Relaxation dynamics of 2,7- and 3,6-distyrylcarbazoles in solutions and in solid films: mechanism for efficient nonradiative deactivation in the 3,6-linked carbazole

We performed time-resolved spectral investigations of two distyrylcarbazole derivatives, 2,7- and 3,6-distyrylcarbazole (2,7-DPVTCz and 3,6-DPVTCz, respectively), in dilute toluene solution and in solid films mixed with poly(methyl methacrylate) (PMMA). The lifetime of 2,7-DPVTCz in its excited state in solution is approximately 100 times as great as that of 3,6-DPVTCz, consistent with their photophysical nature. The former shows intense emission, but the latter is nearly nonfluorescent in a free environment. Moreover, the lifetime of 3,6-DPVTCz in its excited state increased also approximately 100 times when the molecule was encapsulated in a 3,6-DPVTCz/PMMA solid film, indicating that intramolecular motion of the molecule significantly affects the observed relaxation dynamics in a confined environment. Calculations on the excited states indicate that an efficient intersystem crossing is activated upon twisting of the bridged C-C single bond in a free 3,6-linked carbazole; such efficient deactivation is impractical in 2,7-linked carbazole or for 3,6-linked carbazole in a PMMA matrix. Information obtained from experiments on femtosecond fluorescence enables us to distinguish crucial relaxation processes in the excited state for a profound understanding of the details of vibrational and electronic relaxations of 3,6-DPVTCz in solution.     

Two new compounds derived from bufalin

The biotransformation of bufalin by cell suspension cultures of Platycodon grandiflorus was investigated and two new biotransformed products were obtained,which was 3-epi-telocinobufagin and 3-epi-bufalin-3-O-β-D-glucoside.     

Stability analysis for uncertain nonlinear switched systems with infinite-time domain

Fuzzy Optimization and Decision Making - In this paper, an uncertain nonlinear switched system is a nonlinear switched system disturbed by subjective uncertainties, which can be illustrated by...     

Low energy asymptotics for Schrödinger operators with slowly decreasing potentials

Low energy behavior of Schrödinger operators with potentials which decay slowly at infinity is studied. It is shown that if the potential is positive then the zero energy is very regular and the resolvent is smooth near 0. This implies rapid local decay for the solutions of the Schrödinger equation. On the other hand, if the potential is negative then the resolvent has discontinuity at zero energy. Thus one cannot expect local decay faster than ordert ^–1 ast.     

Study of spontaneous combustion coals by GC and GC-MS

Organic geochemical characteristics of 3 Chinese spontaneous combustion coals have been carried out by means of GC and GC-MS analysis. It has been observed that more compounds with low to medium carbon number, such as terpenoids and others can be found in spontaneous combustion coals than in normal samples.     

2－（5－Br－2－吡啶偶氮－5－二乙氨基）－酚与铑的显色反应的研究及应用

本文研究了２－（－５－Ｂｒ－２吡啶偶氮－５－二乙氨基）－酚与铑（Ⅲ）的显色反应。在ｐＨ为４．０的邻苯二甲酸氢钾缓冲液介质中，Ｒｈ（Ⅲ）与试剂形成稳定的橙红色络合物，其组成比为１：４，最大吸收波长为４９０ｎｍ，表现摩尔吸光系数为１．３×１０￣５Ｌ·ｍｏｌ￣（－１）·ｃｍ￣（－１）。铑含量在０～４μｇ／１０ｍＬ范围内服从比尔定律。