The series of (tert-butyl)catechol-substituted fluorinated naphthalocyanines 1, 2 and 3 displays limiting of the optical power generated with nanosecond light pulses simultaneously at 532 and 1064 nm. Limiting thresholds of 1-3 fall in the range 1.5-2.7 J cm-2 at 532 nm and 2.6-3.7 J cm-2 at 1064 nm when linear transmittance is 0.75 at both wavelengths of analysis. Compared to other unsubstituted naphthalocyanines, 1-3 show a relatively large window of high linear optical transmission between the characteristic Q- and B- absorption bands (above 0.75 for a 250 nm-wide window when 1-3 concentration is in the order of few millimoles per liter in 1 cm thick cells). A general enhancement of photostability in 1-3 is observed for the presence of electron-withdrawing fluorine substituents. The optical limiting effect produced by these systems is evaluated for the protection of optical sensors which operate in both visible and NIR spectral ranges, e.g. the human eye and night vision devices.
The changes that the electrochemical insertion of ions (M equals H, Li or Na) cause in the optical and mechanical properties of electrochromic tungsten bronzes, MxWO3, are reported. The commonly accepted assumption that the electrons and cations have separate effects, namely on the optical properties and film volume (stress), respectively, does not properly describe the results that are obtained with the three different cations. Differences between the cations are explained in terms of cation diffusion in a solid medium. Particular attention is given to the use of the laser beam deflection method, in conjunction with in- situ optical measurements, to characterize electrochromic thin films.
At the moment WO3 is the most suitable material as cathodic film for electrochromic devices, mainly because of its good mechanical and physical properties and efficiency in coloring and bleaching upon cation intercalation. We studied the effect of the electrochemical insertion of small cations (H+, Li+ or Na+) in WO3 thin films by means of `in situ' transmittance and reflectance measurements. As a result we observed for Li+ and Na+ a behavior depending on the cation concentration: under a given limit (around 14 mC/cm2 for a 100 nm thick film) the optical changes were only related to the number of electrons entering the film from the external circuit for the electric charge neutralization. Beside this limit a phase transition was observed with the formation of the so called tungsten bronze and the electrochemical process was no longer reversible. With regard to the intercalation of H+ beside the above mentioned limit the saturation of the optical density was observed, but no bronze formation was detected even for charge insertion as large as 50 mC/cm2. As a consequence, during the insertion of Li+ and Na+ the current density must not exceed a maximum value that also depends on the diffusion of cations inside the film. For the WO3 samples studied during this work we found the diffusion coefficient for Li+ and Na+ to be related to the cation concentration and varying in the range of 10-9 divided by 10-11 cm2/s.