Photoisomerization of Pt^II Complexes Containing Two Different Photochromic Chromophores: Boron Chromophore versus Dithienylethene Chromophore

Abstract

In order to examine competitive photoisomerization, a series of novel photochromic PtII molecules that contain both dithienylethene (DTE) and B(ppy)Mes2 units (ppy=2‐phenylpyridine, Mes=mesityl) were successfully synthesized and fully structurally characterized. Their photochromic properties were examined by UV/Vis, emission and NMR spectroscopy. It was found that the DTE unit in all three compounds is the preferred photoisomerization site, exhibiting reversible photochromism with irradiation. The B(ppy)Mes2 unit does not undergo photoisomerization in these molecules, but likely enhances the photoisomerization quantum efficiency of the DTE moiety through the antenna effect. Extended irradiation with UV light leads to the rearrangement of the ring‐closed isomers of DTE. TD‐DFT computational studies indicate that the DTE photocyclization proceeds via a triplet pathway through an efficient energy transfer process.

Recent advances in the synthesis of luminescent tetra-coordinated boron compounds

“…Variable temperature emission experiments reveal that the regioisomer with the internal B-N bond showed temperature dependent structural dynamics which was supported by TD-DFT calculations. They 89 The same group also 90 synthesized and characterized Pt(II) complexes that contain dithienylethene (DTE) and B( ppy)Mes 2 as photochromic units (58)(59)(60). UV/Vis and NMR experiments showed that only DTE units of all the complexes undergo reversible photoisomerization under UV light irradiation.…”

Recent Advances in π-Conjugated N^C-Chelate Organoboron Materials

“…Similarly, cyclometallation of the N^C ligands also quenched the photoisomerization process of the B(ppy)Mes2 chromophore [40]. Several other studies have been carried out to obtain an in-depth knowledge of such chromophores and more can be found in references [38,[41][42][43][44][45][46]. Through various structural modifications and analogues, it has been established that photoisomerization could also be extended to N^C-chelate in addition to the ppy systems [47].…”

“…Similarly, cyclometallation of the NˆC ligands also quenched the photoisomerization process of the B(ppy)Mes 2 chromophore [40]. Several other studies have been carried out to obtain an in-depth knowledge of such chromophores and more can be found in references [38,[41][42][43][44][45][46]. In order to examine the competitive photoisomerization processes, Wang and coworkers [38] prepared a series of cis and trans Pt(II) acetylides containing two photochromic units; i.e., dithienylethene (DTE) and B(ppy)Mes2 (7a-c, Figure 5).…”

“…Several other studies have been carried out to obtain an in-depth knowledge of such chromophores and more can be found in references [38,[41][42][43][44][45][46]. In order to examine the competitive photoisomerization processes, Wang and coworkers [38] prepared a series of cis and trans Pt(II) acetylides containing two photochromic units; i.e., dithienylethene (DTE) and B(ppy)Mes2 (7a-c, Figure 5). Interestingly, in such systems, DTE showed preferential reversible photochromism over the boryl unit while the latter enhanced photoisomerization quantum efficiency of the DTE via antenna effect.…”

Two cyclometalated Pt(ii) complexes showing reversible phosphorescence switching due to grinding-induced destruction and crystallization-induced formation of supramolecular dimer structure

“…It is well known that dithienylethene (DTE) is a class of fascinating organic compounds, showing photochromism due to light-irradiation-induced structural transition between open form and closed form (Scheme S1 †). 16 So far, some DTE-based Pt(II) complexes have been reported, in which various DTE ligands coordinate with Pt(II) ions through some functional groups such as alkynyl group, [17][18][19][20][21] pyridyl group, 22 1,10-phenanthroline unit, 23 2-(thiophen-2-yl)-pyridine moiety, 24 2-(2-pyridyl)imidazole moiety, 25 and 1,3-di(2-pyridyl)benzene unit. 26 Some complexes were found to exhibit phtochromism, and even signicant switching of either luminescence or nonlinear optical (NLO) property due to the open/closed isomerization of DTE unit.…”