J. Phys. Chem. 1981, 85,2047-2050
2047
Micelle-Stabilized Room-Temperature Phosphorescence Characteristics of Carbazole and Related Derivatives Marie Skrilec‘ and L. J. Cilne Love* seton Hall Universlfy, DepaHmnt of Chemlstry, South Orange, New Jersey 07079 (Received: February IO, 198 1; In Final Form: April 15, 1981)
The first report of room-temperature phosphorescence from heterocyclic species dissolved in micellar media is given. The micelle-stabilized room-temperature phosphorescence energies and triplet-state lifetimes of carbazole, N-(2-~yanoethyl)carbazole, N-(2-iodoethyl)carbazole,and N-(2-chloroethyl)carbazolewere observed in mixed-counterion thallium/sodium lauryl sulfate aqueous micellar solution. The lifetimes of these compounds in 77 K ethanol solution and the fluorescence energy maxima of these and other derivatives dissolved in sodium lauryl sulfate, water, and hexane, respectively, are reported. The results are rationalized as a combination of substituent effects, microenvironment polarity, and heavy-atom effect.
Introduction Triplet-state emission has been observed from a large number of carbocyclic compounds at room temperature in aqueous micellar s ~ l u t i o n . ~ Generally, -~ the presence of an internal atom, such as bromine, or an external heavy atom, such as thallium or silver, has been found necessary for efficient intersystem crossing and/or increased radiative T, So deactivation to occur. These pathways are facilitated by a micellar aggregate which can produce a high “effective” concentration of external heavy atoms as well as imposing orientational and positional constraints on the molecular In this manner, micelle-stabilized room-temperature phosphorescence (MS-RTP) has been induced in carbocyclics substituted with functional groups such as amines, aldehydes, carboxylic acids, ketones, halides, e t ~ . ~However, * ~ , ~ there has been no report, to date, of MS-RTP from heterocyclic aromatic molecules. In the present work the micelle-stabilized room-temperature phosphorescence energies, lifetimes, and relative intensities of carbazole and some of its nitrogen-substituted derivatives are detailed. Although low-temperature phosphorescence and solid-substrate room-temperature phosphorescence from carbazole are readily observable and have been studied in detail,&’O the phosphorescence of carbazole(s) in fluid solution and of heterocyclics in micellar solution have not been reported previously. In conjunction with the MS-RTP data, several species derived from carbazole and dicarbazole were studied via low-temperature lifetime data and fluorescence energies to investigate both the internal and external heavy-atom effects and substituent effects at the nitrogen. The species containing an internal heavy atom were found to exhibit a simultaneous internal and external heavy-atom effect resulting in both decreased phosphorescence lifetimes and
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intensities. The effect of solvent polarity on the compound’s fluorescence energy maxima was examined in an attempt to estimate the molecules’ average location in the micellar aggregate. Experimental Section Luminescence spectra were recorded and triplet-state lifetimes were measured with instrumentation described e l ~ e w h e r e . ~ *The ~ J ~spectra are not corrected for instrumental response. Purification of reagents and sample preparation were described elsewhere &O!,~ All carbazoles were synthesized from carbazole and were checked for purity with a Varian MAT high-resolution mass spectrometer and a high-performance liquid chromatography (HPLC) method. All of the compounds studied were >99.5% pure. The solid compounds were dissolved in sodium lauryl sulfate (NaLS) solution and were then diluted with thallium lauryl sulfate/sodium lauryl sulfate (TlLS/NaLS) solution to give a total detergent concentration of 0.10 M with a 30170% ratio of Tl/Na. The compound concentrations for triplet-state lifetime measurements and relative sensitivity determinations were
