| Abstract [eng] |
Organic luminophores are widely used as active materials in various optoelectronic devices including organic light-emitting diodes (OLEDs) and optical sensors. Further generation of organic luminophores with enhanced or even unique properties can predictively leads to improvement efficiency of known optoelectronic devices or even to discovery of novel devices. Newly designed and synthesised derivatives of 5,5-dioxi-phenothiazine, benzophenone and sulfonyldi-4,1-phenylene, bis[4-(5,5-dioxo-10H-phenothiazin-10-yk)phenyl]methanone (compound 1) and 10,10'-(sulfonyldi-4,1-phenylene)bis-10H-phenothiazine-5,5-dioxide (compound 2) were selected for this study aiming to find their most appropriate applications in optoelectronic devices. With such propose, photophysical properties of compounds 1 and 2 in different media were provided using various spectroscopic techniques, such as photoluminescence spectra measurement at different temperature and time-resolved fluorescence spectroscopy. Both materials emitted blue light under UV excitation in low-polarity solutions and solid-state film. Moreover, those materials were characterised by thermally activated delayed fluorescence which allows harvesting of both singlet and triplet excitons in OLEDs under electrical excitation required for 100% of internal quantum efficiency of such devices. When compounds 1 and 2 were used as emitting layer in OLEDs, the fabricated devices showed maximum external quantum efficiency (EQE) up to 1.2%. Such relatively low EQE is related to low photoluminescent quantum yield (up to 9.3%) of the studied compounds in solid films. Fortunately, compound 1 showed external stimuli responsive fluorescence behaviour being good for optical sensors. Intensity enhancements (up to 83 times) and colour high-energy shifts (in the range of CIE coordinates from (0.29; 0.45) to (0.17; 0.16)) were detected for solutions of compounds 1 under different doses of UV excitation. Due to the best of our knowledge, such phenomenon was first time observed here for acceptor*-acceptor-acceptor*type organic luminophores. Such fluorescence behaviour of compound 1 is most probably attributed to its conformational changes under external stimuli. It was demonstrated that detected properties of compounds 1 can be useful for its unique applications in ultraviolet radiation dosimeters. Under UV power in the range of 0-350 μW, DMF solutions of compound 1 showed linear UV response with slope of 115500 (R2=0.93) demonstrating very high UV sensitivity. |
