Dendrimers Made of Porphyrin Cores and Carbazole Chromophores as Peripheral Units. Absorption Spectra, Luminescence Properties, and Oxidation Behavior

Abstract

Luminescent and redox-active porphyrin-based dendrimers of first and second generation have been synthesized, and their absorption spectra, photophysical properties, and oxidation behavior have been investigated, together with those of the corresponding aldehyde carbazole precursors. All the dendrimers contain a porphyrin core and carbazole-based chromophores as branches. The structural formulas of the new species are represented in Figures 1 and 2, with the corresponding schematizations. The absorption spectra of the aldehyde carbazole precursors A1-A6 in dichloromethane exhibit intense transitions in the UV region, centered on the carbazole and benzaldehyde subunits. The lowest-energy absorption bands receive contribution from charge-transfer transitions. Compounds A1-A6 are luminescent at room temperature in fluid solution; such a luminescence is attributed to twisted intramolecular charge-transfer excited states. The luminescence at 77 K in a rigid matrix is blue-shifted with respect to room-temperature emission and is assigned to locally excited states. Absorption spectra of the porphyrin-cored dendrimers P1-P6 appear additive as they are constituted by visible bands due to porphyrin absorption and bands in the UV region due to transitions centered on the carbazole-based branches. Emission spectra of P1-P6 both at 77 K and at room temperature are typical of porphyrin species and independent of excitation wavelength, indicating that the light collected by the peripheral chromophores is quantitatively transferred to the core. All the compounds exhibit a rich oxidation behavior in 1,2-dichloroethane solution, with reversible processes centered on the different carbazole subunits. Interaction between the different carbazole centers depends on the size of the spacer interposed.

Selective Tuning of the HOMO–LUMO Gap of Carbazole‐Based Donor–Acceptor–Donor Compounds toward Different Emission Colors

“…As such, twisted intramolecular chargetransfer (TICT) excited states and luminescence might be observed for 3 and 4. [23] This is true and supported by the following results: [24] (i) The large Stoke shifts of ca. 7059 and 5748 cm -1 for 3 and 4, respectively.…”

Creating a Molecular‐scale Graded Electronic Profile in a Single Polymer to Facilitate Hole Injection for Efficient Blue Electroluminescence

“…The absorption maxima of all poly-spiros as a solid film are nearly identical (at 385-388 nm) because of the non-conjugated linkage between charge transport moieties and the main chain. The additional absorption peaks at 350 and 300 nm for poly-spiros grafted with hole-transporting moieties are attributed to the absorptions of TPA [15] and Cz [16] moieties. The above observation reveals that the modifications of poly-spiros do not alter the photoluminescence (PL) and electroluminescence (EL) spectra significantly (peak maxima at $420 nm, which is similar to polyoctylfluorene) as depicted in Figures 1c and 1d (except for TPA-Cz-sPF, where the green emission component might be attributed to exciplex or excimer emission, see the supporting information, SI).…”

Synthesis and assembly with mesoporous silica of platinum (II) porphyrin complexes bearing carbazyl groups: Luminescent and oxygen sensing properties

“…The emission wavelength (λ em ) and the photoluminescent quantum yields (Φ F ) of Pt-4Cn-TPP are presented in Table 1. At room temperature, Pt-4C4-TPP, Pt-4C6-TPP and Pt-4C8-TPP display higher photoluminescent quantum yields in solution than many other platinum (II) porphyrins [22] . …”