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Tetraazaperopyrenes: A New Class of Multifunctional Chromophores
Author(s) -
Riehm Till,
De Paoli Gabriele,
Konradsson Asgeir E.,
De Cola Luisa,
Wadepohl Hubert,
Gade Lutz H.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200700383
Subject(s) - bathochromic shift , chemistry , protonation , proton affinity , chromophore , molecule , absorption (acoustics) , absorption band , solvent , absorption spectroscopy , photochemistry , crystallography , organic chemistry , materials science , ion , fluorescence , physics , quantum mechanics , optics , composite material
Tetraazaperopyrene and a range of derivatives have been synthesised and their photophysical and redox‐chemical properties studied. The parent compound, 1,3,8,10‐tetraazaperopyrene ( 1 ), was prepared by treating 4,9‐diamino‐3,10‐perylenequinone diimine with triethyl orthoformate, whereas the 2,9‐disubstituted derivatives of 1 were obtained after treatment with the corresponding carboxylic acid chloride or anhydride (2 mol equiv). The 1,3,8,10‐tetraazaperopyrene core structure was established by X‐ray diffraction of 2,9‐bis(2‐bromophenyl)‐1,3,8,10‐tetraazaperopyrene ( 6 ). The UV‐visible absorption spectra of the compounds have a characteristic visible π * ←π absorption band at 440 nm (log ε max =4.80) with a strong vibrational progression (Δ ν ≈1450 cm −1 ). Diprotonation of the nitrogen atoms induces a bathochromic shift of this band from 430–440 to 470–480 nm and all four nitrogen atoms are protonated when pure H 2 SO 4 is used as the solvent. The first and second as well as the third and fourth protonations occur concomitantly, which implies that they have very similar p K a values and, consequently, similar proton affinities. A theoretical study of the proton affinities in the gas phase and in solution attributes this behaviour to the effects of polar solvents, which dampen the charge of a protonated site at the other end of the molecule and thus effectively decouple the two opposite pyrimidine units in the polycondensed aromatic compound. The photophysical data were modelled in a time‐dependent DFT study of 1 , 1 H 2 2+ and 1 H 4 4+ in both the gas phase and in a polar solvent. All the dyes show weak fluorescence in organic solvents, however, their protonated conjugate acids show dramatically increased fluorescence intensity. All of the dyes undergo two electrochemically reversible one‐electron reductions with cyclovoltammetric half‐wave potentials at E red1 ≈−0.9 V and E red2 ≈−1.3 V (vs. SCE), which are associated with characteristic spectral changes.