RESUMO
Photochromic switches are essential for the control and manipulation of nanoscale reactions and processes. The expansion of their application to aqueous environments depends strongly on the development of optimized water-soluble photoswitches. Here we present a femtosecond time-resolved investigation of the photochromic reactions (transition between the open and the closed form) of a water-soluble indolylfulgimide. We observe a pronounced effect of the protic nature of water as a solvent on the ultrafast ring-opening reaction. Typically, the excited state of the closed form has a larger dipole moment than the ground state, which leads to stabilization of the excited state in polar solvents and hence a lifetime (3 ps) longer than in non-polar solvents (2 ps). However, in water, despite the increased solvent polarity and the increased excited state dipole moment, the opposite trend for the excited state lifetime is observed (1.8 ps). This effect is caused by the opening of a new excited state deactivation pathway involving proton transfer reactions.
RESUMO
Increasingly, educators are using the World-Wide Web (the Web) and related technology to supplement their traditional teaching materials. In this paper, we present a free tool that has been placed on the Web to enable educators to create Web pages that present self-scoring quizzes. Such Web-based practice quizzes provide students with an opportunity for interactive assessment and review of course material. The tool, Quiz-o-Matic, uses active server pages to build the HTML and JavaScript code for each quiz, without requiring the user to edit any code. We present evidence that students judge the self-scoring quizzes to be useful and worthwhile additions to a course.
