Volume 146, number 3,4 CHEMICAL PHYSICS LETTERS 6 May 1988 VISCOSITY AND MEDIUM EFFECTS ON THE FLUORESCENCE AND PHOTOCHEMICAL BEHAVIOUR OF SOME ARYL CHALCONES El-Zeiny M. EBEID, Mahmood H. ABDEL-KADER, Raafat M. ISSA and Samy A. EL-DALY Department ofchemistry, Faculty ofScience, Tanta University, Tanta, Egypt Received 7 January 1988; in final form 9 February 1988 The emission, excitation and absorption spectra toghether with the fluorescence and photochemical quantum yields of some chalcone derivatives have been studied in organic solvents and micellar and microemulsion media. Both 4-[2-(2-pyri- dyl)ethenyl] (I) and 4- [ 2-( 4pyridyl)ethenyl (11) chalcones show large positive solvatochromic effects. The fluorescence quan- tum yields increase substantially as the medium viscosity increases with a subsequent decrease in the photochemical quatum yield. Compounds I and II undergo excited-state molecular aggregation in concentrated solutions giving excimer-like emission that coincides with emission from crystalline samples. The enthalpies of photoassociation have been estimated. The chalcone derivative I acts as an efficient quencher of the fluorescence of the laser dye 1,Cbis (P-pyridyl-2-vinyl)benzene via a long-range mechanism. The excited-state lifetimes of both I and II are short and at 20°C their 7 values are less than 800 ps. 1. Introduction Several diolefinic derivatives have been used ex- tensively as monomers for solid-state four-center-type photopolymerization [ 1,2], laser dyes [ 3-51 and photographic sensitizing dyes [ 6 1. Acyclic a&unsaturated ketones (chalcones) undergo photodimerization when substituted with aromatic groups in the B-position. In diolefinic chal- cones, photopolymerization occurs on UV irradia- tion of crystalline samples [ 7 1. Little information, however, is available on the fluorescence and pho- tochemical reactivity of these derivatives. The flex- ibility in chalcone diolefinic derivatives is expected to affect their fluorescence characteristics on chang- ing the viscosity of the medium. There is a growing interest in compounds undergoing spectral changes as a result of changing medium viscosities, Such compounds are used as probes of the microenviron- ments in micelles; microemulsions and vesicles [ 8 1. Among the diolefinic systems that exhibit a viscosity effect on emission behaviour is trans- 1,1,4,4-tetra- phenyl-2-methylbutadiene [ 91. In the present communication, we report the in- fluence of the medium on the spectral, photochem- ical and photophysical behaviour of two chalcone derivatives, 4- [ 2- (2-pyridyl)ethenyl] chalcone (I) and 4- [ 2-( 4-pyridyl)ethenyl] chalcone (II). c)cti = +H = CH - ‘-Q (1) zyxwvutsrqponmlkjihgfedcb li_ CH = tH-Q_CH = CH _ ia (II) 2. Experimental Chalcone derivatives I and II were prepared and supplied by Professor Masaki Hasegawa and were used as supplied. Microemulsion solutions were pre- pared using chloroform (oil), water, sodium dode- cyl sulphate (SDS; surfactant) and butanol (co- surfactant ). Water in oil (w/o) microemulsions were prepared by mixing these components in the ratio (by weight) 37.075:4.308:4.308:4.306 respec- tively, and oil in water (o/w) microemulsions by mixing them in the ratio 2.06:43.62: 2.0612.06 respectively. Emission and excitation spectra together with flu- orescence quantum yields ( qS)f and fluorescence age- 0 009-2614/88/$ 03.50 0 Elsevier Science Publishers B.V. ( North-Holland Physics Publishing Division ) 331