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Thermally Activated Delayed Fluorescence in Fullerenes C ARLOS B ALEIZ ˜ AO AND ARIO N. B ERBERAN -S ANTOS Centro de Qu´ ımica-F´ ısica Molecular, Instituto Superior T´ecnico, Lisbon, Portugal This report reviews the thermally activated delayed fuorescence (TADF) displayed by ±ullerenes. From the analysis o± the steady-state data, time-resolved data, or by a combination o± both, it is possible to determine several important photophysical parameters o± ±ullerenes. Herein we also cover the development o± temperature and oxygen sensors based on the TADF e±±ect exhibited by ±ullerene C 70 . Despite the work already carried out, knowledge o± the photophysics o± ±ullerenes and derivatives is still incomplete, and much remains to be done in this area and in the improvement o± sensor systems based on ±ullerenes. Key words: ±ullerenes; C 60 ;C 70 ; thermally activated delayed fuorescence; temperature sensing; oxygen sensing Introduction The discovery of fullerenes in 1985 1 and their pro- duction in macroscopic amounts after 1990 2 opened a new Feld of research. Applications of fullerenes in areas, such as energy, materials, biopharmaceu- ticals, optics, and electronics, have started to ap- pear in recent years. The most common fullerenes are C 60 and C 70 , three-dimensional carbon struc- tures that can be viewed either as large car- bon molecules or as tiny nanoparticles with well- deFned composition and shape. Their photophys- ical and photochemical properties result from the many delocalized π electrons present and from the high symmetry and curvature of the structures. The photophysics of fullerenes has been the subject of considerable investigation. 3–5 One of the most char- acteristic and (to us) interesting photophysical prop- erties of C 60 ,C 70 , and derivatives, Frst observed in our group, is a second mechanism for ±uorescence, which is called thermally activated delayed ±uores- cence (TAD²). This phenomenon, which occurs in a few ±uorescent molecules, is usually weak; however, for fullerenes it is strong, especially for C 70 . Herein, we brie±y review the TAD² of fullerenes and the develop- ment of temperature and oxygen sensors based on this property. Address for correspondence: M´ario N. Berberan-Santos, Centro de Qu´ ımica-²´ ısica Molecular, Instituto Superior T´ecnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal. Voice: + 351-218419254; fax: + 351- 218464455. berberan@ist.utl.pt TADF: Fundamental Aspects Two distinct unimolecular mechanisms exist for molecular ±uorescence: prompt ±uorescence (P²) and TAD². 6 , 7 In the P² mechanism, emission occurs af- ter S n S 0 absorption and excited state relaxation to S 1 . The TAD² mechanism takes place by way of the triplet manifold: After excitation and once S 1 is attained, intersystem crossing (ISC) to the triplet man- ifold (T 1 or a higher triplet) occurs, followed by a sec- ond ISC from T 1 back to S 1 , and by ±uorescence emission proper. The cycle S 1 T 1 S 1 may be re- peated several times before ±uorescence Fnally takes place. TAD² is signiFcant only when the quantum
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.

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fulltext30 - Thermally Activated Delayed Fluorescence in...

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