The photophysical behavior of 3-chloro-7-methoxy-4-methylcoumarin related to the energy separation of the two lowest-lying singlet excited states Soluble, rigid-rod organometallic polymers trans-͓-Pt(PBu 3 n ) 2 -CwC-R-CwC-͔ ϱ ͑Rvbithienyl 2, terthienyl 3͒ have been synthesized in good yields by the CuI-catalyzed dehydrohalogenation reaction of trans-͓Pt(PBu 3 n ) 2 Cl 2 ͔ with one equivalent of the diterminal alkynyl oligothiophenes H-CwC-R-CwC-H in CH 2 Cl 2 / i Pr 2 NH at room temperature. We report the thermal properties, and the optical absorption, photoluminescence, and photocurrent action spectra of 1 ͑trans-͓ -Pt(PBu 3 n ) 2 -CwC-R-CwC-͔ ϱ , Rvthienyl͒, 2 and 3 as a function of the number of thiophene rings within the bridging ligand. With increasing thiophene content, the optical gap is reduced and the vibronic structure of the singlet emission changes toward that typical for oligothiophenes. We also find the intersystem crossing from the singlet excited state to the triplet excited state to become reduced, while the singlet-triplet energy gap remains unaltered. The latter implies that, in these systems, the T 1 triplet excited state is extended over several thiophene rings. The photoconducting properties do not depend on the size of the thiophene fragment. We discuss and compare our results with studies on oligothiophenes and related organometallic polymers.

Evolution of lowest singlet and triplet excited states with number of thienyl rings in platinum poly-ynesWe present a joint experimental and theoretical investigation of the electronic excitations in transition metal-containing phenylene ethynylenes. The influence of the metal on the nature of the lowest singlet and triplet excited states is characterized. We find that conjugation occurs through the metal sites, which deeply modifies the optical properties of the conjugated chains. We also analyze the chain-length dependence of the singlet-singlet, S 0 →S 1 , singlet-triplet, S 0 →T 1 , and triplet-triplet, T 1 →T n , transition energies; both experimental data and theoretical results indicate that the lowest triplet exciton, T 1 , is strongly localized on a single phenylene ring while the S 1 and T n states extend over a few repeating units. Finally, we estimate the geometric relaxation phenomena occurring in the lowest excited states and perform a Huang-Rhys analysis of the triplet emission spectrum in model systems.

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We have studied the dependence of intersystem crossing and the spatial extent of singlet and triplet excitons in platinum-containing poly-yne polymers with the general formula [Pt(PR3)2C⋮CLC⋮C] n (R = Et, nBu; L = pyridine, phenylene, or thiophene) as a function of electron delocalization in the spacer group L. We also report the synthesis route of those compounds. The optical absorption, photoluminescence, and photoinduced absorption of the corresponding polymers and monomers have been measured. We find that conjugation is increased but intersystem crossing is reduced by the electron-rich thiophene unit, while the opposite occurs for the electron-deficient pyridine unit as compared to the phenylene unit. For all investigated systems, we find that the singlet excited state and a higher lying T n triplet excited state extend over more than a repeat unit while the T1 triplet state remains localized to less then one repeat unit.

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