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Regiospecific Formation and Unusual Optical Properties of 2,5‐Bis(arylethynyl)rhodacyclopentadienes: A New Class of Luminescent Organometallics
Author(s) -
Steffen Andreas,
Ward Richard M.,
Tay Meng Guan,
Edkins Robert M.,
Seeler Fabian,
van Leeuwen Magda,
Pålsson LarsOlof,
Beeby Andrew,
Batsanov Andrei S.,
Howard Judith A. K.,
Marder Todd B.
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.201304068
Subject(s) - intersystem crossing , chemistry , ligand (biochemistry) , acceptor , luminescence , stereochemistry , crystallography , fluorescence , medicinal chemistry , photochemistry , excited state , materials science , singlet state , biochemistry , physics , receptor , quantum mechanics , nuclear physics , condensed matter physics , optoelectronics
A series of 2,5‐bis(arylethynyl)rhodacyclopentadienes has been prepared by a rare example of regiospecific reductive coupling of 1,4‐( p ‐R‐phenyl)‐1,3‐butadiynes (RH, Me, OMe, SMe, NMe 2 , CF 3 , CO 2 Me, CN, NO 2 , −CC‐( p ‐C 6 H 4 NHex 2 ), −CC( p ‐C 6 H 4 CO 2 Oct)) at [RhX(PMe 3 ) 4 ] ( 1 ) (X=−CCSiMe 3 ( a ), −CC‐( p ‐C 6 H 4 NMe 2 ) ( b ), −CCCC( p ‐C 6 H 4 NPh 2 ) ( c ) or CC{ p ‐C 6 H 4 ‐CC( p ‐C 6 H 4 ‐N(C 6 H 13 ) 2 )} ( d ) or Me ( e )), giving the 2,5‐bis(arylethynyl) isomer exclusively. The rhodacyclopentadienes bearing a methyl ligand in the equatorial plane (compound 1 e ) have been converted into their chloro analogues by reaction with HCl etherate. The rhodacycles thus obtained are stable to air and moisture in the solid state and the acceptor‐substituted compounds are even stable to air and moisture in solution. The photophysical properties of the rhodacyclopentadienes are highly unusual in that they exhibit, exclusively, fluorescence between 500–800 nm from the S 1 state, with quantum yields of Φ =0.01–0.18 and short lifetimes ( τ =0.45–8.20 ns). The triplet state formation ( Φ ISC =0.57 for 2 a ) is exceptionally slow, occurring on the nanosecond timescale. This is unexpected, because the Rh atom should normally facilitate intersystem crossing within femto‐ to picoseconds, leading to phosphorescence from the T 1 state. This work therefore highlights that in some transition‐metal complexes, the heavy atom can play a more subtle role in controlling the photophysical behavior than is commonly appreciated.