Silylated Coumarin Dyes in Sol−Gel Hosts. 2. Photostability and Sol−Gel Processing

Abstract

The photostability characteristics of numerous silylated coumarin dyes within SiO 2 xerogels and SiO 2 :PDMS Polyceram films, and of neat silylated coumarin dye films have been determined and related to the sol-gel processing conditions and host composition. FTIR spectroscopy was used to monitor the hydrolysis reaction rates of the silylated dyes and other Si-alkoxide precursors. The silylated dyes had varying reaction rates depending on the degree of functionality and the linkage between the alkoxide and the dye. Matching the reaction rates between TMOS and the silylated dye was accomplished by prehydrolysis of the silylated dye. The photostability of the dyes in the xerogels was measured by monitoring the drop in fluorescence intensity upon pumping with a N 2 laser and also by monitoring the drop in dye absorption upon irradiating the films with a UV lamp. At optimized prehydrolysis times, a silylated coumarin dye (derCoum) within a SiO 2 xerogel host demonstrated a 3-fold improvement in long-term photostability compared to its unsilylated counterpart. The use of a silylated dye results in covalently bonding the dye to the host matrix, increasing the probability that the dye will be caged and inhibiting dynamic processes which can lead to photodegradation. CP-MAS 29 Si NMR data for a derCoum xerogel confirmed that a large degree of dye bonding occurred. The addition of PDMS to the basic SiO 2 xerogel host composition had little effect on the photostability of the dye. The neat dye films showed improved fluorescence photostability with increase in hydrolysis time. These films showed poor photostability upon exposure to UV lamp degradation due to lower thermal degradation resistance and/or thermal conductivity compared to the SiO 2 xerogel films.

Porphyrinosilica and metalloporphyrinosilica: hybrid organic-inorganic materials prepared by sol-gel processing

“…Q peaks represents a quaternary oxygen tetrahedron and the superscripts denote the numbers of alkoxide or Si-OH groups that have reacted to form Si-O-Si linkages (Suratwala et al 1998). The chemical shifts of the Q peaks were identified by their relative positions and by assigned peak values from the literature (Engelhardt & Michel 1987).…”

Aniline incorporated silica nanobubbles

“…Incorporation of organic molecules such as dyes inside solid matrices is an attractive topic of research because of the photostability and fluorescence quantum yield [1][2][3] of the modified materials. An approach in this regard is to incorporate molecules inside silica spheres, 4,5 the advantage of this kind of nanoscopic containers is that they can be used to control the environment of the molecule.…”

Influence of pH and Dye Concentration on the Physical Properties and Microstructure of New Coumarin 4 Doped SiO2-PDMS ORMOSIL

“…elimination of translational freedom by avoiding inter-molecular interaction, immunization of optical properties from high concentration interferences, reduction in rotational relaxation of the excited state of laser dyes, elimination of inherent problems with physical pumping, ease of use and replacement, and fabrication of samples in the desired form and shape. 1 Amongst the several investigated organic dye doped ORMOSILs, [4][5][6][7][8][9][10][11][12] the chemical bonded SiO 2 -PDMS ORMOSIL is noted as a useful host-matrix for doping a dye. A detailed investigation on the SiO 2 -PDMS ORMOSIL has already been carried out in the present laboratory because the tetraethoxysilane (TEOS, an inorganic precursor for SiO 2 ) shows a controllable hydrolysis reaction rate and PDMS (poly(dimethylsiloxane)) possesses specific properties like transparency, hydrophobicity, good chemical and thermal stability and similarity of its backbone structure (-Si-O-) to that of TEOS.…”

“…15 Coumarin 4 was chosen as a organic dye because of its high fluorescence efficiency, chemical-and photo-stability. [7][8][9] It also exhibits specific molecular species associated with protonation-deprotanation reactions. [7][8][9] It was observed that the increase in the acid or base concentration increased the photo-luminescence peak intensity, which was attributed to an increase in the interaction between the gel matrix and the dye molecules.…”

“…[7][8][9] It also exhibits specific molecular species associated with protonation-deprotanation reactions. [7][8][9] It was observed that the increase in the acid or base concentration increased the photo-luminescence peak intensity, which was attributed to an increase in the interaction between the gel matrix and the dye molecules. 15 Concentration-quenching phenomenon was also noted with increasing dye concentration due to the deactivation process by the intermolecular energy transfer originating from the collision and aggregation of dye molecules.…”