Near infrared detection by means of coordination complexes

We report on the detection of near infrared (NIR) radiation in the range 900-1600 nm by means of coordination complexes such as [M(RtR'timdt)2]x− (M = Ni, Pd, Pt; R,R'timdt = formally monoreduced disubstituted imidazolidine-2,4,5-trithione; x = 0, 1), and [{Ru(bipy)2}2(μ-L)]x+ (H3L = 9-phenyl-2,3,7-trihydroxy-6-fluorone; x = 1, 3). By exploiting these stable coordination complexes absorbing in the visible and NIR region, the poor stability to air and light usually found in low band-gap organic semiconductors can be overcome. [M(R,R'timdt)2] and [{Ru(bipy)2}2(μ-L)]1+ complexes show π-π* transitions in the range 700-1000 nm, which can be bathochromically shifted by changing their oxidation state. Taking profit of this feature, we prepared photodetecting devices operating in the NIR region up to 1600 nm, thus reaching the appealing spectral range of telecommunications. NIR quantum efficiencies of these preliminary photodetectors, made by simple casting from solution, are comparable to those in the visible of most devices based on pristine organic materials. We succeeded in detecting train pulses with a repetition frequency of about 200 kHz at 960 nm and 80 kHz at 1450 nm, to our knowledge an unprecedented result that demonstrates the possibility to enter the NIR region by organic molecular-based devices.