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Dynamic Properties of Molecular Tweezers with a Bis(2‐hydroxyphenyl)pyrimidine Backbone
Author(s) -
Tsuchido Yoshitaka,
Suzaki Yuji,
Ide Tomohito,
Osakada Kohtaro
Publication year - 2014
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.201304380
Subject(s) - chemistry , intramolecular force , hydrogen bond , molecular tweezers , molecule , substituent , pyrimidine , intermolecular force , ring (chemistry) , quantum yield , tweezers , stereochemistry , crystallography , photochemistry , fluorescence , supramolecular chemistry , organic chemistry , physics , quantum mechanics
4,6‐Bis(2‐hydroxyphenyl)‐2‐alkylpyrimidines with two anthryl or 9‐ethylnylanthryl substituents at the positions para to the OH groups prefer a U‐shaped conformation supported by two intramolecular OH ⋅⋅⋅ N hydrogen bonds in the solid state and in CDCl 3 solution. The compound with a hexyl substituent on the pyrimidine group and two 9‐ethynylanthryl arms at the hydroxyphenyl groups forms a 1:1 complex with 2,4,7‐trinitrofluorenone. Its association constant K a was estimated to be 2100 M −1 at 298 K, which is larger than those of other molecular tweezers ( K a <1000 M −1 ). DFT calculations suggested that the complex adopts a stable conformation supported by intramolecular hydrogen bonds among the OH groups and the pyrimidine ring as well as by intermolecular π–π interaction between the anthryl groups and 2,4,7‐trinitrofluorenone. Addition of n Bu 4 NF to a solution of the molecular tweezers or their complexes causes the cleavage of one or two OH ⋅⋅⋅ N hydrogen bonds, formation of new O ⋅⋅⋅ HF hydrogen bonds, and changes in the molecular conformation. The resulting structure of the molecular tweezers contains nonparallel anthryl groups, which do not bind the guest molecule. Photochemical measurements on 4,6‐bis(2‐hydroxyphenyl)‐2‐methylpyrimidine with two anthryl substituents showed negligible luminescence (quantum yield ϕ <0.01), owing to photoinduced electron transfer of the molecule with a U‐shaped structure. However, the O ‐hexylated compound exhibits emission from the anthryl groups with ϕ =0.39.