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Structure, Dynamics, and Disorder in Excited States of Photoresponsive Conjugated Materials

Event Details

Event Dates: 

Friday, January 29, 2016 - 4:00pm

Seminar Location: 

  • JILA Auditorium

Speaker Name(s): 

Art Braggs

Speaker Affiliation(s): 

John Hopkins University
Seminar Type/Subject

Scientific Seminar Type: 

  • Phys Chem/Chem Phys Seminar

Event Details & Abstract: 

Conjugation is a key attribute of many organic materials (e.g. photovoltaics and photoswitches) and there is continued interest in tailoring conjugated moieties and their interactions in order to control their photoresponses.  A critical step in this direction is to understand relationships between structure at the intra- and intermolecular levels and photoinduced behaviors (dynamics).  In this talk we present our efforts to illuminate structural properties and dynamics of excited states in conjugated materials as well as structure-dynamics relationships that underlie their photoresponsive behaviors.  Experimentally we utilize femtosecond stimulated Raman spectroscopy in combination with time-resolved electronic spectroscopies to interrogate variations in local structure and delocalization and to probe nuclear dynamics induced by excitation. We present work with poly- and oligothiophenes demonstrating that ultrafast evolution in excited-state conformation and exciton localization can be tracked through time-dependence in Raman frequencies and in mode-specific resonance enhancements (bottom left).  We further illustrate that resonance enhancement enables photoselectivity for interrogating the nature of various structural motifs that support localized excited and charge-separated states in aggregated materials (center).  Finally we describe multiplicity-specific, isomer-dependent switching mechanisms in thiophene-based photoswitches (right); the role of multiexcitonic states in switch activation and implications for photoswitch design are discussed.