Development of Novel Ferrocene-Containing BODIPY Dyes for

Light Harvesting ApplicationsPaloma Prieto, Burhan Hussein, Jennifer Huynh, Malek El-Aooiti, Bryan D. Koivisto*

Department of Chemistry and Biology. Ryerson University, 350 Victoria Street, Toronto ON, Canada, M5B 2K3

4th Annual Ryerson Science Symposium Wednesday August 19th, 2015

Facing the global energy demand

The high energy requirements of the 21st century have made it necessary to explore

renewable energy sources as a replacement for fossil fuels. In an effort to reduce

environmental pollution and address climate change, solar energy has become

increasingly significant.

To scale with the map, this is the surface area

needed to be covered by solar panels (at 20%

efficiency) to supply the increased global

energy demand projected for 2030 (22.7 TW):1

Shown is a proposed allocation of this area

according to energy use distribution.

Solar power vastly exceeds global energy requirements .

Dye-sensitized solar cells (DSSCs) Chromophore design

Ferrocene is a good electron

donor and provides redox stability

without competing against

BODIPY for photon absorption

Acetylene bridge

relieves steric

strain, allowing for

successful synthesis

BODIPY encourages

light absorption and

charge transfer

Cyanoacetic acid accepts the

excited electron density and

anchors the dye to TiO2

Tunable phenyl

group increases

solubility

Additional acceptors studied:

Aldehyde Malonitrile

DONOR π-SPACER ACCEPTOR

Synthetic pathway

A considerable number of D-π-A dyes containing

ferrocene and BODIPY (4,4-difluoro-4-bora-3a,4a-

diaza-s-indacene) can be prepared.

This project focuses on the synthesis and

characterization of dyes involving the following 4 R-

group substituents:

Reference electron-

donating

electron-

withdrawing

Apart from mildly tuning the orbital energies of the

dyes, the phenyl rings lie orthogonal to the BODIPY

core and interrupt π- stacking interactions which

otherwise cause serious solubility issues.

This next-generation photovoltaic

technology is cheaper than traditional

silicon solar cells and has efficiencies

upwards of 10%. The transparency of the

devices also makes them useful for

windows and other applications.2

In the device, light absorbed by the dye

excites an electron into a higher energy

state (1) and allows it to be injected into the

conduction band of TiO2 (2). It travels to

the conducting glass anode (3), along the

circuit, and back to a platinum cathode. An

electrolyte then regenerates the original

dye (4, 5).

An electron push-pull molecule is ideal for DSSC applications:

Light absorption profiles

The extended π-conjugation of the dyes and the use of the BODIPY core, which is

well known as an intense absorber, result in panchromatic dyes.

Electrochemistry

Cyclic voltammetry shows a reversible oxidation process ensuring that the dye can

be regenerated once it has given up an electron.

Frontier molecular orbitals

Conclusions and future work

References1Surface Area Required to Fuel the World With Solar.

http://landartgenerator.org/blagi/archives/127 (Accessed Aug 7th, 2015).

2Basic Research Needs for Solar Energy Utilization, U.S. Department of Energy Office of

Basic Energy Sciences, Apr 21, 2005.

0.0E+00

2.0E+04

4.0E+04

350 450 550 650 750

Mo

lar

Ab

sorp

tivit

y, ε

(M

-1cm

-1)

Wavelength, λ (nm)

UV-Vis spectra of ferrocene-BODIPY-aldehyde family

-25

-5

15

35

55

0.25 1 1.75Cu

rren

t (μ

A)

Applied Voltage (V vs. NHE)

Characteristic cyclic voltammogram of ferrocene-containing

BODIPY dyes

first oxidation

½ wave potential

(0.90 V)

HOMO -1

HOMO

LUMO

LUMO + 1

This project describes the successful ongoing synthesis and characterization of a new

ferrocene-BODIPY dye family. These molecules exhibit broad light absorption profiles,

distinct electron density shifts between the ground and excited states, and good redox

reversibility. DSSC device testing and optimization is needed to verify the dye

performance.

Density Functional Theory (DFT)

calculations show a desirable shift

of electronic density from the

donor, through the π-spacer, to

the acceptor region upon

excitation.

The dominant electronic transition

evidenced in the light absorption

profile is HOMO-1 to LUMO.

Charge separation in the excited

state encourages electron

injection into the TiO2 conduction

band. This reduces the probability

of electron relaxation back to the

ground state.

1a 30%

b 30%

c 48%

d 30%

2a 73%

b 42%

c 74%

d 66%

3a 35%

b 43%

c 48%

d 77%

4c 51%

5b 28%

c 33%

a b c d