Light emitting and electrical properties of pure amorphous thin films of organic compounds containing 2-tert-butyl-6-methyl-4H-pyran-4-ylidene

Abstract

Low molecular weight organic compounds which make thin films from organic solutions would be a great benefit in future organic light emitting systems. Two most important advantages should be mentioned. First – repeatability of synthesis of small molecules is better than of polymers. Second – wet casting methods can be applied.In this paper we present optical and opto-electrical properties of three glassy forming compounds containing 2-tert-butyl-6-methyl-4H-pyran-4-ylidene fragment as a backbone. They have the same N,N-dialkylamino electron donating group with attached bulky trityloxyethyl groups. The difference between these compounds is in an electron acceptor group. One has indandione group, second has barbituric acid and third has malononitrile group.Absorption maximum of the compounds is between 470 and 500nm and photoluminescence maximum is between 620 and 670nm. Spectra are red shifted from the weakest acceptor group to the strongest one. Attached bulky trityloxyethyl groups and tert-butyl group decrease interaction between the molecules. This allows obtaining amplified spontaneous emission in pure thin films. The lowest obtained threshold energy was 95μJ/cm2.Electroluminescence efficiency for the system ITO/PEDOT:PSS/Organic compound/BaF/Al was low. For the best compound with malononitrile group it was 0.13cd/A and 0.036lm/W. These compounds most probably could be more suitable as a light emitting dopant in electroluminescence layer.