Electronic structure of tetra(4-aminophenyl)porphyrin studied by photoemission, UV–Vis spectroscopy and density functional theory

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao. b s t r a c tThe valence and conduction bands of a thin film of tetra(4-aminophenyl)porphyrin (TAPP) are investigated by direct and inverse photoemission as well as by comparison to density functional theory (DFT) calculations. By projecting the electronic eigenfunctions onto the molecular framework it was possible to interpret the origin of each spectroscopic feature. Although the majority of the photoemission spectrum is attributed to the unsubstituted tetraphenylporphyrin (TPP) parent molecule, several features are clearly due to the amino substitution. Substitution also has important consequences for the energy positions of the frontier orbitals and therefore on the low-energy electronic excitations. The measured electronic transport energy gap (E g = 1.85 eV) between the highest occupied molecular orbital (HOMO) and lowest unoccupied (LUMO) in TAPP is found to be significantly reduced with respect to TPP. Moreover, an increased energy separation between the two highest occupied states (HOMO and HOMO−1) is found both experimentally and by DFT calculations. Such evidence is attributed to an increased HOMO orbital destabilization due to an enhanced electron-donor character of the phenyl substituents upon amino functionalization. Finally, the above findings together with further time-dependent DFT calculations are used to interpret the effect of the amino groups on the UV-Vis absorption spectrum, namely an overall red-shift of the spectrum and remarkable intensity changes within the Q band.

Evaluation of Polyhedral Oligomeric Silsesquioxane Porphyrin Derivatives on Photodynamic Therapy

“…The specific emission wavelengths for the POSSPs are provided in Table 1. The S-and Q-bands of POSSPs 1-3 are slightly blue-shifted with respect to their parent porphyrin, ATPP or TAPP (Table S1 and Figure S1), most likely due to the change in the electron-donating effect of the nitrogen substituent in the para (4-phenyl) position when it is chemically transformed from an amine to an urea group, as has been reported in the literature [26]. On the contrary, the S-and Q-band for POSSPs 4 and 5 are slightly red-shifted in comparison to compound 6 (Table S1 and Figure S1).…”

Adsorption of Phosphonic-Acid-Functionalized Porphyrin Molecules on TiO2(110)

“…The highest occupied molecular orbital (HOMO) is located in the band gap at 2.1 eV below the Fermi level and corresponds to an electronic state with high electronic density at the macrocycle. 52 Notably, we also observe this state after adsorption of the same molecule replacing the phosphonic acid group with a carboxylic acid group. Finally, the Ti 3+ defect state of the substrate at 0.9 eV is attenuated, but still present after adsorption of the molecules.…”

Facile Synthesis of a Cubic Porphyrin-Based Covalent Organic Framework for Combined Breast Cancer Therapy

“…To find the reasons for the enhanced ROS generation ability, the band gaps of TFPP and CTP were measured (Figures S19 and S20). As shown in Figure g, TFPP exhibited a band gap of 1.74 eV, while CTP showed a narrowed band gap of 1.55 eV . The narrowed band gap should be attributed to the formation of the π-conjugation structure, which was conducive to the separation of e – and h + , thus enhancing the ROS generation ability. , As shown in Figure h, the US-generated e – in the conduction band of CTP could not reduce O 2 to O 2 –• but was negative enough to react with H 2 O 2 to produce • OH.…”

“… As shown in Figure g, TFPP exhibited a band gap of 1.74 eV, while CTP showed a narrowed band gap of 1.55 eV . The narrowed band gap should be attributed to the formation of the π-conjugation structure, which was conducive to the separation of e – and h + , thus enhancing the ROS generation ability. , As shown in Figure h, the US-generated e – in the conduction band of CTP could not reduce O 2 to O 2 –• but was negative enough to react with H 2 O 2 to produce • OH. Meanwhile, 1 O 2 could be directly formed from O 2 due to the higher potential of valence band holes. − Therefore, CTP could simultaneously produce 1 O 2 and • OH under US irradiation (Figure i).…”

“…The enhancement of the signal strength of CTP in the electron spin resonance spectrum further revealed the generation of 1 O 2 and the improvement of the 1 O 2 production efficiency (Figure c). Meanwhile, 3,3′,5,5′-tetramethylbenzidine was selected to detect the generation of • OH . For the CTP + H 2 O 2 + US group, there was a strong absorption peak at 654 nm.…”