title: Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(ii) coordination platforms.
abstract: The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldiminato)Pt(ii) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone ligands. A series of non-vaulted and vaulted Pt complexes (1-5) with salicylaldehyde hydrazones as trans-coordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of the trans-bis(salicylaldiminato)Pt(ii) coordination platforms. X-ray diffraction and 2D NMR data demonstrated that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neighbouring N(2) lone pairs in the d-π conjugation of the trans-bis(salicylaldiminato)Pt(ii) platforms owing to conformational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-dimethyl analogues 2 made a much less significant contribution to the extension of the d-π conjugation, due to their high conformational mobility. Complexes 1-5 were found to have structure-dependent chromogenic properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes 1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and 5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(ii) complex 6. The introduction of MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic and bathochromic shifts, respectively. In addition, νmax- ET(30) plots for various solvents revealed that complexes 1-5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochromically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5. Complexes 1-5 also exhibit emission enhancement upon addition of excess CH3SO3H in dimethyl sulfoxide, and a significant effect of the linker on quantum yields (Φ77 K) was observed in the case of the vaulted complexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure dependence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone complexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d-π conjugation on the trans-bis(salicylaldiminato)Pt(ii) coordination platforms.
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Takumi
authors.initials: T
authors.lastname: Hashimoto
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Kanako
authors.initials: K
authors.lastname: Fukumoto
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Ngoc Ha-Thu
authors.initials: NH
authors.lastname: Le
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Matsuoka
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Kawamorita
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Naruyoshi
authors.initials: N
authors.lastname: Komiya
authors.affiliation: Department of Chemistry, Graduate School of Engineering Science, Osaka University, Machikaneyama, Toyonaka, Osaka 560-8531, Japan. naota@chem.es.osaka-u.ac.jp.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Naota