We present a joint experimental and theoretical investigation of the linear and nonlinear optical response of butadiyne-linked zinc porphyrin oligomers. Efficient overlap between the chromophores leads to a large red-shift of the Q absorption band together with a splitting of the B band into two components when increasing the chain length from one to two repeating porphyrin units. Ultrafast pumb-probe measurements performed on these compounds show several well-defined features, associated with singlet excited state absorption. We also find clear evidence for the formation of longer-lived triplet excitons, resulting from very efficient singlet-triplet intersystem crossing processes. For the monomers, the assignment of the observed linear and photoinduced absorption features is supported by a Configuration Interaction description of the singlet and triplet excited states. In the case of the porphyrin dimer, agreement with the experimental results can only be obtained by considering a sizable cumulenic contribution in the excited-state geometry used as input for the CI calculations. The potential of porphyrin systems for Reverse Saturable Absorption and Nonlinear Optics is emphasized.
Communications
ADVANCED MATERIALS Fig. 3. Powder X-ray diffraction data for the palbadiUm-Siher alloy film deposited at a preheating temperature of 80°C and substrate temperature of 250 "C on an SiO, substrate. The lines marked "0" and " " are at the 20 positions of authentic. crystalline Ag and Pd, respectively. Peaks marked "*" are due to the Ag/Pd film; all other peaks are derived from the substrate. grain sizes of 0.1 -0.2 pm and were deposited at a deposition rate of 230 Ajmin. X-ray powder diffraction data showed the presence of CuPd alloy together with (1 11) oriented Cu as expected based on the binary alloy phase diagram.[221 Silver-copper alloy films were deposited under the same conditions with a deposition rate of approximately 180 A/ min. Powder X-ray diffraction data show the presence of Ag/Cu alloy with a (1 11) preferential orientation consistent with the binary alloy phase diagram.[22]In summary, the AACVD of crystalline silver, palladium and binary metal alloys of Pd/Ag, Pd/Cu and Ag/Cu has been demonstrated. Aerosol-assisted CVD has the following potential advantages over traditional precursor delivery methods: (i) higher deposition rates, (ii) transport of thermally sensitive compounds and (iii) reproducible deposition of binary materials. The generality of this technique for other metals and a quantitative description of the deposition of binary metal alloys is being investigated.
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