Daylight-driven rechargeable antibacterial and antiviral nanofibrous membranes for bioprotective applications

Si, Yang; Zhang, Zheng; Wu, Wanrong; Fu, Qiuxia; Huang, Kang; Nitin, Nitin; Ding, Bin; Sun, Gang

To provide insight into the excitation features of the RNMs, we used time-dependent density functional theory (TD-DFT) calculations and diffuse reflection UV-visible (UV-vis) spectroscopy to evaluate the nature of the initial photoexcitation event. The TD-DFT calculations of the RNMs (see details in table S1) predict that the lower energy S 0 (ground state) → S 1 (lowest singlet excited state) excitations are negligible with very weak oscillator strength. Meanwhile, the S 0 → S n excitations of the RNMs are predicted to be dominant, and the calculated maximum wavelength (l max ) matched with the measured UV-vis spectra, as shown in Fig. 2 (A to D) . The l max of BA-RNM, BD-RNM, CA-RNM, and BDCA-RNM were 275, 307, 336, and 332 nm, respectively. Although these l max values were mainly located in the UV range, compared with the standard spectrum of D65 daylight, the light energy in the range from 300 to 450 nm can still be readily used by the RNMs, as shown in Fig. 2E . The estimated daylight absorbance coefficients (∫ 450 300 I l dl=∫I l dl) for BA-RNM, BD-RNM, CA-RNM, and BDCA-RNM were 21.62, 35.33, 66.04, and 45.41%, respectively, indicating a robust utilization of daylight source. After initial photon absorption, fast relaxation via internal conversion results in thermalization of the excited electron from S n to the S 1 , followed by ISC to the T 1 (lowest triplet excited state), where a series of photoreactions could originate (36, 37) . Inspection of the frontier orbitals of T 1 reveals qualitative differences in these RNMs. The BA-RNM and BD-RNM have similar n HOMO -p LUMO transitions in T 1 , with both n electron localized on carbonyl group and p electron localized over the entire conjugate system. In contrast, the CA-RNM exhibited a typical p HOMO -p LUMO transition with both p and p* orbitals localized on a phenyl ring system. Moreover, by the combination of the benzophenone and the polyphenol, the T 1 of BDCA-RNMs exhibits a unique charge transfer character with a n HOMO -p LUMO+3 transition (38) , where an electron occupying the HOMO orbital, which is an n orbital localized on the carbonyl group in benzophenone, is promoted into the spatially separated p*LUMO+3 localized on the conjugated system of CA.