Optical spectroscopic studies of mononitrated benzo[a]pyrenes.

Spectroscopic properties, including absorption, emission spectra, and excited-state lifetimes of the mononitrated benzo[a]pyrenes (NBaPs), specifically 1-, 3-, and 6-nitrobenzo[a]pyrenes (1-, 3-, and 6-NBaP), are reported, and correlations with structure are developed. With 1- and 3-NBaP, bathochromic shifts are observed in the absorption spectra. The quantum yields of emission display the following trend: BaP >> 6-NBaP > 1-NBaP approximately 3-NBaP.

Photoinduced electron-transfer within osmium(II) and ruthenium(II) bis-terpyridine donor acceptor dyads.

The synthesis and photophysical characterization of two different series of electron donor-acceptor dyads containing Ru(II) and Os(II) bis-terpyridines (M(tpy)(2)(2+)) were prepared and studied in order to compare the oft-studied Ru(tpy)(2)(2+) chromophore with the less studied Os(tpy)(2)(2+) chromophore. The first series of dyads incorporates a benzoquinone (BQ) group as the electron acceptor, whereas the second contains a substituted pyromellitimide (PI) group as the electron acceptor. Steady-state emission experiments indicated efficient quenching of the 3MLCT emission of the electronically excited Os(II)-BQ complexes (7-8) compared to both model complexes (3-4) and the Os(II)-PI complex 10.

Visible-light-driven photoreactions of [(bpy)2Ru(II)L]Cl2 in aqueous solutions (bpy = bipyridine, l = 1,2-bis(4-(4'-methyl)-2,2'-bipyridyl) ethene).

Visible-light-induced photoreactions of [(bpy)2Ru(II)L]Cl2 (bpy = bipyridine, L = trans-1,2-bis(4-(4'-methyl)-2,2'-bipyridyl) ethene) in aqueous solution are examined. From pH titrations, it is found that the Ru complex is a stronger base (pKa* = 6) in the excited state than in the ground state (pKa = 4). Photolysis of the [(bpy)2Ru(II)L] complex in solutions at pH 7 and 12 led to formation of species with increased emission quantum yields, approximately 55 nm blue-shift of the emission maximum to 625 nm, and disappearance of the absorption band at 330 nm, the latter arising from the olefinic bond of the L ligand.

Ultrafast spectroscopy of free-base N-confused tetraphenylporphyrins.

The photophysical characterization of the two tautomers (1e and 1i) of 5,10,15,20-tetraphenyl N-confused free-base porphyrin, as well as the tautomer-locked 2-methyl 5,10,15,20-tetraphenyl N-confused free-base porphyrin, was carried out using a combination of steady state and time-resolved optical techniques. N-Confused porphyrins, alternatively called 2-aza-21-carba-porphyrins or inverted porphyrins, are of great interest for their potential as building blocks in assemblies designed for artificial photosynthesis, and understanding their excited-state properties is paramount to future studies in multicomponent arrays. Femtosecond resolved transient absorption experiments reveal spectra that are similar to those of tetraphenylporphyrin (H2TPP) with either Soret or Q-band excitation, with an extinction coefficient for the major absorbing band of 1e that was about a factor of 5 larger than that of H2TPP.

Efficient synthesis of porphyrin-containing, benzoquinone-terminated, rigid polyphenylene dendrimers.

A series of rigid polyphenylene, free-base porphyrin-containing dendrimers terminated with either dimethoxybenzene or benzoquinone end-groups were prepared by a combined divergent and convergent synthesis. Unlike previous routes for preparing polyphenylene dendrimers that are incompatible with end-groups bearing certain functional moieties, the synthetic methodology chosen for this work enables incorporation of functional groups on the dendrimer end-groups during preparation of the dendrimer wedges and during synthesis of the final dendrimer. The basic strategy utilized a convergent preparation of dendrimer wedges using Suzuki coupling conditions, which were then either attached to a porphyrin core in a divergent coupling step or cyclized to form the porphyrin dendrimer in a convergent step.