A soluble cryogenic thermometer with high sensitivity based on excited-state configuration transformations

Abstract

Cryogenic temperature detection plays an irreplaceable role in exploring nature. Developing high sensitivity, accurate, observable and convenient measurements of cryogenic temperature is not only a challenge but also an opportunity for the thermometer field. The small molecule 9-(9,9-dimethyl-9H-fluoren-3yl)-14-phenyl-9,14-dihydrodibenzo[a,c]phenazine (FIPAC) in 2-methyl-tetrahydrofuran (MeTHF) solution is utilized for the detection of cryogenic temperature with a wide range from 138 K to 343 K. This system possesses significantly high sensitivity at low temperature, which reaches as high as 19.4% K(-1) at 138 K. The temperature-dependent ratio of the dual emission intensity can be fitted as a single-exponential curve as a function of temperature. This single-exponential curve can be explained by the mechanism that the dual emission feature of FIPAC results from the excited-state configuration transformations upon heating or cooling, which is very different from the previously reported mechanisms. Here, our work gives an overall interpretation for this mechanism. Therefore, application of FIPAC as a cryogenic thermometer is experimentally and theoretically feasible.

Dual‐Emitting Dihydrophenazines for Highly Sensitive and Ratiometric Thermometry over a Wide Temperature Range

“…Among the numerous temperature‐determining schemes developed so far, more and more research interest has been captured by the luminescence‐based sensing methods, due to their noninvasiveness, fast response, high spatial resolution, capability of real‐time/on‐line and in‐situ monitoring, capacity to resist strong electro/magnetic fields, and ability to work with high‐speed moving objects . A large variety of luminescent thermometers including metal salts, oxides and complexes, metal–organic frameworks, nanoclusters/nanocrystals, quantum dots (QDs), organometallics, organic dyes, and polymers, have already been developed. However, a large portion of the existing luminescent thermometry protocols are dependent on the emission intensity decreasing with the temperature increase as a result of the thermal activation of the nonradiative decay pathways.…”

“…It is because that ratiometric probing mode can eliminate the intensity fluctuations exerted by the quantity of luminophore, excitation power, detection efficiency, and the sample morphology, displaying a self‐calibrating readout. [6–11b,13,18,19] It is therefore highly demanded to devise ratiometric temperature‐sensing schemes.…”

“…N , N ′‐disubstituted‐dihydrophenazine derivatives are a class of recently explored fantastic luminophores which show dual FL and intriguing phenomenon of vibration‐induced emission (VIE). [19a,22,23] Such luminogens have drawn increasing attention for its great potential in ratiometric probing. [19a,22b,d,e] At room temperature, when the molecules of N , N ′‐disubstituted‐dihydrophenazines are rigidified, intrinsic blue FL dominates their FL spectra, while when their molecules are unconstrained, the orange‐red FL takes the dominating place.…”

“…[19a,22,23] Such luminogens have drawn increasing attention for its great potential in ratiometric probing. [19a,22b,d,e] At room temperature, when the molecules of N , N ′‐disubstituted‐dihydrophenazines are rigidified, intrinsic blue FL dominates their FL spectra, while when their molecules are unconstrained, the orange‐red FL takes the dominating place. The blue FL is ascribed to the intrinsic emission of these N , N ′‐disubstituted‐dihydrophenazines, for the saddle‐shaped configurations limit the overall conjugation length, whereas the orange‐red FL band originates from the planar conformation derived by the bent‐to‐planar vibration which elongates the π‐conjugation.…”

Ratiometric Hg2+/Ag+ Probes with Orange Red‐White‐Blue Fluorescence Response Constructed by Integrating Vibration‐Induced Emission with an Aggregation‐Induced Emission Motif

“…In the aggregated or solid state, the fluorescence is dominated by the blue emission as a result of the restriction of intramolecular vibrations of the central dihydrodibenzo[ a , c ]phenazine moiety. So far, the VIE effect has been systematically studied and interpreted in detail by our group . Owing to the unique dual‐emission feature, VIE‐active fluorogens, such as dihydrophenazine derivatives, usually exhibit multicolor and wide‐spectrum responses to environmental changes and hence are suitable for development as ratiometric probes.…”