*2.1. Chemicals and Materials*

All reagents were of analytical grade and used as received without further treatment. The FTO-coated glasses (<10 ohm sq<sup>−</sup>1) were purchased from Pilkington (Toledo, Ohio, USA). (3-Aminopropyl)trimethoxysilane (APS), polyetherimide (PEI), and propylene carbonate (PC) were purchased from the Aladdin Chemical Co., Ltd. and were used without further treatment. P2W17V was prepared according to a method reported in literature [26,27], and it was characterised by infrared (IR) spectroscopy (Figure S1), ultraviolet-visible (UV-vis) absorption spectroscopy (Figure S2), and cyclic voltammetry (CV) (Figure S3).
