9) 0.2892 (1) 0.3138 (2) 0.3667 (1) 0.2735 (2) 0.1283 (1) 0.0516 (1) -0,0266 (1) 0.04950 (9) -0.0301 (1) 0.1367 (1) 0.1544 (1) 0.1337 (2) 0.0983 (2) 0.0810 (2) 0.1016 (1) 0.285 (2) 0.366 (2) 0.264 (3) 0.327 (2) 0.423 (2) 0.381 (2) 0.343 (2) 0.227 (3) 0.254 (2) 0.331 (2) 0.124 (1) -0.026 (2) -0.077 (3) -0.020 (2) -0.026 (3) -0.087 (3) -0.036 (4) 0.177 (2) 0.142 (2) 0.087 (2) 0.058 (2) Xlnm
450
LOO
350
300
200
250
E
IM.‘cm
15
IO
L.
..I
26
,
30
5
,
, 31
,
,
,
38
, L2
,
,
,
b6 V/cm”
Elgmtt 9. Absorption spectrum of HM-TIN in various solvents (T= 298 K,c = 5 X 10-5 M): ---, methylcyclohexane;-, CHCI,; X-X, EPA; 0-0, McOH/EtOH (1:4 v);
-, DMSO.
bonds were formed between the crystal water molecules and the two hydroxy m ps:H(02)’-0(W) = 1.96 (3) k H’(O4)-O(W) = 1.89 (3) A. In addition, two (weaker) hydrogen bonds to the two nitrogens were found: H2’(W)-N2 = 2.00 (4) A, H1’(W)-N3 = 1.99 (4) A. This hydrogen bond pattern is different from the pattern in space group Pbca, where three oxygens and one nitrogen are
22
26
30
3L
38
L2
L6
0 50=103
Vtcm-‘
Absorption spectrum of HH-TIN in various solvents, (T= 298 K,c = 5 X l r 5 M)---, methylcyclohexane; -, CHCI,; X-X, EPA; 0-0, MeOH/EtOH (1:4 v); -, DMSO. F’igure 10.
involved in the water coordination. The formation of the two crystal types described for HH-TINcan be regarded as an effect of crystallization temperature.
Rieker et al.
10230 The Journal of Physical Chemistry, Vol. 96, No. 25, 1992 TABLE m: F m t i o d A t d c Coordhtea with Estimated Standard Derirtiolls for HH-TIN(h) atom X Y Z 0.13429 (3) 0.5459 (1) 0.6791 (1) N1 N2 N3 c1 c2 02 c3 c4 04 c5 C6 C6 1 c7 C8 c9 c10 c11 c12 H2 H3 H4 H5 H611 H612 H613 H8 H9 H10 H11
ow
H1 W H2 W
0.4370 (1) 0.5797 (1) 0.6328 (1) 0.5407 (1) 0.3716 (1) 0.6247 (1) 0.7981 (1) 0.8762 (1) 0.8890 (1) 0.8071 (1) 0.9070 (2) 0.4853 (1) 0.4700 (2) 0.3677 (2) 0.2805 (2) 0.2903 (2) 0.3965 (1) 0.328 (3) 0.557 (2) 0.984 (3) 1.011 (3) 1.022 (3) 0.917 (3) 0.856 (3) 0.528 (2) 0.357 (2) 0.210 (2) 0.230 (2) 0.1974 (1) 0.250 (3) 0.169 (3)
0.7770 (1) 0.6603 (1) 0.6038 (1) 0.5237 (1) 0.52761 (9) 0.4434 (1) 0.4452 (1) 0.3643 (1) 0.5285 (1) 0.6088 (1) 0.6979 (1) 0.7555 (1) 0.7863 (1) 0.8929 (1) 0.9678 (1) 0.9376 (1) 0.8284 (1) 0.462 (3) 0.387 (2) 0.361 (2) 0.529 (2) 0.707 (2) 0.660 (2) 0.791 (2) 0.735 (2) 0.920 (2) 1.040 (2) 0.987 (2) 0.32105 (9) 0.259 (2) 0.290 (2)
0.12448 (3) 0.17644 (3) 0.10163 (3) 0.07253 (3) 0.07518 (3) 0.04223 (3) 0.04148 (4) 0.01146 (3) 0.06961 (4) 0.10019 (4) 0.13040 (4) 0.19629 (4) 0.24121 (4) 0.25172 (4) 0.21923 (4) 0.17537 (4) 0.16414 (4) 0.0606 (7) 0.0214 (6) 0.0167 (8) 0.0683 (6) 0.1202 (6) 0.1596 (7) 0.1330 (7) 0.2635 (6) 0.2830 (6) 0.2285 (6) 0.1540 (6) 0.04002 (3) 0.0250 (6) 0.0632 (7)
Absorbance
1.2-
1-
0. 0-
0 250
I
0
310
-
-
F i w e 11. Absomtion suectrum of MOHTM-TIN at T = 293 K in EFA,
- (c
5X
M); in MCH/2-MB,
--- ( c
2
X
lW5 M).
Absorbance
(21) Absorptioa Spectra of HM-TIN and HH-TIN in Vanow sahenta Absorption spectra of HM-TIN and HH-TIN in various
-
solvents at 298 K are presented in Figures 9 and 10. There is a shoulder at -333 nm (t 0.64 X lo4cm-’ M-l) and a strong absorption band (e = 1.72 X 104 cm-’ M-l) at 294 nm in the absorption spectrum of HM-TIN in methylcyclohexane (Figure 9). In polar solvents only a short-wavelength band blwshifted to 275 nm (e.g., DMSO) can be detected. Absorption spectra at low temperature in polar solvents do not provide a long wavelength band at -330 nm either. In unpolar solvents such as methylcyclohexane HH-TIN shows a strong maximum at 324 nm (t 2 X lo4 cm-’ M-I) and a weaker shoulder at 288 nm (t 1.4 X lo4 cm-’ MJ, whereas in polar solvents the long-wavelength maximum nearly disappears and the short-wavelength band increases and is blue shifted (ca. 270 nm, DMSO). The absorption spectra at low temperature in polar solvents only slightly differ from the corresponding spectra at room temperature. (In unpolar solvents no low-temperature spectra can be registered because of the low solubility of HHTIN). In earlier papers from our group and others10,14,16,17,19-21 the long-wavelength band has been attributed to an intramolecular CT transition in the planar molecule (with intact intramolecular hydrogen bond, TIN(intra)). In the crystalline state the planar structure of TIN P has been demonstrated by X-ray crystal structure determination.16The short-wavelength absorption band, however, is due to a local transition within the benzotriazole moiety, for both the planar and the distorted (no intramolecular hydrogen bonds) molecule. This interpretation is corroborated by the solvent dependence of the absorption spectrum of TIN P1’ and by the absorption spectrum of MT,14 where the hydrogen atom of the OH group of TIN P is replaced by CH3. In polar solvents some TIN P molecules convert their intramolecular hydrogen bond into an intermolecular one (see also the results of IH NMR = 11.1 ppm, in the polar spectroscopy: TIN P in CDC13 DMSO, however, 6 0 ~ 10.3 ppm). These molecules arc distorted and the intensity of the long-wavelength (CT) band is reduc~2d.I~ According to the X-ray crystal structure determination the dihedral angles between benzotriazole and pcresol rings of MT are
--
Flgore 12. Absorption spectrum of DHDTB at T = 293 K, c M: in EPA, -; in MCH/2-MB, ---.
-
n
5 X lW5
54.9O and 56.3’ (two independent molecules per asymmetric unit).17 In the absorption spectrum of the distorted MT only the short-wavelengthband can be o b s e ~ e d . ’ ~ From the solvent dependence of the absorption spectra of TIN P,I7HTBM-TIN39(see also Table VI), HM-TIN, and HH-TIN, one may conclude that the strength of the intramolecular hydrogen bond is HTBM-TIN > TIN P >> HH-TIN > HM-TIN, which correlates fairly well with the OH vibration frequencies in the IR spectrum (Table V), see also Results and Discussion, section 2.2. In the latter two molecules the CH3 group in the 6’position does not favor a planar arrangement of the molecules. On the other hand, the spectra in unpolar solvents indicate that at least m e of the molecules do not have a dihedral angle between benzotriazole and substituted phenol rings of about 90°. From this one may deduce that the molecular packing and the water content seem to be very important for the geometry of the molecules in the crystal. (2.2) Abeorpth Spectra of Otkr 2 - ( H y d m x y ~ y I ) ~ o triudcs and OH Vibration Frequency (IR Spec-). The absorption spectra of MOHTM-TIN (2-(3’-rerr-butyl-2’-hydroxyS’-methylphenyl)-5-methoxybenzotriazole)and of DHDTB-TIN (243’,5’-di-ferr-butyl-2’,6’-dihydroxyphenyl)benzotriazole)are shown in Figures 1 1 and 12. In the IR spectrum the OH vibration frequency is much lower than that of the free OH group (-3600 an-’)which aloo hdicatm the presence of an intramolecular hydrogen bond; see Table V. Al(Al)/Az(X2) means the ratio of the absorption maxima of the short-wavelength (A,) and the long-wavelength band (A,) in the electronic absorption spectrum. Although there is no strict correlation between the ratio AI(XI)/Az(Az)(e.g., in a solvent mixture
The Journal of Physical Chemistry, Vol. 96,No.25, I992 10231
Ultraviolet Stabilizers TABLE Iv: Fnctiolrrl Atomic Coordi118tea with &tlMted Standard
TABLE V: OH Vlkace Vihtioa in the IR Spcetrurn of
Dcrirtioar for HH-TIN (P2I)
12'-H~droxvpk.~I)bth~oh
atom N1 N3 N2 c1 c2 02 c3 c4 04 c5 C6 C6 1 c7 C8 c9
c1
c11 c12 H2 H3 H4 H5 H611 H612 If613 H8 H9 H10 H11
ow
H1 W H2 W
X 0.9205 (2) 0.9827 (7) 0.9837 (7) 0.8026 (2) 0.8746 (2) 1.0472 (2) 0.7677 (2) 0.5924 (2) 0.4950 (2) 0.5219 (2) 0.6264 (3) 0.5485 (4) 1.0986 (8) 1.208 (1) 1.311 (1) 1.3122 (9) 1.207 (1) 1.0994 (7) 1.072 (4) 0.815 (3) 0.390 (4) 0.400 (3) 0.619 (3) 0.534 (6) 0.450 (5) 1.164 (5) 1.367 (4) 1.422 (4) 1.244 (4) 0.1517 (2) 0.095 (4) 0.117 (5)
Y 0.113 (1) 0.273 (1) -0.042 (1) 0.112 (0) 0.115 (2) 0.114 (1) 0.1 10 (2) 0.116 (1) 0.111 (1) 0.110 (2) 0.116 (1) 0.118 (2) 0.213 (1) 0.310 (1) 0.213 (2) 0.021 (2) -0.085 (1) 0.019 (1) 0.086 (8) 0.073 (4) 0.151 (5) 0.140 (6) 0.065 (4) 0.250 (7) 0.037 (6) 0.447 (6) 0.268 (6) -0.059 (6) -0.216 (6) 0.116 (1) 0.014 (5) 0.204 (6)
z 1.2319 (1) 1.2787 (4) 1.2807 (4) 1.1264 (2) 1.0246 (2) 1.0335 (2) 0.9209 (2) 0.9204 (2) 0.8155 (1) 1.0220 (2) 1.1274 (2) 1.2362 (2) 1.3701 (5) 1.4485 (7) 1.5303 (6) 1.5303 (6) 1.4535 (7) 1.3668 (4) 0.970 (3) 0.850 (2) 0.828 (2) 1.015 (2) 1.297 (2) 1.256 (4) 1.236 (3) 1.468 (3) 1.598 (3) 1.574 (3) 1.427 (3) 0.8203 (1) 0.798 (3) 0.764 (3)
of methylcyclohexane and 2-methylbutane (MCH/2-MB), see Table VI) and i+,H (see Table V), one may conclude that the intramolecular hydrogen bond of MOHTM-TIN is stronger than that of HDM-TIN or TIN P. This is corroborated by the extinction coefficients and their ratios at 293 K for TIN P and MOHTM-TIN in various solvents (see Table VI). The long-wavelength band of MOHTM-TIN is much more intense than the short-wavelength band (Figure 11). In addition the extinction coefficient (ez = 2.9 X 104 cm-I M-', n-hexane) is nearly twice that of TIN P (€2 = 1.63 X 104 cm-' M-', *heptane). This might be due to the strong CT character of the longwavelength absorption band which is considerably strengthened by the OCH3 group in position 5. For TIN P the ratio tl/t2 seriously increases when going from alkane (tl/t2 = 0.85) to DMSO (t,/t2 = 1.89), whereas only small changes are observed for MOHTM-TIN (cI/cz = 0.48,n-hexane; tl/t2 = 0.56, DMSO). This means that DMSO converts the intramolecular hydrogen bond into an intermolecular one to the solvent for a great part of TIN P molecules, whereas this is much less pronounced for MOHTM-TIN. These results, in addition to the IR frequencies (TIN P, 3080 cm-';MOHTM-TIN, 2920 cm-') and the increase of the quantum yield of the proton-transferred fluorescence (S', So),see section 3, underline that the intramolecular hydrogen bond of MOHTM-TIN is stronger than that of TIN P. For phosphorescence, see section 3. Amrding to the IR data (Table V) FoHf q u e n c h of HH-TIN and HM-TIN are highest (PoH = 3415 cm-I for HH-TIN has probably to be attributed to the OH group in 4' position). This corresponds to the nonplanar arrangement in the crystalline state and the comparably weak CT band in the UV absorption spectra (Figures 9 and 10). In this context, however, it should be remembered that EOH refers to the crystalline state (with packing effect,etc.) whereas the UV absorption spectra refer to the 'free" molecule in fluid solution. Therefore, small differences in the geometry of the molecule are feasible under these different conditions. For HH-TIN intermolecular hydrogen bonds to water molecules have been revealed by the X-ray crystal structure determination (see above) which might also contribute to the IR absorption. For HM-TIN intermolecular hydrogen bonds have
-
substance
formula
center of gravity toH/cm-'
HH-TIN
3415 3180
HM-TIN
3140
H-TIN
3130
TIN P
3080
H D M T IN
-
3030
HTBM-TIN
2940
HDTB-TIN (TIN 320)
3070
DHDTB-TIN
3080"
BHDTB-TIN
3170
CI-HTM-TIN (TIN 326)
3080 CI
MHTM-TIN
Value confirmed by measurement of the hydroxy-deuterated compound.
TABLE VI: A i(Xi)/A HDM-TIN HTBM-TIN TIN-P MOHTM-TIN
*(As) md OH
solvent MCHIZ-MB MCH/2-MB n-heptane MCH/Z-MB
Ai1442
1.09 1.05 0.85 0.5 1
PonICm-' 3030 2940 3080 2920
been demonstrated (Resultsand Discussion, section 1). CH3 and tert-butyl substituents in 3' and 5' positions of the substituted phenol ring increase the strength of the intramolecularhydrogen bond (H-TIN, TIN P, HDM-TIN, HDTB-TIN (TIN 320)). By u,u'-dimethylbenzyl and chlorine substituents in the 5 position of the benzotriazole ringH, & is shifted to higher frequencies (HTBM-TIN, BHDTB-TIN, CI-HTM-TIN (TIN 326)), while electron-rich group stabilize the intramolecular hydrogen bond (HTBM-TIN, MHTM-TIN, MOHTM-TIN). It is interesting to note that the short-wavelength band is red shifted (MCH/2-MB) for DHDTB-TIN with two hydroxy in the 2' and 6' positions (see Figure 12). In EPA the longwavelength band is reduced in intensity and only one broad band can be observed. Usually, no large change in the absorbance ratio of the two bands ocwswhen EPA is used instead of MCH/2-MB as solvent. This indicates that despite the presence of two OH
10232 The Journal of Physical Chemistry, Vol. 96, No. 25, 1992
Rieker et al.
TABLE W: Red F b m w w e at 77 K io MCH/ZMB (21, v:v), c = 3 X l o “ M , L = 366nm substance TIN P H-TIN DHDTB-TIN HDM-TIN HTBM-TIN CORE-TIN MOHTM-TIN
h/nm 648
X
500
LOO
20
25
A/,
300
250
I I*
QF
6
c _
900 800700 600
IO4
700 660 662
