Photoluminescence and Quantum Yields of Urea and Urethane Cross-Linked Nanohybrids Derived from Carboxylic Acid Solvolysis Lianshe Fu, R. A. Sa ´ Ferreira, N. J. O. Silva, and L. D. Carlos* Departamento de Fı ´sica, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal V. de Zea Bermudez Departamento de Quı ´mica and CQ-VR, Universidade de Tra ´ s-os-Montes e Alto Douro, 5000-911 Vila Real Codex, Portugal J. Rocha Departamento de Quı ´mica, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal Received October 17, 2003. Revised Manuscript Received February 6, 2004 Urea and urethane cross-linked hybrids, classed as di-ureasils and di-urethanesils, were prepared through sol-gel derived carboxylic acid solvolysis. The resulting nanohybrids were characterized by X-ray diffraction, mid-infrared spectroscopy, 29 Si and 13 C nuclear magnetic resonance, and photoluminescence spectroscopy and results were compared with those of similar hybrid materials obtained from the conventional sol-gel route. The results indicate a similar structure for the hybrids, independent of the synthesis process used. All the hybrids are efficient room-temperature white-light emitters with emission quantum yields between 6 and 20%. The emission quantum yields of hybrids prepared through carboxylic acid solvolysis are 27-35% higher than those calculated for the di-ureasils and di-urethanesils synthesized via the conventional sol-gel technique. This is attributed to the presence of a larger number of nonbonded NH urea- and urethane-groups in the hybrids prepared by carboxylic acid solvolysis, illustrating the key role played by the synthetic method on the extent and magnitude of hydrogen bonding involving urea and urethane linkages. I. Introduction In the last two decades, the drive to miniaturization has been pushing industry into the atomic and nanom- eter scales requiring the development of new strategies for the synthesis of advanced materials. Among the available synthetic methods employed for the develop- ment of nanosystems, the sol-gel procedure presents advantages such as relatively low processing tempera- ture, high purity, improvement of the thermal and di- mensional stability of the resulting compounds, and ease of shaping the product into thin films, fibers, and monoliths. 1,2 Pure and well-controlled multifunctional organic-inorganic hybrids may be synthesized through a molecular nanotechnology “bottom-up” approach based on a tailored assembly of nanoscopic organic and inor- ganic building blocks. This opens up exciting new avenues in materials science and related technologies with significant implications in nanotechnological pro- cessing, which facilitate integration, miniaturization, and multifunctionalization of devices. 3-12 In particular, the sol-gel approach offers the flexibility necessary for implementing the chemical design strategies that are the basis of photonic hybrid materials, one of the most attractive fields for applications in the 21st century. 7,8,13-15 The outgrowth of new full color displays that are cheaper and less aggressive to the global environment is one of the main challenging tasks for the next gen- eration of flat-panel display systems and lighting tech- nology. The hybrid concept has been recently employed to synthesize stable and efficient full-color luminescent siloxane-based organic-inorganic materials lacking metal activator ions. 16-28 Emphasis is given to amide- or * Corresponding author. Phone: 351 234 370946. Fax: 351 234 424965. E-mail: lcarlos@fis.ua.pt. (1) Hench, L. L.; West, J. K. Chem. Rev. 1990, 90, 33. (2) Brinker, C. J.; Scherer, G. W. Sol-gel Science: The Physics and Chemistry of Sol-Gel Processing; Academic: San Diego, CA, 1990. (3) Novak, B. M. Adv. Mater. 1993, 5, 422. (4) Sanchez, C.; Ribot, F. New J. Chem. 1994, 18, 1007. (5) Schubert, U.; Hu ¨ sing, N.; Lorenz, A. Chem. Mater. 1995, 7, 2010. (6) Loy, D. A.; Shea, K. J. Chem. Rev. 1995, 95, 1431. (7) Judeinstein, P.; Sanchez, C. J. Mater. Chem. 1996, 6, 511. (8) Wen, J. Y.; Wilkes, G. L. Chem. Mater. 1996, 8, 1667. (9) Sanchez, C.; Ribot, F.; Lebeau, B. J. Mater. Chem. 1999, 9, 35. (10) Ahmad, Z.; Mark, J. E. Chem. Mater. 2001, 13, 3320. (11) Mitzi, D. B. Chem. Mater. 2001, 13, 3283. (12) Ben, F.; Boury, B.; Corriu, R. J. P. Adv. Mater. 2002, 14, 1081. (13) Schmidt, H.; Jonschker, G.; Goedicke, S.; Mennig, M. J. Sol- Gel Sci. Technol. 2000, 19, 39. (14) Sanchez, C.; Lebeau, B. In Hybrid Organic-Inorganic Materi- als; Loy, D. A., Ed.; Mater. Res. Soc. Bull. 2001, 26, 377. (15) Scott, B. J.; Wirnsberger, G.; Stucky, G. D. Chem. Mater. 2001, 13, 3140. (16) Green, W. H.; Le, K. P.; Grey, J.; Au, T. T.; Sail, M. J. Science 1997, 276, 1826. (17) (a) Bekiari, V.; Lianos, P. Langmuir 1998, 14, 3459. (b) Bekiari, V.; Lianos, P. Chem. Mater. 1998, 10, 3777. 1507 Chem. Mater. 2004, 16, 1507-1516 10.1021/cm035028z CCC: $27.50 © 2004 American Chemical Society Published on Web 03/19/2004