Luminescent Molecular Thermometers

Abstract

Temperature is one of the most important factors that affects our daily lives. Everyone can recognize the arrival of spring by feeling the warmth in the air. Every chef pays attention to the temperature of a frying pan and an oven. In science, all phenomena, for example, chemical reactions or color of a star, are influenced by temperature. Therefore methods for measuring temperature remain in vogue. Until now, various types of thermometers have been developed, such as liquid-filled bulbs and stems (alcohol and mercury thermometers), bimetal strips, metallic resistors, thermistors, thermoelectric devices (thermocouples), and infrared radiation detectors (thermography) (1).A molecule that responds to heat and sends the information about temperature in the form of a light signal (e.g., fluorescence) is called a luminescent molecular thermometer (LMT). Such a "smart" molecule is able to function as a molecular-level thermometer (2, 3) in the scientific world. LMTs have a great advantage over other thermometers in measuring temperatures in a small space (with dimensions of < 10 ᎑3 m), since the fluorescence detection is highly sensitive and enables us to observe even one molecule (with a size of ∼10 ᎑9 m) (4). To measure two-or three-dimensional temperature distribution in space and to obtain the time sequence of temperature in a dewdrop, a living cell, a microfluidic channel, or a microreactor are a few of the goals in the application of LMTs. All of these places are too small for macroscopic thermometers but large enough to accommodate the smart molecular reporter.Thermally-driven Boltzmann-type distribution between two competing or equilibrating states is a useful model to rationalize most observations with luminescent molecular thermometers. If the two states show a difference in fluorescence quantum yield (Φ f ) (or fluorescence intensity), fluorescence lifetime (τ f ), or maximum emission wavelength (λ em ), the molecule can be used as a LMT. In this article, LMTs are classified into nine categories based on the spatial relationship between two competing or equilibrating states as shown in Table

Thermally Activated Delayed Fluorescence in Fullerenes

“…Real‐time temperature monitoring is of paramount importance in industrial testing and manufacturing and in many biomedical diagnostic and treatment processes. There are several thermal sensors based on molecular optical properties, namely, luminescence 36 . The use of fiber optics in conjugation with phosphors, whose luminescence lifetime changes with temperature, is a well‐established method 37 .…”

Near infrared absorbing near infrared emitting highly-sensitive luminescent nanothermometer based on Nd3+ to Yb3+ energy transfer

“…Since many tools (e.g. Therefore, much effort has been devoted to develop luminescent thermometers displaying satisfactory sensitivity and high photostability, which are suitable for sensing the temperature at large depths and in heterogenous tissues [5][6][7][8][9] . may be compacted into single theranostic nanoparticle, the range of possibilities seems enormous.…”

Thermometry at the nanoscale

“…It works remotely with high detection sensitivity and spatial resolution in short acquisition times, even in biological fluids, strong electromagnetic fields and fast-moving objects. 19,61,[69][70][71][72][73] The thermal probes encompass organic dyes, ruthenium complexes, spin crossover NPs, polymers, LDHs, semiconductor QDs, and Ln 3+ -based materials. Apart from these simple systems, in which a single component acts as a temperature-responsive emitting centre, there are complex systems, in which the changes in the emission intensity and/or lifetime of the emitting state of a particular component are induced by a second one that is the real temperature responsive material.…”