Absorptivity and fluorescence properties of 9,10-diiodoanthracene in solutions

Abstract

The molar extinction coefficient, oscillator strength, natural fluorescence lifetime, and fluorescence quantum yield have been determined for 9,10-diiodoanthracene in ethanol at 20 o C. The temperature effect on the quantum yield was studied in the range 120-300 K. The fluorescence lifetime was measured at 77 K. During glassification of ethanol, the fluorescence intensity of 9,10-diiodoanthracene increases by more than 50 times due to the activation nature of the intersystem crossing from the S 1 ( 1 B 2u + ) state. The activation energy and pre-exponential factor for the probability of the intersystem S 1 ( 1 B 2u + ) L T n ( 3 B 3u + )-crossing are found. The long-wavelength shift of the absorption spectrum with increasing bulk polarizability of the solvent is interpreted as evidence of changes in the nonspecific interactions.Introduction. 9,10-Diiodoanthracene (DIA) is one of the least studied halogenated anthracenes. Its synthesis and certain spectral-luminescence properties of its solutions have been reported [1][2][3]. The influence of temperature on absorption spectra in glassified solvents (alcohols) has been investigated [4]. Combination scattering, absorption, and fluorescence spectra of crystals under hydrostatic pressure have been published [5]. Its tendency to undergo photodecomposition, which is especially strong in solvents such as hexane and CCl4, and its low solubility in alcohols create definite experimental difficulties. This probably explains the few publications dedicated to the optical properties of DIA. The basic spectral-luminescence properties of anthracene and its halogenated derivatives are well known and have been reviewed [6,7] and included in handbooks [8]. The goal of our work was to expand the list of anthracenes in tables by adding DIA to them. The investigations are timely because DIA can be used as an effective synthesizer of singlet oxygen. DIA also provides an example of a compound with a clearly evident internal heavy-atom effect. The positions of the absorption and fluorescence bands, the molar extinction coefficient, the fluorescence quantum yield at room temperature, and the fluorescence lifetime at 77 K were obtained directly from measurements and by processing the data. The natural fluorescence lifetime, oscillator strength, and activation energy and pre-exponential factor that characterize intersystem crossing from the S 1 -state were calculated using formulas described in known models.Experimental. Absorption spectra were measured on a Cary 500 spectrophotometer; fluorescence spectra, on a SOLAR SFL-1211A spectrofluorimeter (Minsk). Solutions were not degassed. The quantum yield was determined by a relative method. The standard was a solution of 3,6-diamino-N-methylphthalimide (sublimed) in ethanol with a yield of 0.46 [9]. A custom cryostat stabilized the temperature to within ±1 K as measured by a nichrome-copper thermocouple accurate to ±0.5 K. The fluorescence decay kinetics were measured by correlated photon counting using a TCC900 computer module (Edinburgh Instr...