PHOTOPHYSICS OF A 2,7-DIMETHOXY-N-METHYLCARBAZOLE-BASED POLYSILOXANE

The synthesis, characterization, spectroscopic properties, and photophysics of three poly-(methylsiloxanes) (PMS) labeled with 2,7-dimethoxy-N-methylcarbazole (DMNMC) have been studied in dilute solutions both at room temperature and at 77 K. The chromophoric group has been attached to the polymeric chain through polymethylene spacers (CH2)m, where m = 3, 5, and 6. These polymers differ only in the nature of the spacer, and differential thermal analysis (DTA) has shown that the length of the spacer has a profound influence on the mesogenic properties of these liquid crystalline polymers. The degree of hypochromicity measured in the absorption spectra of these polymers in dilute solutions seems to be correlated to the mesogenic properties of the solid-state polymers as studied by DTA. Time-correlated single-photon-counting measurements were performed on these very dilute solutions of PMS. The decays are in all cases multiexponential at room temperature. This has been attributed to the existence of a distribution of conformations of preformed excimers with an associated spectrum of decay times. However, these traps (excimer sites) are at a relatively low level in dilute solution, making these polymers good candidates for photoconductivity study.