Carbonium ions with multiple neighboring groups. II. Physical studies

Artificial Molecular Rotors

“…With NMR, chemists had a readily accessible and relatively straightforward method to observe concerted rotations in “cogwheel-like” systems, and in the four decades following 1965, the number of papers increased dramatically. Breslow and co-workers revisited the triarylcarbonium ions for geared rotations using DNMR, as did Rakshys et al , Other groups investigated similar behavior in diaryl ethers ( 8 ), , diaryl sulfides ( 9 ), , diphenyl ketones ( 10 ), and polyarylmethane derivatives (section 5.1.3), − to name a few. In the 1970s, 1980s, and 1990s and up to the present, many groups have returned to the concept of correlated rotation in a number of systems.…”

“…Many reviews have appeared, ,,,− ,− ,,− and the reader is directed to them for a more detailed discussion. Polyarene propellers can generally be classified into two subsets: (a) those arranged around a central atom (Figure ), as in diarylsulfoxides, diaryl sulfones, diaryl sulfides, diaryl ketones, and diaryl ethers ( 29 ; X = SO, SO 2 , S, CO, respectively), − ,− di- and triarylboranes ( 30 ; Z = B), − diarylmethanes and derivatives ( 29 ; X = CH 2 ), − ,,,− triarylmethanes ( 30 ; Z = CH) and trityl cations ( 30 ; Z = C + ), − ,− ,,,− ,− tetraarylmethanes ( 31 ), triarylamines ( 30 ; Z = N), , triarylphosphines ( 30 ; Z = P) and derivatives, − and polyarylated ethanes, ethenes ( 32 ; R = R‘ = H), ethenols ( 32 ; R = H, R‘ = OH), and ethenones, ,−…”

“…Polyarene propellers can generally be classified into two subsets: (a) those arranged around a central atom (Figure 18), as in diarylsulfoxides, diaryl sulfones, diaryl sulfides, diaryl ketones, and diaryl ethers (29; X ) SO, SO 2 , S, CO, respectively), [235][236][237][323][324][325][326][327][328][329][330] di-and triarylboranes (30; Z ) B), [331][332][333] diarylmethanes and derivatives (29; X ) CH 2 ), [227][228][229]238,241,[334][335][336][337][338][339][340] triarylmethanes (30; Z ) CH) and trityl cations (30; Z ) C + ), [220][221][222][223][224][225][231][232][233]239,240,[331][332][333][341][342][343][344][345]…”

Recent applications of bifunctional trityl groups

“…30 Interestingly, a 'sulfuric analogue' of a DMTr + cation, where both oxygens are replaced by sulfur, is somewhat less stabilized, but thioethers exert a much stronger bathochromic effect on the UV/Vis spectrum. 31 Coloured cations from various trityls were used for encoding in oligonucleotide synthesis. 32 Each triarylmethyl group was used for 5A-O protection of a particular nucleoside in solid phase procedure.…”

“…However this correlates well with the earlier data on triphenylmethinium ions. 31 The attractive combination of second-order optical nonlinearities (of octupolar origin) in combination with almost complete transparency in the useful (visible) frequency range for triarylmethyl cations, and interesting electrochemical properties of star-shaped conducting polymers (based on oligothienyls) which could be useful for a wide range of potential applications led to the development of oligothienylic trityls 63. 40b,c High off-resonant second-order non-linear coefficients have been reported, although further optimization of the donor and acceptor groups is needed.…”