Premium
Amide‐Based Molecular Knots as Platforms for Fluorescent Switches
Author(s) -
Passaniti Paolo,
Ceroni Paola,
Balzani Vincenzo,
Lukin Oleg,
Yoneva Albena,
Vögtle Fritz
Publication year - 2006
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.200600350
Subject(s) - protonation , fluorescence , chemistry , excited state , photochemistry , amide , absorption (acoustics) , emission spectrum , spectral line , organic chemistry , materials science , ion , physics , quantum mechanics , astronomy , nuclear physics , composite material
Abstract A series of amide‐based molecular knots equipped selectively with fluorescent dansyl and/or pyrenesulfonyl moieties were synthesized from the readily available tris(allyloxy)knotane. UV/Vis absorption spectra, emission spectra, and the emission lifetimes of the fluorescent knotanes were investigated in chloroform at 298 K. The absorption spectra of the knotanes correspond to those of mixtures of their UV‐active constituents. The fluorescence quantum yields and lifetimes of the dansyl and pyrenesulfonyl moieties are partly quenched by the knotane platform. In the KN ( Da ) 2 ( Py ) species, the fluorescent excited state of the dansyl units ( λ max =510 nm) lies at lower energy than the fluorescent excited state of the pyrenesulfonyl unit ( λ max =385 nm), the emission of which is accordingly quenched with sensitization of the dansyl fluorescence. In the KN ( Ao ) 2 ( Da ), KN ( Ao )( Da ) 2 , and KN ( Da ) 3 species, the addition of acids causes the protonation of their dansyl units with a consequent decrease in the intensity of the dansyl band at 510 nm and appearance of the emission band of the protonated dansyl unit ( λ max =340 nm). Each dansyl unit of KN ( Ao )( Da ) 2 and KN ( Da ) 3 undergoes the independent protonation. In these incompletely protonated knotanes the fluorescence of the protonated dansyl units is partly quenched by nonprotonated ones. These processes can be quantitatively reversed upon addition of a base. In KN ( Da ) 2 ( Py ), an increase of the fluorescence of its pyrenesulfonyl group is observed when the dansyl groups are protonated. The results obtained show that the readily available and easily functionalizable amide‐knotanes can be used as an interesting scaffold to obtain fluorescent switches.