To design novel dyes with a controllable fluorescence on-off switching mechanism, understanding the dark state at the atomic level should be a key focus. In this study, we focused on the radiative and nonradiative mechanisms of 4′-N,N-diethylamino-3-hydroxyflavone (DEAHF) based on theoretical and experimental viewpoints. In the excited state, an excited-state intramolecular proton transfer (ESIPT) reaction of DEAHF occurs, and both the normal (N*) and tautomer (T*) forms exist in solution. To discuss the electronic structure changes through ESIPT, we mainly focused on two structural changes: the rotation of the diethylamino group and the bending motion of DEAHF in the excited state. The potential energy surfaces (PESs) passing through the rotation of the diethylamino group indicated that rotation may occur by thermal fluctuation during each phase. When the diethylamino group is rotated by 90° in the N* form, the oscillator strength becomes zero, which may be critical in nonradiative decay pathways. For the bending motion, we found a conical intersection, which could be a key pathway of nonradiative decay. By employing molecular orbital analysis, we concluded that the electronic structure changes induced by ESIPT play a key role in determining the decay pathways. Additionally, we compared the fluorescence quantum yield in acetonitrile with that in cyclohexane and showed that the solvent polarity also affects the radiative and nonradiative mechanisms of DEAHF.

Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Direct Methanol Fuel Cell (DMFC) are considered as future power sources in overcoming the fossil-based energy crisis. The objective of this work is to explore one of the natural resources of Indonesia and to improve its properties by chemical modification in order to get the required characteristics as electrolyte membrane. In this work coconut water was used as the basic material. It was fermented by Acetobacter xylinum and the resulting bacterial cellulose was then phosphorylated using a microwave-assisted reaction. Those membranes have been immersed for a varied time ranging between 0 and 8 hours (0-8 h) in a mixture of N,N-dimethylformamide (DMF), phosphoric acid and urea prior to irradiation by microwave for 60 s. Those membranes were characterized by several methods, such as functional group analysis by FTIR, proton conductivity, ion exchange capacity, swelling index, morphology analysis by SEM and phosphorus content analysis by SEM-EDS. From the experimental data, it can be concluded that a phosphorylated bacterial cellulose prepared by a 4h–immersion could be used as an alternative electrolyte membrane for fuel cell applications.Keywords: fuel cell, bacterial cellulose, phosphorylated bacterial cellulose  ABSTRAK Sel bahan bakar membran polimer eletrolit (PEMFC) dan sel bahan bakar metanol (DMFC) merupakan sumber energi masa depan yang dapat mengatasi krisis energi minyak bumi. Tujuan penelitian ini adalah untuk menggunakan bahan alam Indonesia yang dimodifikasi secara kimiawi supaya sifat-sifatnya dapat ditingkatkan untuk memenuhi persyaratan sebagai membran elektrolit. Dalam penelitian ini air kelapa telah digunakan sebagai bahan dasar dan selanjutnya difermentasi oleh Acetobacter xylinum. Selulosa bakterial yang dihasilkan difosforilasi dengan bantuan gelombang mikro. Membran tersebut direndam selama waktu yang bervariasi ( 0-8 jam) dalam campuran N,N-dimetilasetamida (DMF), asam fosfat dan urea sebelum diiradiasi dengan gelombang mikro selama 60 detik. Karakterisasi membran dilakukan dengan berbagai metoda, antara lain analisis gugus fungsi dengan FTIR, konduktivitas proton, kapasitas penukar ion, indeks penggembungan, analisis morfologi dengan SEM dan analisis kadar fosfor dengan SEM-EDS. Dari data yang diperoleh disimpulkan bahwa selulosa bakterial yang difosforilasi dengan proses perendaman selama 4 jam dapat digunakan sebagai alternatif untuk membran elektrolit dalam aplikasi sel bahan bakar.Kata kunci: sel bahan bakar, selulosa bakterial, selulosa bakterial terfosforilasi