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Remarkable Solvatofluorochromism of a [2.2]Paracyclophane‐Containing Organoboron Complex: A Large Stokes Shift Promoted by Excited State Intramolecular Charge Transfer
Author(s) -
Tanaka Mirai,
Muraoka Shunsuke,
Matsui Yasunori,
Ohta Eisuke,
Sakai Atsushi,
Ogaki Takuya,
Yoshimoto Yuichi,
Mizuno Kazuhiko,
Ikeda Hiroshi
Publication year - 2017
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.201600028
Subject(s) - intramolecular force , excited state , stokes shift , chemistry , cyclohexane , photochemistry , electron acceptor , solvent , fluorescence , stereochemistry , atomic physics , organic chemistry , physics , quantum mechanics
An organoboron complex containing a [2.2]paracyclophanyl group ( 2 BF 2 ) exhibits remarkable solvatofluorochromism associated with a large Stokes shift. With increased solvent polarity, the fluorescence (FL) color of 2 BF 2 changes from sky blue ( λ FL =485 nm in cyclohexane ( c ‐C 6 H 12 )) to orange ( λ FL =576 nm in CH 3 CN). This behavior derives from the intramolecular charge transfer (ICT) character of the excited state 2 BF 2 * in which the [2.2]paracyclophanyl group serves as the electron donor while the remaining 2 BF 2 structure (apart from the sub‐benzene ring) functions as the electron acceptor. Wave deconvolution of FL spectra in a solvent mixture of CH 2 Cl 2 / c ‐C 6 H 12 , and a plot of the FL emission energy versus the CH 2 Cl 2 / c ‐C 6 H 12 ratio, suggest that FL of 2 BF 2 occurs from two types of 2 BF 2 * excited states. The results of DFT calculations support this explanation and further emphasize that the ICT character of 2 BF 2 * is derived from a large conformational change associated with the electron‐donating character of the [2.2]paracyclophanyl group. Moreover, the fact that 2 BF 2 is more sensitive than Reichardt's dye to polarity changes in a low polarity CH 2 Cl 2 / c ‐C 6 H 12 solvent mixture is also of importance.