dried in a vacuum at 80 °C for 12 h. Dilute PVA solutions (5.0 g dm−3
in 70 v/v% ethanol/water) containing higher concentrations of 2 (2, 5,
10, and 30 w/w% with respect to PVA) were spin-coated for preparing
films with higher content of 2 (thickness: ∼0.1 μm).
Luminescence spectra of polymer films were recorded on a JASCO
FP-6600 spectrofluorophotometer equipped with an ILF-533 integral
sphere, and the quantum yields were calculated with a built-in software
based on a literature method.32 IR spectra were measured on a JEOL
WINSPEC100 spectrophotometer. Quantum chemical properties of
the enol and intramolecular proton-transferred (IPT) species of 1 and
2 were calculated by density functional theory (DFT) after geometry
optimization using B3LYP/6-311++G(d,p) basis set. The calculation
job files are presented in Supporting Information. These calculations
were performed with a Gaussian 09W, Gaussian Inc. (Revision
D.01).33