Self-Reversible Mechanochromism and Thermochromism of a Triphenylamine-Based Molecule: Tunable Fluorescence and Nanofabrication Studies

Abstract

A triphenylamine-based fluorophore, 4-((4-methoxyphenyl)(phenyl)amino)benzaldehyde (1), exhibits externalstimuli-responsive self-reversible solid-state fluorescence switching, tunable fluorescence, and a rare phenomenon of temperaturedependent fluorescence. Mechanically grinding a crystalline powder of 1 converts the blue fluorescence (λ max = 457 nm) to green (λ max = 502 nm), but blue fluorescence robustly self-recovers within 8 min. X-ray analysis and theoretical studies suggest that the change from a highly twisted molecular conformation and crystalline form into an amorphous phase with more planar conformation is responsible for the fluorescence switching. Self-reversible fluorescence switching did not show a significant change in fluorescence for several cycles of measurement. Interestingly, 1 in toluene showed a rare phenomenon of fluorescence enhancement with increasing temperature via activating more vibrational bands that lead to stronger twisted intramolecular charge-transfer (TICT) emissions. Morphological-change-mediated fluorescence tuning has also been demonstrated by fabricating nanoparticles of 1. The conversion of highly polydispersed, featureless, different-shaped nanoparticles into nearly uniformly sized spherical nanoparticles (20−25 nm) converts green (λ max = 502 nm) to blue fluorescence (λ max = 478 nm). The self-reversible multi-stimuli-responsive fluorescence switching and polymorphism and nanofabrication-mediated fluorescence tuning suggest its potential application in sensors, particularly for fluorescent thermometers.

Temperature-Controlled Locally Excited and Twisted Intramolecular Charge-Transfer State-Dependent Fluorescence Switching in Triphenylamine–Benzothiazole Derivatives

“…27,28 Although rarely reported, some of the TICT-active fluorophores showed enhancement of fluorescence with increasing temperature via activating more vibrational bands. 29−32 Alkyl-substituted organoboronium bisdiketone showed dramatic fluorescence thermochromism. 33 A ratiometric fluorescence thermometer with a positive temperature coefficient has been demonstrated using N , N -dimethyl-4-((2-methylquinolin-6-yl)ethynyl)aniline, a TICT-active molecule.…”

Highly emissive carbazole-based gold(i) complex with a long room-temperature phosphorescence lifetime and self-reversible mechanochromism characteristics

“…12 Meanwhile, it is also valuable for fundamental research and practical applications of mechanochromism materials to achieve spontaneous recovery of their mechanochromic luminescence without using any stimuli. 13 For example, self-reversible mechanochromism materials can be used to realize dynamic random access memory (DRAM). 14 In this article, we demonstrate a highly emissive carbazolebased gold(I) complex 1 with a long RTP lifetime (Scheme 1).…”

Contrasting Solid-State Fluorescence of Diynes with Small and Large Aryl Substituents: Crystal Packing Dependence and Stimuli-Responsive Fluorescence Switching

“…In addition, we report reversible fluorescence switching of some of the butadiynyl derivatives in the solid state by external heating and rubbing stimuli. Although there are reports on stimuli responsive fluorophores, [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] reports pertaining to a single fluorophore are still limited. Further, the potential of conjugated 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 diacetylenes as stimuli responsive fluorophores in the solid powder has not been looked at yet in the literature.…”