A triple-stranded ladder coordination polymer, [Pb-3(bpe)(3)(O2C-CF3)(4)(O2CCH3)(2)] [bpe = trans-1,2-bis(4-pyridyl)ethene] undergoes a photochemical [2 + 2] cycloaddition reaction in the solid state to furnish 100% rctt-tetrakis(4-pyridyl)cyclobutane (rctt-tpcb) in two steps via cooperative molecular movements of the partially dimerized products formed initially.