Colorimetric photosensing of solvent polarity using photochromic spironaphthoxazine dye and its stimuli-responsive acrylic copolymer: A physico-chemical study

Abstract

Stimuli-responsive devices containing photoswitchable compounds have received a great deal of attention for constructing portable opto-chemical sensors in detection of solvent polarities. Here, photochromic and solvatochromic behavior of the synthesized spironaphtooxazine (SNO) and its acrylic copolymer (PCSN-3) in various protic and aprotic solvents were investigated experimentally and theoretically; and the results were exploited to fabricate a portable probe for colorimetric and spectroscopic detection of solvent polarity. The incorporation of SNO-based comonomer into the poly(methyl methacrylate) chains was approved by observing its functional groups in FTIR spectra and the efficiency of chemical incorporation was evaluated as 98.2% using 1HNMR analysis. DLS and SEM analyses demonstrated particles sizes of below 100 nm with spherical morphology and narrow size distributions. DFT calculation was used to predict plausible meronaphtooxazine (MNO) conformations and they were compared with the experimental results. UV–vis analyses showed that the maximum absorption intensity of MNO increased up to 20 folds in protic and aprotic solvents at −20 °C compared to those at room temperature. Hansen solubility parameter and solute-solvent interaction for SNO, MNO and PCSN-3 in different protic and aprotic solvents were measured by group contribution method for the first time. It was found that hydrogen bonding and solvent polarity are the determining parameters for solvatochromic behavior of SNO in protic solvents, while dispersibility parameter is dominant in aprotic solvents. Photochromism and solvatochromism of PCSN-3 film in aprotic solvents were studied similar to SNO. Interestingly, PCSN-3 film showed definite visual color change and spectroscopic feature for each solvent after UV irradiation at 365 nm, which establishes a promising solid-state portable probe for colorimetric photosensing of solvents polarity.