Journal of Chemical Crystallography, Vol. 29, No. 8, 1999 Crystal structure and luminescence of 2,7-dimethylnaphthalene-1-carbonitrile Laurie A. Brown, (1) Frank R. Fronczek, (1) and Andrew W. Maverick (1)* Received June 24, 1999 The title compound crystallizes in the monoclinic space group P2 1 / c: M r = 181.2; a = 7.119(1), b = 18.389(4), c = 7.5385(6) A ˚ ;  = 91.661(7)°; V = 986.4(5) A ˚ 3 ; and Z = 4. The purified material shows fluorescence similar to other naphthalene derivatives: monomer fluorescence ( max 350-370 nm) in the solid state and in dilute solutions, and excimer fluorescence ( max 421 nm) in concentrated solutions. Intense blue-green luminescence ( max 490 nm) is observed in some partially purified crystalline samples. This is attributed to phosphorescence from two isomeric bromodimethylnaphthalenecarbonitrile impurities detected by GC-MS analysis. KEY WORDS: Fluorescence; dimethylnaphthalene; impurities; phosphorescence. Introduction We have been studying cofacial binuclear bis (- diketone) host complexes and their recognition of guest molecules G (see Scheme 1). 1,2 We have also prepared internally functionalized derivatives such as M 2 (NBA-CN) 2 (see 2). In order to prepare M 2 (NBA- CN) 2 , pure 2,7-dimethylnaphthalene-1-carbonitrile (1-CNU2,7-(CH 3 ) 2 C 10 H 5 ,3) was required. The prepa- ration and X-ray analysis of 3 is presented herein. Scheme 1 Our synthesis of 3 frequently gave an intensely luminescent product. This intense luminescence was found to be due to an impurity which could be sepa- rated from 3 via column chromatography. GC-MS analysis of this luminescent impurity shows that it (1) Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803-1804. *To whom correspondence should be addressed. 961 1074-1542/99/0800-0961$16.00/0  1999 Plenum Publishing Corporation contains two bromo-2,7-dimethylnaphthalenecar- bonitrile isomers. These compounds are believed to be formed from small quantities of dibromo-2,7-di- methylnaphthalene isomers present in the 1-bromo- 2,7-dimethylnaphthalene starting material. Purified 3 shows monomer and excimer fluorescence similar to that previously observed for naphthalene-1-carboni- trile (1-cyanonaphthalene). 3 Experimental Materials were reagent or spectrophotometric grade and were used as received. 1 H and 13 C NMR spectra were recorded by using Bruker AC250 and ARX300 spectrometers. Electronic absorption spec- tra were recorded with use of an Aviv Model 14DS absorption spectrophotometer. Luminescence spec- tra were recorded with solutions degassed by bub- bling with N 2 , using a Spex Industries Fluorolog 2 Model F112X emission spectrophotometer (with a Hamamatsu R636 PMT and an ESCO UG11 colored- glass excitation filter to reduce stray light). The spec- tra were corrected as previously described 4 for varia- tions in detector sensitivity with wavelength. Lumi- nescence lifetime measurements utilized a Nd:YAG laser (355 nm) for excitation, and a Spex 220M mono-