Fig. 1. Chemical structure of copper (II) tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin [abbreviated as CuPaz(t-Bu)₄].

Fig. 2. Surface pressure–area isotherm of CuPaz(t-Bu)₄ at the air–water interface at room temperature.

Fig. 3. UV-VIS spectra of CuPaz(t-Bu)₄ in chloroform solution (0.01 mg/ml, curve a) and of 20-layer LB films deposited at 25 (curve b) and 7 mN/m (curve c), respectively.

Fig. 4. Increase in surface density vs. the number of layers for 20- and 50-layer LB films deposited at 25 mN/m.

Fig. 5. UV-VIS spectra of 20-layer CuPaz(t-Bu)₄ LB films without (a) and with the exposure to saturated vapors of benzene (b), toluene (c) and hexane (d).

Fig. 6. Evolution of UV-VIS spectra of 20-layer CuPaz(t-Bu)₄ LB films during the exposure to saturated benzene vapor. The absorbance of UV-VIS spectra of the LB films in response to the saturated benzene vapor is plotted against time of days.

Fig. 7. Response of 20- (dark line) and 50-layer (solid line) CuPaz(t-Bu)₄ LB films during the exposure to alternate 5-min pulses of benzene vapor and clean nitrogen (four cycles). The frequency change was normalized against the vapor concentration. Gas-on stands for the injection of vapor, and gas-off stands for the injection of clean nitrogen. Such normalization and meanings are the same in Fig. 8 and Fig. 9. In this case, the actual gas concentration is 250 ppm.

Fig. 8. Response of 20- (dark line) and 50-layer (solid line) CuPaz(t-Bu)₄ LB films during the exposure to alternate 5-min pulses of toluene vapor and clean nitrogen (four cycles). In this case, the actual gas concentration is 300 ppm.

Fig. 9. Response of 20- (dark line) and 50-layer (solid line) CuPaz(t-Bu)₄ LB films during the exposure to alternate 5-min pulses of hexane vapor and clean nitrogen (four cycles). In this case, the actual gas concentration is 900 ppm.

Fig. 10. Linear decrease in the frequency of QCM crystal coated with CuPaz(t-Bu)₄ LB films vs. the concentration of benzene vapor for 20- and 50-layer films.

Table 1. λ_max and FWHM values of Soret and Q bands of CuPaz(t-Bu)₄ chloroform solution as well as LB films without and with the exposure to various saturated vapors of organic solventsa