2 research outputs found
Tuning Light Absorption in Pyrene: Synthesis and Substitution Effects of Regioisomeric Donor–Acceptor Chromophores
Three isomeric donor–acceptor (DA) chromophores based on pyrene were synthesized to study the effects of substitution pattern on intramolecular charge-transfer absorption through pyrene. These chromophores are nonfluorescent and absorb light in the long-wavelength region approaching 700 nm, making them promising light-harvesters. Their optical properties depend greatly on the substitution pattern of the donor, but their electrochemical properties are relatively unaffected
Pi-Extended Ethynyl 21,23-Dithiaporphyrins: A Synthesis and Comparative Study of Electrochemical, Optical, and Self-Assembling Properties
21,23-Dithiaporphyrins were synthesized
containing pi-extending
ethynyl substituents at the meso positions. These porphyrins displayed
highly bathochromic and broadened absorbance profiles spanning 400–900
nm with molar absorptivities ranging from 2500 to 300,000 M<sup>–1</sup> cm<sup>–1</sup>. Electrochemically, these ethynyl dithiaporphyrins
undergo a single oxidation at 0.44 or 0.57 V and reduction at −1.17
or −1.08 V versus a ferrocene/ferrocenium internal standard
depending on the type of functionalization appended to the ethynyl
group. DFT calculations predict that the delocalization of the frontier
molecular orbitals should expand onto the meso positions of the ethynyl
21,23-dithiaporphyrins; shrinking the HOMO–LUMO energy gap
by destabilizing the HOMO energy. Indeed, the DFT results agree with
our optical and electrochemical assessments. Finally, differential
scanning calorimetry combined with cross-polarized optical microscopy
and powder X-ray diffraction was used to assess the ability of these
porphyrins for long-range order. For the ethynylphenyl alkoxy 21,23-dithiaporphyin,
birefringent, soft-crystalline-like domains were observed by polarized
microscopy, which are marginally sustained by a low-level of crystallinity
detected in the XRD, suggesting that long-range ordering is possible.
Overall, ethynyl 21,23-dithiaporphyrins are able to harvest much lower
energy light and possess lower oxidation and reduction potentials
compared to their pyrrolic analogues, which are desirable properties
for applications in organic electronics