Unimolecular Exciplexes by Ugi Four-Component Reaction.

Maria Ochs,Thomas J J Müller,Bernhard Mayer

doi:10.3389/fchem.2019.00717

Abstract

Exciplex or excited complex emission is an excited state process, arising from considerable charge transfer of an excited energy donor to an acceptor, which can be identified by the occurrence of a redshifted emission band that is absent in the individual constituents. Particularly interesting are exciplexes that are formed by intramolecular excited state interaction, which are inherently concentration independent. Based upon our previous experience in the Ugi-4CR syntheses of donor-acceptor conjugates capable of photo-induced intramolecular electron transfer (PIET), that is, generation of light-induced charge separation, we now disclose the diversity-oriented approach on unimolecular exciplex emitters and their reference systems by Ugi-4CR. The photophysics is studied by absorption and emission spectroscopy and accompanied by density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations.

Highlights

Exciplexes and excimers are emissive charge-transfer complexes, which are formed by excitation of one of the constituting chromophores that in turn collides with a second chromophore in its electronic ground state (Balzani et al, 2003; Balzani, 2008)
As part of our program to methodologically develop concise syntheses of functional chromophores by multicomponent reactions (MCR) (Levi and Müller, 2016a), we are interested in MCR syntheses of fluorophores (Levi and Müller, 2016b; Riva et al, 2016; Merkt and Müller, 2018; Müller, 2018) and donor-acceptor systems that interact in the excited state via photo-induced electron transfer (PIET) (Kavarnos, 1993; Lemmetyinen et al, 2011; Wenger, 2011; Ricks et al, 2012; Vauthey, 2012), as shown by non-radiative fluorescence quenching (Bucci and Müller, 2006; Bay et al, 2013, 2014; Bay and Müller, 2014)
Encouraged by Ugi 4CR syntheses of a phenothiazineanthraquinone-based photo-induced intramolecular electron transfer (PIET) system and related dyads (Bay et al, 2013, 2014; Bay and Müller, 2014), characterized by cyclic voltammetry, steady-state UV/vis, and fluorescence spectroscopy, as well as femtosecond transient absorption spectroscopy for identification of the desired charge separated state after light excitation, we decided to transpose the Ugi 4CR to a novel synthesis of N,N-dimethylaniline-anthracene dyads, which are known to form exciplex emitters (Hui and Ware, 1976)

Summary

INTRODUCTION

Molecular luminescence (Lakowicz, 2006; Valeur and Berberan-Santos, 2012) is a widespread phenomenon of functional organic materials (Müller and Bunz, 2007) and finds broad application in many fields of science and technology, ranging from fundamental science (luminescence spectroscopy) (Wolfbeis, 1993; Valeur and Brochon, 2012) over biophysical analytics (Chen et al, 1998; Nilsson et al, 2002; Wagenknecht, 2008; Demchenko et al, 2009; Kim and Park, 2009; Cairo et al, 2010), diagnostics (Kobayashi et al, 2010; Carter et al, 2014), and dye lasers (Thiel, 2000; Shankarling and Jarag, 2010) to sensors (Loving et al, 2010; Klymchenko, 2017; Zhang et al, 2017) and organic light-emitting diodes (OLED) (Müllen and Scherf, 2006; Park et al, 2011; Thejo Kalayani and Dhoble, 2012; Li, 2015). As part of our program to methodologically develop concise syntheses of functional chromophores by multicomponent reactions (MCR) (Levi and Müller, 2016a), we are interested in MCR syntheses of fluorophores (Levi and Müller, 2016b; Riva et al, 2016; Merkt and Müller, 2018; Müller, 2018) and donor-acceptor systems that interact in the excited state via photo-induced electron transfer (PIET) (Kavarnos, 1993; Lemmetyinen et al, 2011; Wenger, 2011; Ricks et al, 2012; Vauthey, 2012), as shown by non-radiative fluorescence quenching (Bucci and Müller, 2006; Bay et al, 2013, 2014; Bay and Müller, 2014). The absorption and emission spectroscopic characteristics are reported and discussed in the light of DFT and TDDFT calculations of the donoracceptor systems

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT