Synthesis and Photophysical Properties of Star-Shaped (D-π)3-A Molecules with an N-Heteroaromatic Core

Star-shaped pi-conjugated molecules, which are branched molecules with a general structure consisting of several (more than three) linear pi-conjugated chains connected to a central core, are an attractive target. This is because their molecular properties originating from the starshaped geometric and electronic structures can be different to their linear-shaped pi-conjugated analogues. Donor (D) -pi-acceptor (A) molecules, which are composed of donor (electron rich) and acceptor (electron deficient) segments connected by a pi-spacer, are also an attractive target due to their inherent photophysical properties based on the intramolecular charge transfer (ICT) process from a donor to an acceptor through a pi-spacer. Examples of such photophysical properties include a solvent-polarity responsive fluorescence from the highly-polarized ICT excited state (fluorosolvatochromism) and a cation responsive fluorescence of the D-pi-A molecule with an amino-donor-type cation receptor based on on -off switching of the ICT process triggered by a cation binding event. Our current efforts have focused on the synthesis and elucidation of the ICT-based photophysical functions of the star -shaped (D -703-A molecules which have a complexed structure of the star-shaped and D-pi -A structures. Herein, we report the synthesis and photophysical properties, including fluorosolvatochromic and proton -sensing properties of 2,4,6-tris(5-aryl-2-thienyl)-1,3,5-triazine, -pyrimidine, and -pyridine derivatives, which are designed as the star-shaped (D-pi)(3)-A molecules consisting of an electron deficient Nheteroaromatic core (A) and three donor aryl terminals (D) linked by a thiophene spacer (pi)