title: Preparation and acid-responsive photophysical properties of T-shaped π-conjugated molecules containing a benzimidazole junction.
abstract: T-shaped π-conjugated molecules with an N-methyl-benzimidazole junction have been synthesized and their acid-responsive photophysical properties owing to the change in the π-conjugation system are discussed. T-shaped π-conjugated molecules consist of two orthogonal π-conjugated systems including a phenyl thiophene extended from the 2-position and alkyl phenylenes connected through various π-spacers from the 4,7-positions of the N-methyl-benzimidazole junction. The π-spacers, such as thiophene, ethyne, and ethane, have an effect on the acid response of photophysical properties in terms of changes in conformation, excited-state energy and charge-transfer (CT) characteristics. In particular, the π-conjugated molecule with ethynyl spacers exhibited a marked redshift in the fluorescence spectrum with a large Stokes shift upon the addition of acid, whereas the other molecules showed substantial quenching. The redshift in emission was studied in detail by temperature-dependent fluorescence measurements, which indicated the transition to a CT state over the finite activation energy at the excited state. The change in the frontier molecular orbitals upon acid addition was further discussed by means of DFT calculations.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma, Nara 630-0192, Japan.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Inouchi
authors.forename: Takuya
authors.initials: T
authors.lastname: Nakashima
authors.forename: Masaya
authors.initials: M
authors.lastname: Toba
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kawai