Steady-State Spectroscopy to Single Out the Contact Ion Pair in Excited-State Proton Transfer.

Despite the outstanding relevance of proton transfer reactions, investigations of the solvent dependence on the elementary step are scarce. We present here a probe system of a pyrene-based photoacid and a phosphine oxide, which forms stable hydrogen-bonded complexes in aprotic solvents of a broad polarity range. By using a photoacid, an excited-state proton transfer (ESPT) along the hydrogen bond can be triggered by a photon and observed via fluorescence spectroscopy.

Toward Magic Photoacids: Proton Transfer in Concentrated Sulfuric Acid.

Photoacids are the most convenient way to deliver protons on demand. So far, their photoacidity allows for studying excited-state proton transfer (ESPT) only to protic or strongly basic solvent molecules. The strongest superphotoacids known so far exhibit excited-state lifetimes of their conjugate base on the order of 100 ps before recapturing the proton again.

(Oligo)aromatic species with one or two conjugated Si[double bond, length as m-dash]Si bonds: near-IR emission of anthracenyl-bridged tetrasiladiene.

A series of aryl disilenes TipSi[double bond, length as m-dash]Si(Tip)Ar (2a-c) and para-arylene bridged tetrasiladienes, TipSi[double bond, length as m-dash]Si(Tip)-LU-Si(Tip)[double bond, length as m-dash]SiTip (3a-d) are synthesized by the transfer of the TipSi[double bond, length as m-dash]SiTip unit to aryl halides and dihalides by nucleophilic disilenides TipSi[double bond, length as m-dash]SiTipLi (Tip = 2,4,6-iPrCH, Ar = aryl substituent, LU = para-arylene linking unit). The scope of the nucleophilic Si[double bond, length as m-dash]Si transfer reaction is demonstrated to also include substrates of considerable steric bulk such as mesityl or duryl halides Ar-X (Ar = Mes = 2,4,6-MeCH; Ar = Dur = 2,3,5,6-MeCH, X = Br or I). Bridged tetrasiladienes TipSi[double bond, length as m-dash]Si(Tip)-LU-Si(Tip)[double bond, length as m-dash]SiTip with more extended linking units surprisingly exhibit fluorescence at room temperature, albeit weak.