Organic-inorganic hybrids prepared by the sol-gel process are investigated by infrared spectroscopy at room temperature. The matrix of the so-called ureasils is a silica network to which oligopolyoxyethylene chains are grafted by means of urea cross-links. The ureasils preparedsU (2000), U(900), and U(600)sare obtained by reacting three diamines (containing about 40.5, 15.5, and 8.5 oxyethylene units, respectively) with 3-isocyanatepropyltriethoxysilane. The mid-infrared spectra of the diamines are examined. The FTIR spectrum of U (2000) shows that the polyether chains of the parent diamine become less ordered upon incorporation into the inorganic backbone. The assignment of the absorption bands originating from the urea moieties in the ureasils is proposed. Spectroscopic data reveal that the number of oxyethylene units present affects dramatically the amide I and amide II bands and indicate that the N-H groups of the urea linkage are involved in hydrogen bonds of different strength. The existence of non-hydrogen-bonded urea groups and hydrogenbonded urea-urea and urea-polyether associations is suggested. The formation of ureaurea structures is apparently favored in U(600), whereas the number of "free" carbonyl groups is greatest in U(2000).

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Data are reported on the triplet states of a series of fluorene-based A-alt-B type alternating copolymers based on pulse radiolysis-energy transfer and flash photolysis experiments. From the pulse radiolysis experiments, spectra are given for eight copolymers involving phenylene, thiophene, benzothiadiazole, and oligothienylenevinylene groups. Quantum yields for triplet-state formation (PhiT) have been obtained by flash photolysis following laser excitation and in one case by photoacoustic calorimetry. In addition, yields of sensitized formation of singlet oxygen have been determined by time-resolved phosphorescence and are, in general, in excellent agreement with the PhiT values. In all cases, the presence of thiophene units is seen to increase intersystem-crossing quantum yields, probably because of the presence of the heavy sulfur atom. However, with the poly[2,7-(9,9-bis(2'-ethylhexyl)fluorene)-alt-1,4-phenylene] (PFP), thiophene S,S-dioxide (PFTSO2) and benzothiadiazole (F8BT) copolymers, low yields of triplet formation are observed. With three of the copolymers, the energies of the triplet states have been determined. With PFP, the triplet energy is virtually identical to that of poly[2,7-(9,9-bis(2'-ethylhexyl)fluorene)]. In contrast, with fluorene-thiophene copolymers PFaT and PF3T, the triplet energies are closer to those of thiophene oligomers, indicating that there is significant conjugation between fluorene and thiophene units but also that there is a more localized triplet state than with the homopolymers.