2930
J. Phys. Chem. 1981, 85,2930-2933
dielectric ~0nstant.l~ Since excimer-like arrangements of adjacent molecules are absent in the regular crystal structure, the weak structureless emission observed in crystalline 1 conceivably also could derive from an intramolecular exciplex between the electron-donating anthracene and the electron-withdrawing anthrone. As for the molecular geometry of the ethano-linked anthronylanthracene 2, data of relevance to the folding of the anthrone moiety and its intramolecular proximity to the anthracene have been summarized in Table IV. Because of the extension of the interconnecting chain in comparison to structure 1, the distances between the peri-hydrogen atoms attached to C(6) and C(l0) and the corresponding op osite hydrogen atoms of the anthrone are 3.46 and 3.61 respectively. Intramolecular interactions between the anthrone and the anthracene appear to be negligible. Of the few intermolecular contact distances below 4 A between the two different r systems, all do exceed the 3.55 8,found between O(1) and C(24). Interestingly, a similar bimolecular “head-to-tail-to-head-to-tail” arrangement in the crystal lattice of 1 also leads to a shortest intermolecular distance (3.39 A) between the carbonyl oxygen and C(24). An explanation for the shape and energy of the luminescence spectrum of crystalline 2 was found in the (13) H.-D. Becker and K. Sandros, to be submitted for publication.
results of the molecular packing analysis shown in Figure 4. The interplanar spacing between parallel adjacent anthracene moieties related to each other by inversion symmetry is 3.61 A, and the deviation from perfect overlap is 0.67 A along the long axis and 1.49 A along the short axis of the anthracene. Both the relatively large intermolecular separation by 3.61 A and the large deviation from perfectly overlapping sandwich geometry may contribute to the weak intermolecular a-orbital interaction observed in crystalline 2. The degree of a-orbital overlap appears to be sufficient to cause the loss of fine structure in the emission spectrum, though the luminescence energy of the emission maximum hardly differs from that of the excited state of the anthracene moiety.
Acknowledgment. We thank the Swedish Natural Science Research Council, for grants in partial support of this work, and Drs. F. R. Hewgill, E. Ljungstrom, and L. Sjolin for helpful discussions. Supplementary Material Available: Tables of observed and calculated structure factor amplitudes, anisotropic thermal parameters, hydrogen atom parameters, detailed intermolecular geometries and contacts, and least-squares planes. (Tables SUP-1-9) (26 pages). Ordering information is given on any current masthead page.
Relationship between Fluorescence and Molecular Geometry. The Stereochemistry of 9,lO-Dihydroanthracenes and the Effect of Excimer Geometry on the Emission Spectra of Crystalline Anthracenes Hans-Dleter Becker,*” Kjell Sandros,” Brian W. Skelton,lb and Allan H. White”lb Departments of Organic and Physical Chemistry, Chaimers University of Technology and University of Gothenburg, 5-4 12 96, Guthenburg, Sweden, and the Department ot Physical and Inorganic Chemistry, University of Western Australia, Nediands, Western Austraile 6009 (Received: October 27, 1980; In Final Form: March 2, 198 1)
The structures of the 9-anthrylmethyl-substituted9,10-dihydroanthracenes,derived from 9-anthraldehyde by LiAlH4reduction in tetrahydrofuran, have been analyzed by crystallographicmethods. The two hydrogen atoms in the 9,lO positions are equatorially oriented. Differences in excimer fluorescence energy are attributed to various deviations from perfect sandwich arrangement of parallel adjacent anthracene moieties.
Introduction The reduction of 9-anthraldehyde with lithium aluminum hydride in tetrahydrofuran does not stop at the stage of 9-anthrylmethanol but gives rise to 9-(9-anthrylmethyl)-lO-hydroxymethyl-9,lO-dihydroanthracene, 1. *H NMR (270 MHz) spectroscopic evidence suggested alcohol 1, its acetate, 2, and its benzoate, 3, to be pure isomers, though we were unable to deduce the stereochemistry of the 9,lO-dihydroanthracene moiety.2 In cyclohexane solution, the electronic absorption spectra of 1-3 due to the So-S, transition of the anthracene moiety are perfectly superimposable, the longest-wavelength absorption maximum being exhibited at 391 nm. Likewise, in cyclohexane the fluorescence quantum yield (1) (a) Chalmers University of Technology; (b) University of Western Australia. (2) H.-D. Becker, K. Sandros, and A. Arvidsson, J. Org. Chem., 44, 1336-8 (1979).
1. R = H 2.R = C H, CO 3.R=C6H5C0
of 0.69 is the same for all three compounds, and the emission and absorption spectra show the typical mirror-image relationship. In their crystalline state, however,
0022-3654/81/2085-2930$01.25/00 1981 American Chemical Society
Stereochemistry of 9,lO-Dlhydroanthracenes
t
r
The Journal of Physical Chemistry, Vol. 85, No. 20, 1981 2931
TABLE I: Atomic Fractional Cell Coordinates for Structure 1 (Nonhydrogen Atoms) x/a
0.8027 ( 5 ) 0.6667 (4) 0.6049 ( 5 ) 0.4718 ( 6 ) 0.3894 ( 5 ) 0.4448 ( 4 ) 0.5861 ( 3 ) 0.6466 (3) 0.5601 ( 4 ) 0.7862 ( 3 ) 0.8505 ( 5 ) 0.9879 ( 6 ) 1.0637 (5) 1.0079 (5) 0.8651 ( 3 ) 0.5435 ( 4 ) 0.4423 (3) 0.3018 ( 4 ) 0.2044 (4) 0.2525 ( 5 ) 0.3908 ( 5 ) 0.4874 (4) 0.6403 ( 4 ) 0.6915 (9) 0.8291 (10) 0.6541 (13) 0.6638 (13) 0.7260 (3) 0.8533 (4) 0.9320 (4) 0.8850 (4) 0.7600 ( 4 ) 0.6797 (3)
Figure 1. Corrected emission spectra of crystalllne 1-3.
alcohol 1, acetate, 2, and benzoate 3 give rise to distinctly different emission spectra. Thus, the luminescence of 1, characterized by fine structure and small Stokes shift, is typical of monomer fluorescence of the anthracene fluorophore. The luminescence spectrum of acetate, 2 is structureless and exhibits its maximum at 480 nm. Finally, the broad and structureless crystal fluorescence of 3 has its maximum at 550 nm (see Figure 1). The uniqueness of the seeming “substituent” effect on intermolecular T orbital interactions3 has prompted us to carry out the X-ray analyses of 1-3 reported in this paper.
Crystallography Crystal Data. 1: C&Ia0, M, = 400.5, monoclinic, space group P2’/c (C, 5, No. 14), a = 9.701 (81, b = 12.219 (lo), c = 18.209 (12) p = 93.94 (8)O, U = 2153 (3) A3, D, = 1.23(1), D, = 1.24 g ~ m - 2~ =, 4, F(000) = 848, specimen size 0.41 X 0.30 X 0.21 mm (prism), k~~ = 0.78 cm-l. 2: C32H2602, M , = 442.5, monoclinic, space group C2/c (Czh6,No. 15), a = 25.255 (20), b = 13.139 (12), c = 17.284 (13) A,0 = 124.02 (4)O, U = 4754 (6) A3, D, = 1.23 (l),D, = 1.24 g cm9, 2 = 8, F(000) = 1872, specimen size 0.13 X 0.37 X 0.38 mm (plate), p~~ = 0.76 cm-’. 3: C3,HSO2, M , = 504.6, triclinic, space group PI (Cil, No. 2), a = 16.684 (€9, b = 14.188 (ll),c = 11.985 (9) A, a = 79.41 (6), p = 89.49 (5), y = 78.44 ( 5 ) O , U = 2731 (3) A3, D, = 1.23 (l),D, = 1.23 g ~ m -2~ =, 4, F(000) = 1064, specimen size 0.35 X 0.33 X 0.37 mm (prism), p~~ = 0.90 cm-l. See also Tables 1-111 for atomic fractional cell coordinates. Structure Determination. Data Acquisition. Unique data sets were measured to 28,, 40” (1 and 2) and 45’ (3) on a Syntex P21four-circle diffractometer (monochromatic Mo Ka!radiation, T = 295 (1)K), yielding 2029 (1) 2301 (2) and 6000 (3) independent reflections; of these 1179 (l), 1569 (2) and 3367 (3) with I > 30.(1) were considered “observed” and used in the refinements after solution of the structures by direct methods. Data were not corrected for absorption. Least-squares refinement was basically 9 X 9 block diagonal (C,Othermal parameters anisotropic), but with any hydrogen-atom variables refined in the block of the parent carbon atom; in 2, ( x , y , z , U ) ~could be meaningfully refined, except for the hydrogen atoms of the terminal methyl group which were not sufficiently resolved and were constrained at tetrahedral sites located in difference maps and improved by estimation, while in 1 and
1,
(3) Cf. H.-D. Becker, K. Sandros, B. W. Skelton, and A. H. White, J. Phys. Chem., first of two preceding papers in this issue, and references cited therein.
Y/b 0.9738 (4) 0.9987 ( 3 ) 1.0976 (4) 1.1168 (4) 1.0437 ( 4 ) 0.9506 (3) 0.9237 ( 3 ) 0.8290 (3) 0.7592 (3) 0.8051 (3) 0.7088 (41 0.6853 0.7575 0.8504 0.8807 0.8108 0.7455 0.7595 0.7015 0.6295 0.6149 0.6722 0.6532 0.5493 0.5240 0.4628 0.5374 0.7511 0.7685 0.8586 0.9346 0.9185 0.8264
z/c
-0.2151 (2) - 0.2074 (2)
-0.2375 (2) - 0.2307 (2)
-0.1956 ( 2 ) -0.1647 ( 2 ) -0.1679 ( 2 ) -0.1348 (2) - 0.0875 ( 2 ) -0.1447 (2) -0.1161 ( 3 ) -0.1260 (3) -0.1655 ( 3 ) -0.1951 ( 3 ) -0.1869 ( 2 ) -0.0102 (2) 0.0314 (2) 0.0156 ( 2 ) 0.0531 (2) 0.1076 (2) 0.1239 ( 2 ) 0.0855 ( 2 ) 0.1039 (2) 0.0680 (5) 0.0764 ( 6 ) 0.0855 ( 5 ) 0.0122 ( 7 ) 0.0863 ( 2 ) 0.1256 ( 2 ) 0.1130 (2) 0.0619 ( 2 ) 0.0220 (2) 0.0337 ( 2 )
TABLE 11: Atomic Fractional Cell Coordinates for Structure 2 atom c(2j CI 3)
o(221j C(2221
x/a
0.8268 ( 2 ) 0.7619 (1) 0.7213 (2) 0.6581 (2) 0.6298’(2) 0.6665’(2) 0.7346 (1) 0.7737 (1) 0.7444 ( 2 ) 0.8402 (1) 0.8837 (1) 0.9475 ( 2 ) 0.9732 ( 2 ) 0.9344 (2) 0.8670 (1) 0.7359 (1) 0.6984 (1) 0.6321 ( 2 ) 0.5963 ( 2 ) 0.6278 ( 2 ) 0.6931 ( 2 ) 0.7290 (1) 0.8009 (1) 0.8248 ( 2 ) 0.8937 (1) 0.9254 (1) 0.9002 (1) 0.9954 ( 2 ) 0.8312 (1) 0.8914 ( 2 ) 0.91 96 ( 2 ) 0.8874 ( 2 ) 0.8277 ( 2 ) 0.7992 (1)
Y/b 0.9126 (3) 0.9147 (2) 0.9712 (3) 0.9750 (3) 0.9211 ( 3 ) 0.8673 ( 2 ) 0.8611 ( 2 ) 0.8058 (2) 0.7537 (3) 0.8027 ( 2 ) 0.7469 (3) 0.7478 ( 3 ) 0.8039 (3) 0.8577 (3) 0.8588 ( 2 ) 0.8233 ( 2 ) 0.7679 ( 2 ) 0.7633 ( 3 ) 0.7083 (3) 0.6576 ( 3 ) 0.6625 ( 3 ) 0.7165 ( 2 j 0.7172 (21 0.6164 ( 3 j 0.6118 (2) 0.5490 (2) 0.4983 (2) 0.5513 ( 3 ) 0.8088 ( 2 ) 0.8424 (3) 0.9268 ( 3 ) 0.9798 ( 3 ) 0.9486 ( 2 ) 0.8618 ( 2 )
z/c
0.0788 (2) 0.0152 (2) 0.0331 (2) -0.0297 ( 3 ) -0.1142 ( 2 ) - 0.1343 (2) -0.0707 ( 2 ) - 0.0903 (2) -0.1829 ( 2 ) -0.0230 ( 2 ) - 0.0351 ( 2 ) 0.0305 ( 3 ) 0.1132 ( 3 ) 0.1287 (3) 0.0624 ( 2 ) -0.2626 ( 2 ) -0.3543 ( 2 ) - 0.4042 ( 2 ) -0.4864 (2) -0.5190 ( 2 ) -0.4720 (2) -0.3890 ( 2 ) -0.3358 ( 2 ) - 0.2828 ( 3 ) -0.2355 (1) -0.1629 ( 2 ) -0.1351 ( 2 ) -0.1223 (3) - 0.2730 ( 2 ) -0.2474 ( 2 ) -0.1911 ( 2 ) -0.1609 ( 3 ) -0.1864 ( 2 ) -0.2408 ( 2 )
3, this was only possible for (x,Y,z)~,UH being constrained at 1.25(U, (parent C)), Residuals at convergence were (1,
2932
The Journal of Physical Chemistry, Vol. 85, No. 20, 1981
Becker et al.
TABLE 111: Atomic Fractional Cell Coordinates for Structure 3 atom C(1001) C(1002) C(1003) C(1004) C(1005) C( 1006) C(1007) C( 1008) C( 1081) C(1009) C(1010) C(1011) C( 1012) C(1013) C(1014) C(1015) C( 1016) C(1017) C(1018) C(1019) C( 1020) C( 1021) C(1022) C(1221) O(1221) C( 2222) O(1222) C( 1223) C( 1224) C( 1225) C( 1226) C( 1227) C( 1228) C(1023) C( 1024) C( 1025) C( 1026) C(1027) C( 1028)
x/a
0.5615 (5) 0.5619 ( 2 ) 0.5306 ( 3 ) 0.5299 ( 3 ) 0.5603 ( 3 ) 0.5910 (2) 0.5929 ( 2 ) 0.6228 ( 2 ) 0.6561 ( 2 ) 0.6224 ( 2 ) 0.6519 (2) 0.6500 ( 3 ) 0.6183 ( 3 ) 0.5905 ( 3 ) 0.5910 ( 2 ) 0.7456 ( 2 ) 0.7678 ( 2 ) 0.7422 ( 2 ) 0.7617 ( 3 ) 0.8075 ( 3 ) 0.8335 ( 3 ) 0.8148 ( 2 ) 0.8429 ( 2 ) 0.7811 ( 3 ) 0.8131 (1) 0.7611 ( 2 ) 0.6889 ( 2 ) 0.7980 ( 2 ) 0.8797 (2) 0.9134 ( 3 ) 0.8641 ( 3 ) 0.7837 ( 3 ) 0.7490 (3) 0.8550 (2) 0.9122 ( 2 ) 0.9228 ( 3 ) 0.8766 ( 2 ) 0.8196 ( 2 ) 0.8074 ( 2 )
y/b 1.1573 ( 3 ) 1.0775 (3) 1.0890 ( 4 ) 1.0117 (4) 0.9150 ( 4 ) 0.8998 (3) 0.9794 ( 2 ) 0.9669 ( 2 ) 0.8650 ( 3 ) 1.0497 ( 2 ) 1.0441 ( 3 ) 1.1247 (3) 1.2180 ( 3 ) 1.2298 (3) 1.1463 (3) 0.8209 ( 2 ) 0.7137 ( 2 ) 0.6435 ( 3 ) 0.5457 ( 3 ) 0.5158 ( 3 ) 0.5838 (3) 0.6829 ( 2 ) 0.7568 (3) 0.7820 ( 3 ) 0.8450 (2) 0.8959 (3) 0.8946 (2) 0.9531 ( 2 ) 0.9575 (3) 1.0083 ( 3 ) 1.0551 (3) 1.0520 (3) 1.0013 ( 3 ) 0.8466 ( 2 ) 0.9000 ( 3 ) 0.9827 ( 3 ) 1.0135 ( 3 ) 0.961 1 (3) 0.8777 (2)
z/c
0.4039 (3) 0.3516 (3) 0.2391 (4) 0.1899 (4) 0.2487 (3) 0.3579 ( 3 ) 0.4137 (3) 0.5256 (3) 0.5912 (3) 0.5760 (3) 0.6882 (3) 0.7350 (4) 0.6725 (4) 0.5662 (4) 0.5127 (3) 0.5619 (3) 0.6161 (3) 0.5658 (3) 0.6131 (4) 0.7127 (4) 0.7639 (3) 0.7169 (3) 0.7745 (3) 0.8650 (3) 0.9283 (2) 0.9891 (3) 0.9875 ( 3 ) 1.0576 ( 3 ) 1.0516 (3) 1.1206 (3) 1.1959 ( 3 ) 1.2016 (3) 1.1333 ( 3 ) 0.6914 (3) 0.7142 (3) 0.6401 (3) 0.5408 (3) 0.5170 (3) 0.5914 (2)
2, 3) R = 0.036, 0.037, 0.039; R‘ = 0.043, 0.044, 0.046. Reflection weights were (a2(Fo) 0.0005(F0)2)-1.Neutral atom scattering factors were used throughout, C,O corrected for anomalous dispersion (f‘,f’’).4-6 Computation was carried out by using a local variant of the X-RAY 76 program system’ implemented on a Cyber 73 computer. Carbon-atom numbering is as above; oxygen- and hydrogen-atom numbering follows that of the parent carbon, suffixed A and B where needful for distinguishing purposes. Where necessary the two independent molecules in 3 are prefixed 1,2. Abnormal features: the terminal -CH20H group in 1 was found to be disordered over three sets of sites and was modeled in the refinement by three oxygen atoms (population 0.33 each) with associated hydrogen atoms (CH2, OH) estimated and constrained. Additional data are available as supplementary material. (See paragraph at end of text regarding supplementary material.)
+
Results and Discussion The X-ray structure analyses of 1-3 reveal that the two nonaromatic hydrogen atoms of the dihydroanthracene moiety are in equatorial position. Thus, most likely for steric reasons, the two carbon substituents of the di~~
~
~
(4) D. T. Cromer and J. B. Mann, Acta Crystallogr., Sect. A, 24,321
(1968). (5) D. T. Cromer and D. Liberman, J. Chern. Phys., 53,1891 (1970). (6) R. F. Stewart,E. R. Davidson, and W. T. Simpson, J.Chern. Phys., 42, 3175 (1965). (7) J. M. Stewart,Ed., “The X-RAY System-Version of March, 1976”, Technical Report TR-446,. Computer Science Center, University of Maryland, College Park, MD.
atom
x/a
c(2001)
0.4640 ( 2 ) 0.4698 ( 2 ) 0.4046 ( 2 ) 0.4106 ( 3 ) 0.4832 ( 2 ) 0.5466 ( 2 ) 0.5432 (2) 0.6082 (2) 0.6866 ( 2 ) 0.5995 ( 2 ) 0.6614 ( 2 ) 0.6523 ( 3 ) 0.5813 ( 3 ) 0.5211 (3) 0.5263 ( 2 ) 0.7441 (2) 0.8094 ( 2 ) 0.7899 ( 2 ) 0.8488 (3) 0.9264 ( 3 ) 0.9461 ( 2 ) 0.8887 ( 2 ) 0.9109 (2) 0.9044 ( 3 ) 0.9270 (1) 0.8852 ( 2 ) 0.8303 ( 2 ) 0.9070 (2) 0.9677 ( 3 ) 0.9865 ( 3 ) 0.9468 ( 3 ) 0.8873 (3) 0.8659 (3) 0.8585 ( 2 ) 0.8908 (3) 0.8453 (3) 0.7685 (3) 0.7364 ( 2 ) 0.7807 ( 2 )
C( 2002) C( 2003) C( 2004) C( 2005) C( 2006) C( 2007) C( 2008) C( 2081) C( 2009) C( 2010) C( 2011) C( 2012) C( 2013) C( 2014) C(2015) C( 201 6) C( 2017) C( 2018) C( 2019) C( 2020) C( 2021) C( 2022) C( 2221) O( 2221) C(2222) O(2222) C( 2223) C( 2224) C( 2225) C( 2226) C( 2227) C( 2228) C( 2023) C( 2024) C( 2025) C( 2026) C( 2027) C( 2028)
Y/b 0.4405 (3) 0.3887 (2) 0.3456 ( 3 ) 0.2951 (3) 0.2822 ( 3 ) 0.3221 (3) 0.3779 ( 2 ) 0.4209 (2) 0.4042 (2) 0.4756 (2) 0.5233 (3) 0.5741 ( 3 ) 0.5807 (4) 0.5381 (3) 0.4839 (2) 0.3040 (2) 0.2768 ( 2 ) 0.2343 ( 3 ) 0.2088 (3) 0.2229 (3) 0.2632 (3) 0.2902 (2) 0.3370 ( 3 ) 0.4458 (3) 0.4938 ( 2 ) 0.5818 (3) 0.6216 (2) 0.6267 ( 2 ) 0.5796 (3) 0.6264 (3) 0.7189 (3) 0.7662 (3) 0.7211 (3) 0.3187 (2) 0.3154 (3) 0.2959 (3) 0.2781 ( 3 ) 0.2806 ( 3 ) 0.3017 (2)
z/c
0.2264 0.1386 0.1086 0.0247 -0.0379 -0.0126 0.0754 0.1018 0.0377 0.1894 0.2198 0.3062 0.3688 0.3451 0.2532 0.0863 0.0031 - 0.0866 -0.1634 -0.1518 -0.0631 0.0161 0.1113 0.0646 0.1529 0.1565 0.0885 0.2503 0.3297 0.4139 0.4204 0.3417 0.2570 0.2135 0.3220 0.4172 0.4064 0.2999 0.2022
(3) (3) (4) (4) (3) (3) (3) (3) (3) (3) (3) (4) (4) (4) (3) (3) (3) (3) (3) (4) (3) (3) (3) (3) (2) (3) (3) (3) (3) (4) (3) (3) (3) (3) (3) (3) (3) (3) (3)
TABLE IV: Geometrical Features of the 9,lO-Dihydroanthracene Moieties in Structures 1-3 1 ~
2
3
~
Interplanar Dihedral Angles (deg) D-D’ 151 154 E-C( 15)’ 23 25 E-C( 22)‘ 22 21 ABC-C 23 10 ABC-D’ 42 14 ABC-C( 15)b 13 4 C( 15)-C( 8 )
150 22 26 16 44 9
Torsion Angles (deg) 60 56
‘The plane of E was defined by C( 16), C( 21), C( 23), and C( 28). The plane of C( 1 5 ) was defined by C( 15), C( 16), and C( 28); that of C( 22) was defined by C( 21), C( 22), and This angle is that between the plane of the C( 23). anthracene and that defined by C( a), C( 81), and C( 15). hydroanthracene assume axial positions. Other characteristic features of relevance to the dihydroanthracene geometry, such as the angle (-150’) between rings D and D’, or the folding of the hydroaromatic ring E (-25O) are summarized for the three compounds in Table IV. Among the parameters of molecular geometry, the most outstanding is the distance of 1.56 A, that of the single bond between the dihydroanthracene and the 9-anthrylmethyl moiety (C(15)-C(Bl)). Since the “opposite” dihydroanthrylmethyl bond C(22)-C(221) is only 1.45 A, electronic interaction* by the surrounding T systems may (8) Cf. H.-D. Becker, K. Sandros, B. W. Skelton, and A. H. White, J . Phys. Chern., second of two preceding papers in this issue.
Stereochemistry of 9,lO-Dihydroanthracenes
The Journal of Physical Chemistty, Vol. 85, No. 20, 1981 2933
a
c-
Flgure 2. Unit-cell contents of 1 projected down b . Nonhydrogen atoms only are shown (as 20% thermal ellipsoids) together with atom numbering. (The labeled molecule lles at ( x , y , l + z ) . )
L
b sin&
Flgure 4. Unit-cell contents of 3 projected down c.
TABLE V: Deviations from Perfectly Overlapping Anthracene Moieties by Shifts (in A ) along the Long ( a ) and Short ( b ) Anthracene Axes interplanar a b separation structure 1.09 3.46 2 1.48 3 1.18 1.16 3.49
Figure 3. Unit-cell contents of 2 projected down b . (The labeled molecule lies at ( x , y , l + z ) . )
be a factor contributing to the C(8)-C(15) bond elongation. Because of mutual steric repulsion of the “inner” perihydrogen atoms of the anthracene and the dihydroanthracene moieties in a quasi-symmetrical alignment shown in Figure 2, the two ring systems evade each other by rotation around the 9-anthrylmethyl bond C(8)-C(81) and concomitant rotation around the elongated dihydroanthrylmethyl bond C(15)-C(81). Compared to acetate 2 the molecular geometry of alcohol 1 is characterized by slightly larger angles of rotation (cf. Table IV). The variations in intramolecular geometry may be small, however, their relation to the intermolelcular packing patterns appears to be significant. Thus, in the crystal lattice of alcohol 1, anthracene moieties of adjacent molecules along the crystallographic b axis are separated by
-6 A, the angle between the two anthracene planes being 59.0”. As a result of negligible intermolecular .rr-orbital interaction, the fluorescence spectrum of crystalline 1 resembles, in fine structure and energy, that of 1 in dilute solution. Parallel adjacent anthracene moieties in the structure of acetate 2, stacked along the crystallographic b axis, are separated by an interplanar distance of 3.46 8, (see Figure 3). In the case of benzoate 3, parallel overlapping anthracene planes of adjacent molecules are separated by 3.49 A (see Figure 4). This difference in interplanar separation indeed is small and hardly explains the difference in the degree of ?r-orbital interaction reflected in the crystal luminescence energy of acetate 2 and benzoate 3. However, the pairwise arrangements of anthracene moieties in the crystal lattice of 2 and of 3 differ more significantly in their deviation from a perfectly overlapping sandwich structure. In both cases, the parallel adjacent anthracene planes are offset along the axes of the aromatic hydrocarbon, as summarized in Table V. The large shift by 1.48 A along the long axis of the anthracene moiety of acetate 2 is probably responsible for the decrease of intermolecular ?r-orbital interaction evidenced by the higher excimer emission energy in comparison to that of benzoate 3.
Acknowledgment. We thank the Swedish Natural Science Research Council, for grants in partial support of this work, and Drs. F. R. Hewgill, E. Ljungstrom, and L. Sjolin for helpful discussions. Supplementary Material Available: Tables of observed calculated structure factor amplitudes, anisotropic thermal parameters, hydrogen atom parameters, detailed intermolecular geometries and contacts, and least-squares planes (Tables SUP-1-15) (54 pages). Ordering information is given on any current masthead page.
