trans–cis Photoisomerization of Azobenzene‐Conjugated Dithiolato‐Bipyridine Platinum(II) Complexes: Extension of Photoresponse to Longer Wavelengths and Photocontrollable Tristability

Abstract

Azobenzene derivatives modified with dithiolato-bipyridine platinum(II) complexes were synthesized, revealing their highly extended photoresponses to the long wavelength region as well as unique photocontrollable tristability. The absorptions of trans-1 and trans-2 with one azobenzene group on the dithiolene and bipyridine ligands, respectively, cover the range from 300 to 700 nm. These absorptions are ascribed, by means of time-dependent (TD)DFT calculations, to transitions from dithiolene(pi) to bipyridine(pi*), namely, interligand charge transfer (CT), pi-pi*, and n-pi* transitions of the azobenzene unit, and pi-pi* transitions of the bipyridine ligand. In addition, only trans-1 shows distinctive electronic bands, assignable to transitions from the dithiolene(pi) to azobenzene(pi*), defined as intraligand CT. Complex 1 shows photoisomerization behavior opposite to that of azobenzene: trans-to-cis and cis-to-trans conversions proceed with 405 and 312 nm irradiation, which correspond to excitation with the intraligand CT, and pi-pi* bands of the azobenzene and bipyridine units, respectively. In contrast, complex 2 shows photoisomerization similar to that of azobenzene: trans-to-cis and cis-to-trans transformations occur with 365 and 405 nm irradiation, respectively. Irradiation at 578 nm, corresponding to excitation of the interligand CT transitions, results in cis-to-trans conversion of both 1 and 2, which is the longest wavelength ever reported to effect the photoisomerization of the azobenzene group. The absorption and photochromism of 4, which has azobenzene groups on both the dithiolato and bipyridine ligands, have characteristics quite similar to those of 1 and 2, which furnishes 4 with photocontrollable tristability in a single molecule using light at 365, 405, and 578 nm. We also clarified that 1 and 2 have high photoisomerization efficiencies, and good thermal stability of the cis forms. Complexes 3 and 5 have almost the identical photoresponse to those of their positional isomers, complexes 2 and 4.

Azobenzene-functionalized iridium(iii) triscyclometalated complexes

“…There is a considerable amount of examples of azobenzenecontaining coordination compounds, mainly based on neutral nitrogen or phosphorus based ligands: phosphine, [10][11][12][13] pyridine, 5,14 2,2′-bipyridine, [15][16][17][18][19][20][21][22][23][24] terpyridine, 6,[24][25][26][27] or bridging azobis(4-pyridine) [28][29][30][31][32][33][34] ligands. Despite the fact that organometallic complexes (containing a C-metal bond) are used in a wide number of important applications-setting aside ferrocene derivatives 5,[35][36][37] -only a handful of examples of azobenzene based organometallics are known.…”

Synthesis, Spectral Characteristics and DFT Studies of the New Dye 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) in Different Solvents

“…4). With the change in the excitation wavelength from 365 to 450 nm, the position of the emission remains unchanged, which suggests that this band is a true emission band and not due to any second order diffraction of the excitation light [22][23][24] (Fig. 5).…”

Induction of E/Z isomerization in a pendant metal-bound azobenzene: a synthetic, spectroscopic and theoretical study

“…[1][2][3][4] Azobenzene has been appended to a number of chromophores, including transition metal complexes, in an attempt to couple the E/Z isomerization process to an external electronic transition. [5][6][7][8][9][10][11][12][13] Transition metal compounds that exhibit metal to ligand charge transfer transitions (MLCT), as seen in many d 6 metal complexes, are ideal for transferring energy to an external group. [14][15][16][17][18] In this report, we present a study of two Re(CO) 3 diimine complexes with a pendant azobenzene group.…”