Fig. 3 | Nature Communications

Fig. 3

From: Solvatochromic covalent organic frameworks

Fig. 3

Solvatochromism of Py–TT COF oriented thin films. a GIWAXS pattern of a 360 nm thick Py–TT COF film grown on a sapphire substrate. The intensity of hk0 reflections is concentrated directly above the sample horizon, whereas the 001 and other low-index hk1 reflections appear close to the substrate normal. b UV–Vis absorption spectra of the Py–TT COF film recorded at different relative pressures of H2O in N2. Increasing water content causes a strong absorption increase in the 520–640 nm region, accompanied by a reduced absorption in the 440–500 nm and 280–380 nm regions. Insets, photographs of the COF film in the dry and water-saturated states. c Corresponding plot of the humidity-induced absorbance changes, AhumidAdry, at different H2O relative pressures. The grey line indicates the wavelength used for the response time measurements (see below). d UV–Vis spectra of the same COF film in saturated atmospheres of various solvents. The solvatochromic shift increases monotonically with increasing ETN polarity of the solvents. e Solvatochromic response of the Py–TT COF film towards step changes between dry and H2O-saturated N2 streams. Ten individual data sets (black dots) recorded at λ = 560 nm have been averaged (red line). The response times τrise and τfall are determined between the 10% and 90% thresholds. f TD-DFT calculated electron density difference upon the one-electron excitation from the ground state (S0) to the first singlet excited state (S1). This transition involves a reduction of the electron density on the pyrene moieties and an electron density gain of the thienothiophene bridges, and hence possesses a pronounced charge-transfer character. Electron density isosurfaces are displayed at an isovalue of 5e−5

Back to article page