Reversible vapochromic response of polymer films doped with a highly emissive molecular rotor

Abstract

We report on a new vapochromic system suitable for sensing volatile organic compounds (VOCs) based on polymer films doped with 4-(diphenylamino)phthalonitrile (DPAP), a fluorescent molecular rotor sensitive to both solvent polarity and viscosity. Poly(methyl methacrylate) (PMMA) and polycarbonate (PC) films containing small amounts of DPAP (#0.1 wt%) were prepared and exposed to saturated atmospheres of different VOCs. DPAP/PMMA films show a good and reversible vapochromism when exposed to VOCs with high polarity index and favourable interaction with polymer matrices such as THF, CHCl 3 , and acetonitrile. Analogously, DPAP/PC films exposed to polar and highly polymer-interacting solvents, that is, toluene, THF, and CHCl 3 , show a gradual decrease and red-shift of the emission. In contrast to DPAP/ PMMA films, an unexpected increase and further red-shift of fluorescence are observed at longer exposure times as a consequence of an irreversible, solvent-induced crystallization process of PC. The vapochromism of DPAP-doped films is rationalized on the basis of alterations of the rotor intramolecular motion and polarity effects stemming from the environment, which, in concert, influence the deactivation pathways of the DPAP intramolecular charge transfer state. Overall, the present results support the use of DPAP-enriched plastic films as a new chromogenic material suitable for the detection of VOCs.

“N-alkyl diketopyrrolopyrrole-based fluorophores for luminescent solar concentrators: Effect of the alkyl chain on dye efficiency”

“…Film thickness = 15 ± 5 µm; λ exc = 525 nmThe absorption spectra of 1c/PMMA and 2c/PMMA films show large absorption bands with two maxima positioned at 513-550 nm and at 570-607 nm, respectively. These values are equivalent to those collected in CHCl 3 solution due to the similar polarity indexes of the dispersing media [50].…”

A fluorescent molecular rotor showing vapochromism, aggregation-induced emission, and environmental sensing in living cells

“…In all cases, solvent vapors could be reversibly adsorbed by and removed from the films, with no apparent loss of emission efficiency. These results support the use of TPAP and structurally-related compounds 22 as new chromogenic materials suitable for the detection of volatile organic compounds (VOCs). Notably, the recent application of the hue parameter of the HSV color-space for spectral fluorescent sensing 23 could open up the way to a cost-effective way to identify vapours and vapour mixtures by means of inexpensive RGB cameras.…”

Vapochromic polyketone films based on aggregation‐induced enhanced emission

“…In addition, pressing issues in global security are triggering the design of novel chromogenic compounds aimed at detecting environment changes with optical responses even more effective. For example, thermoplastic indicators containing fluorophore sensitive to viscosity changes have been used with success for the detection of VOCs . Notably, plastic films containing moderate amounts of the chromophoric probe (<0.1 wt%) display fluorescence variations upon the exposure to well‐interacting VOCs due to an induced plasticization of the continuous polymer phase .…”

“…For example, thermoplastic indicators containing fluorophore sensitive to viscosity changes have been used with success for the detection of VOCs . Notably, plastic films containing moderate amounts of the chromophoric probe (<0.1 wt%) display fluorescence variations upon the exposure to well‐interacting VOCs due to an induced plasticization of the continuous polymer phase . Plasticization means also viscosity decreasing, thus allowing the dispersed fluorophores to aggregate together upon a certain concentration threshold, which in turn causes evident color changes.…”

“…[3][4][5][6][7][8][9][10][11][12] Notably, plastic films containing moderate amounts of the chromophoric probe (<0.1 wt%) display fluorescence variations upon the exposure to well-interacting VOCs due to an induced plasticization of the continuous polymer phase. [3][4][5][6]9,13 Plasticization means also viscosity decreasing, thus allowing the dispersed fluorophores to aggregate together upon a certain concentration threshold, which in turn causes evident color changes. In this context, the 4,4′-bis(2benzoxazolyl)stilbene (BBS) dye has been demonstrated to be an effective probe for the determination of polymer mechanical solicitations and thermal stress.…”