A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy‐transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features.

To investigate new architectures for molecular photonics applications, a shape-persistent cyclic hexameric architecture (cyclo-Zn3Fb3U-p/m) has been prepared that is comprised of three free base (Fb) porphyrins and three zinc porphyrins linked at the meso-positions via diphenylethyne units. The synthesis involves the Pd-mediated coupling of a p/p-substituted diethynyl Zn porphyrin and a m/m-substituted diiodo Fb porphyrin, forming p/m-substituted diphenylethyne linkages. The isolated yield of cyclo-Zn3Fb3U-p/m is 5.3% in the presence of a tripyridyl template. The array has C 3 v symmetry, 108 atoms in the shortest path, and a face-to-face distance of ∼35 Å across the cavity. The excited-state lifetime of the Zn porphyrin in cyclo-Zn3Fb3U-p/m is 17 ps, giving a rate of energy transfer to each adjacent Fb porphyrin of k trans = (34 ps)-1 and a quantum efficiency of Φtrans = 99.2%. This rate is comparable to that in a dimer (ZnFbU-p/m) having an identical linker, but slower than that of a p/p-linked ZnFb dimer, which has k trans = (24 ps)-1. At ambient temperatures, the hole/electron hopping rate in [cyclo-Zn6U-p/m]+ is comparable to or faster than the EPR time scale (∼4 MHz). The hole/electron hopping rate in [cyclo-Zn6U-p/m]+ appears to be more than 2-fold larger than for [Zn2U-p/m]+; [Zn2U-p/m]+ has a rate at least 10-fold slower than for the p/p-linked dimer [Zn2U]+. Both excited-state energy transfer and ground-state hole/electron hopping proceed via through-bond mechanisms mediated by the diphenylethyne linker. The origin of the slightly slower energy-transfer rate, and substantially slower ground-state hole/electron hopping rate, in the p/m-linked arrays versus the p/p-linked analogues, is attributed primarily to the larger electron density of the frontier molecular orbitals at the p- versus m-position of the phenyl ring in the diphenylethyne linker. Collectively, these results indicate that the site of attachment of the porphyrin to the linker could be used to direct energy and/or hole/electron flow in a controlled manner among porphyrins in diverse 3-dimensional (linear, cyclic, tubular) architectures.

A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy-transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features.

The redox kinetics for a variety of porphyrin-containing self-assembled monolayers (SAMs) on Au are reported. The measurements probe both the rate of electron-transfer (k 0 ) for oxidation (in the presence of applied potential) and the rate of charge dissipation after the applied potential is disconnected (characterized by a chargeretention half-life (t 1/2 )). The porphyrins include (1) monomeric Zn complexes that contain phenylmethylene linkers wherein the number of methylene spacers varies from 0 to 3, (2) monomeric Zn complexes that contain different ethynylphenyl-derived linkers, and (3) a triple-decker lanthanide sandwich complex with a phenylethynylphenyl linker. The k 0 values for all the porphyrin SAMs are in the range of 10 4 -10 5 s -1 . The k 0 values for the monomeric ethynylphenyl-linked porphyrin SAMs are generally faster than those for the monomeric phenylmethylene-linked SAMs. The rates for the latter SAMs decrease as the number of methylene spacers increases. The rates for the triple-decker SAM are generally slower than those for the monomers. The trends observed in the k 0 values are paralleled in the t 1/2 values, that is, porphyrin SAMs that exhibit relatively faster electron-transfer rates also exhibit faster charge-dissipation rates (shorter t 1/2 values). However, the charge-dissipation rates (no applied potential) are approximately 6 orders of magnitude slower than the electron-transfer rates (applied potential). Both the k 0 and t 1/2 values for the porphyrin SAMs are sensitive to the surface coverage of the molecules. The rates for both processes decrease as the monolayers become more densely packed. This behavior is attributed to exclusion of solvent/counterions and space-charge effects. The effect of surface coverage on rates can overshadow differences that result from differences in linker type/ length. Collectively, the studies help to delineate the molecular design features that could be manipulated to control the redox processes in porphyrin SAMs. The understanding of these processes is essential for the successful implementation of molecules as the active media in information-storage elements.