Optical-limiting effect of polydiacetylenes substituted with heterocyclic group

As a kind of nonlinear optical materials, polydiacetylenes (PDAs) have attracted great attention because of their large third-order susceptibilities, ultrafast responsibilities, and high damage threshold, etc. 5-(2-methylthio-4-methyl)- pyrimidinyl-2,4-pentadiyne-1-ol (PDAA) and its derivatives were synthesized. The optical limiting characteristics of these compounds were demonstrated with nanosecond and picosecond pulses at 532 nm. With linear transmittance as high as 87%, the limiting threshold and limited amplitude of PDATS(PDAA tosylate) were observed to be 200 mJ/cm2 and 150 mJ/cm2 respectively, which are lower than that of C60 with the same high transmittance for visible light. A five-level model describing reverse saturable absorption (RSA) of PDATS was proposed to explain its optical limiting effect. The excited-state absorption cross section and the excited-state lifetime were estimated to be 4.0 multiplied by 10-19 cm2 and 0.6 microseconds respectively.