Pentacene‐Fused Diporphyrins

Abstract

In this work, we report the synthesis, spectroscopic characterization, and theoretical analysis of a linearly conjugated pentacene-fused porphyrin dimer and cross-conjugated quinone-fused dinaphtho[2,3]porphyrins. These multichromophoric systems display non-typical UV-visible absorptions of either porphyrins or pentacenes/quinones. UV-visible, emission and magnetic circular dichroism (MCD) spectroscopy suggest strong electronic interactions among the multichromophores in the system. DFT calculations revealed the delocalization of the HOMOs and LUMOs spanning the entire dimer and linker assembly. The pentacene-fused porphyrin dimer is significantly more stable than both the corresponding pentacene and the heptacene derivatives. The availability of these huge π-extended and electronically highly interactive multichromophoric systems promises unprecedented electronic and photophysical properties.

Challenging Density Functional Theory Calculations with Hemes and Porphyrins

“…Specifically, the series of bands to the red of 500 nm extending to 750 nm was unusual. Similarly the absorption spectra of the Ni- and Zn- quinone-dinaptho-linked porphyrins (2a and 2b in Ref [ 102 ]; just the Ni-2a complex is shown here) were also unusual but not the same as that measured for the Ni-porphyrin with the pentacene linker (1a).…”

“…The key difference between the two structures is the quinone, located midway in the pentacene ladder in 2a; both are substituted by Ni(II). X-ray diffraction analysis confirmed the ruffling of the quinone-based structure that was predicted by the DFT ground state geometry calculations [ 102 ].…”

“…This brings us then to our last example, which is from the work of Hong Wang and colleagues [ 102 ] that illustrates the value of the computational approach to understanding the optical properties of very large systems. We mean by this that although the computational results might not provide an exact match of the experimental data (of course, solvent effect and solution broadening are not typically obtained from these TDDFT calculations) the energies and electron density distribution in the molecular orbitals can be used to interpret and analyze the optical data, and, particularly, for porphyrins, the respective MCD spectral data.…”

“…TDDFT calculations were carried out on all four of the compounds reported by Jiang et al [ 102 ] Figure 15 shows that clearly for both the Ni-pentacene linker and Ni-quinone-dinaphtho- linker that delocalization is complete especially for the top two filled MOs (for 1a: 501/500; for 2a: 508/507) and the two lowest unoccupied π* orbitals (for 1a: 501/502; for 2a: 509/510). In addition, these MOs are clearly π-ring and pentacene-based.…”

“…However, the assignments of the optical data became clearer when the MCD spectra were compared, Figure 17 . In the Jiang et al [ 102 ] paper, the Ni(II), and free base derivatives of the pentacene-linked diporphyrins (Compound 1a, in Jiang et al . [ 102 ]) and the Ni-, Zn-, and free-base-quinone-dinaphtho-diporphyrins (Compounds 2a, 2b and 2c in [ 102 ]) were reported.…”